Proceedings

Editorial

Jump to: Other

4 pages, 5085 KiB

Open AccessEditorial

Quantum Information Science in Italy (IQIS 2018 Editorial)

by G. Falci, E. Paladino, G. M. Palma, G. G. N. Angilella, A. La Magna and F. M. D. Pellegrino

Proceedings 2019, 12(1), 1; https://doi.org/10.3390/proceedings2019012001 - 21 Jun 2019

Viewed by 2112

Abstract

The 11th Italian Quantum Information Science conference (IQIS 2018) took place in Catania, Italy, at the Monastero dei Benedettini, from September 17 to 20, 2018. IQIS 2018 was organized by the Department of Physics and Astronomy “E. Majorana” of the University of Catania, [...] Read more.

The 11th Italian Quantum Information Science conference (IQIS 2018) took place in Catania, Italy, at the Monastero dei Benedettini, from September 17 to 20, 2018. IQIS 2018 was organized by the Department of Physics and Astronomy “E. Majorana” of the University of Catania, and by IMM-CNR, Catania. The conference also hosted an event dedicated to the FET-Flagship 2018/28 on Quantum Technologies. These proceedings collect papers contributed by the participants, which extend presentations delivered at the conference, and were subjected to peer-reviewing. They provide a snapshot of the contributions (mainly, but only) by the Italian scientific community to the developing field of quantum information and related subjects. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Other

Jump to: Editorial

4 pages, 270 KiB

Open AccessProceeding Paper

Preserving Nonclassicality in Noisy Communication Channels

by Alessia Allevi and Maria Bondani

Proceedings 2019, 12(1), 3; https://doi.org/10.3390/proceedings2019012003 - 25 Jun 2019

Cited by 1 | Viewed by 1204

Abstract

Nowadays, the transmission of quantum information, especially for the distribution of cryptographic keys, is required on a global scale. The main obstacle to overcome in free-space communication is the presence of turbulence, which causes both spatial and temporal deformations of the light signals [...] Read more.

Nowadays, the transmission of quantum information, especially for the distribution of cryptographic keys, is required on a global scale. The main obstacle to overcome in free-space communication is the presence of turbulence, which causes both spatial and temporal deformations of the light signals that code information. Here we investigate the extent at which the transmission of mesoscopic twin-beam states through asymmetric noisy channels degrades the nonclassical nature of the photon-number correlations between signal and idler. We consider three nonclassicality criteria, all written in terms of measurable quantities, and demonstrate, both theoretically and experimentally, that the asymmetry introduced by losses affects the three criteria in different ways. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 403 KiB

Open AccessProceeding Paper

Hilbert Space Structure Induced by Quantum Probes

by Go Kato, Masaki Owari and Koji Maruyama

Proceedings 2019, 12(1), 4; https://doi.org/10.3390/proceedings2019012004 - 25 Jun 2019

Viewed by 1217

Abstract

It is unrealistic to control all of the degrees of freedom of a high-dimensional quantum system. Here, we consider a scenario where our direct access is restricted to a small subsystem S that is constantly interacting with the rest of the system E [...] Read more.

It is unrealistic to control all of the degrees of freedom of a high-dimensional quantum system. Here, we consider a scenario where our direct access is restricted to a small subsystem S that is constantly interacting with the rest of the system E. What we investigate is the fundamental structures of the Hilbert space and the algebra of hamiltonians that are caused solely by the restrictedness of the direct control. One key finding is that hamiltonians form a Jordan algebra, and this leads to a significant observation that there is a sharp distinction between the cases of dimH_S ≥ 3 and dimH_S = 2 in terms of the nature of possible operations in E. Since our analysis is totally free from specific properties of any physical systems, it would form a solid basis for obtaining deeper insights into quantum control related issues, such as controllability and observability. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 216 KiB

Open AccessProceeding Paper

Entropy Area Law in Quantum Field Theories and Spin Systems

by Salvatore Mancani

Proceedings 2019, 12(1), 5; https://doi.org/10.3390/proceedings2019012005 - 3 Jun 2019

Viewed by 1560

Abstract

The entanglement entropy measures quantum correlations and it can be seen as the uncertainty on a quantum state. In one spatial dimension, the entanglement entropy scales as the boundary that divides two subsystems, so an area law has been proposed. However, the entanglement [...] Read more.

The entanglement entropy measures quantum correlations and it can be seen as the uncertainty on a quantum state. In one spatial dimension, the entanglement entropy scales as the boundary that divides two subsystems, so an area law has been proposed. However, the entanglement entropy diverges logarithmically at conformally invariant critical points, so the area law does not hold. The purpose of the work is to find a way to get more information about a critical state. The ground state of the Heisenberg XXZ model at criticality is analyzed by means of critical Ising eigenstates. Two ways of analysis are followed: a basis made of Ising eigenstates is built up and used to represent the XXZ ground state, then the Shannon entropy in the new basis is computed; the adiabatic evolution from the Ising ground state to the XXZ ground state. The result is that the Shannon entropy in the Ising basis scales linearly with the length of the system, while a phase transition is encountered during the adiabatic evolution. The conclusion is that there is no net gain in information after the procedure and possibly it is related to the fact the two systems stand in different phases. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 490 KiB

Open AccessProceeding Paper

Coexistence of Different Scaling Laws for the Entanglement Entropy in a Periodically Driven System

by Tony J. G. Apollaro and Salvatore Lorenzo

Proceedings 2019, 12(1), 6; https://doi.org/10.3390/proceedings2019012006 - 25 Jun 2019

Viewed by 1143

Abstract

The out-of-equilibrium dynamics of many body systems has recently received a burst of interest, also due to experimental implementations. The dynamics of observables, such as magnetization and susceptibilities, and quantum information related quantities, such as concurrence and entanglement entropy, have been investigated under [...] Read more.

The out-of-equilibrium dynamics of many body systems has recently received a burst of interest, also due to experimental implementations. The dynamics of observables, such as magnetization and susceptibilities, and quantum information related quantities, such as concurrence and entanglement entropy, have been investigated under different protocols bringing the system out of equilibrium. In this paper we focus on the entanglement entropy dynamics under a sinusoidal drive of the tranverse magnetic field in the 1D quantum Ising model. We find that the area and the volume law of the entanglement entropy coexist under periodic drive for an initial non-critical ground state. Furthermore, starting from a critical ground state, the entanglement entropy exhibits finite size scaling even under such a periodic drive. This critical-like behaviour of the out-of-equilibrium driven state can persist for arbitrarily long time, provided that the entanglement entropy is evaluated on increasingly subsytem sizes, whereas for smaller sizes a volume law holds. Finally, we give an interpretation of the simultaneous occurrence of critical and non-critical behaviour in terms of the propagation of Floquet quasi-particles. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 287 KiB

Open AccessProceeding Paper

Continuous Variable Entanglement in Non-Zero Orbital Angular Momentum States

by Adriana Pecoraro, Filippo Cardano, Lorenzo Marrucci and Alberto Porzio

Proceedings 2019, 12(1), 7; https://doi.org/10.3390/proceedings2019012007 - 11 Oct 2019

Cited by 1 | Viewed by 1207

Abstract

Orbital angular momentum is a discrete degree of freedom that can access an infinite dimensional Hilbert space, thus enhancing the information capacity of a single optical beam. Continuous variables field quadratures allow achieving some quantum tasks in a more advantageous way with respect [...] Read more.

Orbital angular momentum is a discrete degree of freedom that can access an infinite dimensional Hilbert space, thus enhancing the information capacity of a single optical beam. Continuous variables field quadratures allow achieving some quantum tasks in a more advantageous way with respect to the use of photon-number states. Here, we use a hybrid approach realizing bipartite continuous-variable Gaussian entangled state made up of two electromagnetic modes carrying orbital angular momentum. A q-plate is used for endowing a pair of entangled beams with such a degree of freedom. This quantum state is then completely characterized thanks to a novel design of a homodyne detector in which also the local oscillator is an orbital angular momentum-carrying beams so allowing the direct detection of vortex modes quadratures. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 1823 KiB

Open AccessProceeding Paper

Manipulating Quantum Many-Body Systems in the Presence of Controllable Dissipation

by Davide Rossini

Proceedings 2019, 12(1), 8; https://doi.org/10.3390/proceedings2019012008 - 25 Jun 2019

Viewed by 1225

Abstract

We discuss two quantum simulation schemes in which the coupling to an external bath may give rise to novel and interesting many-body physics. Namely, we first address the effect of local Markovian baths on the quantum annealing dynamics of an Ising-like chain: deviations [...] Read more.

We discuss two quantum simulation schemes in which the coupling to an external bath may give rise to novel and interesting many-body physics. Namely, we first address the effect of local Markovian baths on the quantum annealing dynamics of an Ising-like chain: deviations from adiabaticity may display a nonmonotonic trend as a function of the annealing time, as a result of the competition between nonadiabatic effects and dissipative processes. Secondly, we provide a framework to induce persistent currents through the coupling with a structured reservoir which generates nonreciprocity, without the need of any applied gauge field. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
(a) Setup for QA protocols. The various sites interact through time-varying Hamiltonian terms <math display="inline"> <semantics> <mrow> <msub> <mi>H</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>j</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mrow> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math>, and are locally coupled to independent reservoirs. (b,c) Excess energy as a function of the annealing time <math display="inline"> <semantics> <mi>τ</mi> </semantics> </math>, for a quantum Ising chain locally coupled to: (b) a bath inducing incoherent decay mechanisms; (c) an Ohmic bath of quantum harmonic oscillators at different temperature T. Full article ">Figure 2
(a) Setup to create persistent currents. The cavities interact unitarily via local Hamiltonian terms <math display="inline"> <semantics> <msub> <mi>H</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>j</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> </semantics> </math> and dissipatively via engineered reservoirs induced by the dissipators <math display="inline"> <semantics> <mrow> <mi mathvariant="script">D</mi> <mo>[</mo> <msub> <mi>L</mi> <mrow> <mi>j</mi> <mo>,</mo> <mi>j</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>]</mo> </mrow> </semantics> </math>. (b,c) Circulating current <math display="inline"> <semantics> <msubsup> <mrow> <mi mathvariant="script">I</mi> </mrow> <mi>j</mi> <mi>η</mi> </msubsup> </semantics> </math> for a minimal scheme of non-local dissipation, as a function of: (b) the parameters <math display="inline"> <semantics> <mrow> <mi>α</mi> <mo>,</mo> <mi>δ</mi> </mrow> </semantics> </math> (cluster mean-field data); (c) the system size L (exact diagonalization up to <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>=</mo> <mn>8</mn> </mrow> </semantics> </math>. Consistent results have been obtained with matrix product operators, enabling to reach much longer sizes [<a href="#B17-proceedings-12-00008" class="html-bibr">17</a>]). Full article ">

5 pages, 957 KiB

Open AccessProceeding Paper

Experimental Investigation of Quantum Decay via Integrated Photonics

by Andrea Crespi, Francesco V. Pepe, Paolo Facchi, Fabio Sciarrino, Paolo Mataloni, Hiromichi Nakazato, Saveri Pascazio and Roberto Osellame

Proceedings 2019, 12(1), 9; https://doi.org/10.3390/proceedings2019012009 - 11 Jun 2019

Cited by 1 | Viewed by 1384

Abstract

Whereas classical physics generally predicts an exponential trend for the temporal decay of an unstable state, quantum mechanics provides a rather different description. The decay is initially quadratic, while at very large times it follows a power-law. Actually, the latter regime has never [...] Read more.

Whereas classical physics generally predicts an exponential trend for the temporal decay of an unstable state, quantum mechanics provides a rather different description. The decay is initially quadratic, while at very large times it follows a power-law. Actually, the latter regime has never been observed experimentally. Here we employ arrays of femtosecond-laser-written optical waveguides to optically realize quantum systems where a discrete state is coupled to and can decay into a continuum. The transverse optical modes represent distinct quantum states of the photon and the temporal evolution of the system is mapped into the longitudinal propagation coordinate. By injecting laser light in the fabricated structures, and by imaging with high dynamic range the scattered light from above, we are able to observe experimentally different decay regimes, including the power-law tail. This process can be viewed as the quantum simulation of a quantum decay phenomenon. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
(a) Typical temporal evolution of the survival probability <math display="inline"> <semantics> <mrow> <mi>p</mi> <mo>(</mo> <mi>t</mi> <mo>)</mo> </mrow> </semantics> </math> of a discrete quantum state coupled to a continuum, where different regimes can be observed at short, intermediate and late evolution times. (b) The system is a linear array of optical waveguides, coupled by evanescent-field interaction, excited with coherent light. The first waveguide represents the discrete state and is coupled to the remaining part of the array, which acts as a continuum of states. The temporal evolution of the system is mapped into the longitudinal propagation coordinate t. See the text for details. Full article ">Figure 2
Coherent light from a He:Ne laser is injected in the array. To characterize the light distribution in the photonic structure, scattered light is imaged from above using a movable microscope-assembly that scans automatically the full length of the glass chip (a). Panel (b) reports an example of acquired intensity distribution from a waveguide array. The original image is monochrome and corresponds to a physical region of about 88 mm × 640 <math display="inline"> <semantics> <mi mathvariant="sans-serif">μ</mi> </semantics> </math>m; here it is reshaped for better readability and shown in false colors. A horizontal section yields the time evolution of a given state (waveguide). A vertical section gives the probability distribution within the photonic modes at a given time. Laser light is coupled in the array from the left in the topmost waveguide; the intensity of the first line in the picture thus corresponds to the survival probability of the initial state. Full article ">Figure 3
(a) Experimental survival probability in a weakly coupled system (<math display="inline"> <semantics> <mrow> <msub> <mi>κ</mi> <mn>0</mn> </msub> <mo><</mo> <mi>κ</mi> </mrow> </semantics> </math>). The measured points (black dots) are encircled by a gray area indicating the experimental uncertainty. (b) Experimental survival probability in a system with stronger coupling (<math display="inline"> <semantics> <mrow> <msub> <mi>κ</mi> <mn>0</mn> </msub> <mo>∼</mo> <mi>κ</mi> </mrow> </semantics> </math>); the red dashed line is a fitted <math display="inline"> <semantics> <mrow> <mi>C</mi> <msup> <mi>t</mi> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </msup> </mrow> </semantics> </math> asymptotic trend. Full article ">

4 pages, 233 KiB

Open AccessProceeding Paper

Two-Qubits in a Large-S Environment

by Eliana Fiorelli, Alessandro Cuccoli and Paola Verrucchi

Proceedings 2019, 12(1), 10; https://doi.org/10.3390/proceedings2019012010 - 13 Jun 2019

Cited by 1 | Viewed by 1527

Abstract

We analytically express the loss of entanglement between the components of a quantum device due to the generation of quantum correlations with its environment, and show that such loss diminishes when the latter is macroscopic and displays a semi-classical behaviour. We model the [...] Read more.

We analytically express the loss of entanglement between the components of a quantum device due to the generation of quantum correlations with its environment, and show that such loss diminishes when the latter is macroscopic and displays a semi-classical behaviour. We model the problem as a device made of a couple of qubits with a magnetic environment: this choice allows us to implement the above condition of semi-classical macroscopicity in terms of a large-S condition, according to the well known equivalence between classical and

S \to \infty

limit. A possible strategy for protecting internal entanglement exploiting the mechanism of domain-formation typical of critical dynamics is also suggested. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
<math display="inline"> <semantics> <msub> <mi>C</mi> <mrow> <msub> <mi>Q</mi> <mn>1</mn> </msub> <msub> <mi>Q</mi> <mn>2</mn> </msub> </mrow> </msub> </semantics> </math> as a function of S. In the inset <math display="inline"> <semantics> <mrow> <mrow> <mo>|</mo> </mrow> <msubsup> <mi>C</mi> <mrow> <msub> <mi>Q</mi> <mn>1</mn> </msub> <msub> <mi>Q</mi> <mn>2</mn> </msub> </mrow> <mn>2</mn> </msubsup> <mo>−</mo> <msub> <mi>τ</mi> <msub> <mi>Q</mi> <mn>1</mn> </msub> </msub> <mrow> <mo>|</mo> </mrow> </mrow> </semantics> </math> as a function of S. Each line correspond to a specific choice of <math display="inline"> <semantics> <msub> <mi>x</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </semantics> </math> and <math display="inline"> <semantics> <msub> <mi>y</mi> <mrow> <mi>m</mi> <mi>a</mi> <mi>x</mi> </mrow> </msub> </semantics> </math> (see text). Full article ">

6 pages, 735 KiB

Open AccessProceeding Paper

Advances in Sequential Measurement and Control of Open Quantum Systems

by Stefano Gherardini, Andrea Smirne, Matthias M. Müller and Filippo Caruso

Proceedings 2019, 12(1), 11; https://doi.org/10.3390/proceedings2019012011 - 24 Jun 2019

Cited by 5 | Viewed by 1370

Abstract

Novel concepts, perspectives and challenges in measuring and controlling an open quantum system via sequential schemes are shown. We discuss how similar protocols, relying both on repeated quantum measurements and dynamical decoupling control pulses, can allow to: (i) Confine and protect quantum dynamics [...] Read more.

Novel concepts, perspectives and challenges in measuring and controlling an open quantum system via sequential schemes are shown. We discuss how similar protocols, relying both on repeated quantum measurements and dynamical decoupling control pulses, can allow to: (i) Confine and protect quantum dynamics from decoherence in accordance with the Zeno physics. (ii) Analytically predict the probability that a quantum system is transferred into a target quantum state by means of stochastic sequential measurements. (iii) Optimally reconstruct the spectral density of environmental noise sources by orthogonalizing in the frequency domain the filter functions driving the designed quantum-sensor. The achievement of these tasks will enhance our capability to observe and manipulate open quantum systems, thus bringing advances to quantum science and technologies. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

5 pages, 280 KiB

Open AccessProceeding Paper

Dynamical Casimir Effect and State Transfer in the Ultrastrong Coupling Regime

by Giuliano Benenti, Michele Stramacchia and Giuliano Strini

Proceedings 2019, 12(1), 12; https://doi.org/10.3390/proceedings2019012012 - 20 Jun 2019

Cited by 1 | Viewed by 1452

Abstract

The dynamical Casimir effect (DCE) manifests itself in the ultrastrong matter-field coupling (USC) regime, as a consequence of the nonadiabatic change of some parameters of a system. We show that the DCE is a fundamental limitation for standard quantum protocols based on quantum [...] Read more.

The dynamical Casimir effect (DCE) manifests itself in the ultrastrong matter-field coupling (USC) regime, as a consequence of the nonadiabatic change of some parameters of a system. We show that the DCE is a fundamental limitation for standard quantum protocols based on quantum Rabi oscillations, implying that new schemes are required to implement high-fidelity ultrafast quantum gates. Our results are illustrated by means of a paradigmatic quantum communication protocol, i.e., quantum state transfer. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
(Left) for the initial state <math display="inline"> <semantics> <mrow> <mrow> <mo>|</mo> <mi>ψ</mi> <mo>〉</mo> </mrow> <mo>=</mo> <msqrt> <mrow> <mn>0.2</mn></mrow> </msqrt> <mrow> <mo>|</mo> <mi>g</mi> <mo>〉</mo> </mrow> <mo>+</mo> <mi>i</mi> <msqrt> <mrow> <mn>0.8</mn></mrow> </msqrt> <mrow> <mo>|</mo> <mi>e</mi> <mo>〉</mo> </mrow> </mrow> </semantics> </math>, fidelity F (full curve, left axis) and mean photon number <math display="inline"> <semantics> <mrow> <mo>〈</mo> <mi>n</mi> <mo>〉</mo> </mrow> </semantics> </math> (right axis, dashed curve) as a function of the qubit-cavity coupling strength g. The mean photon number is also shown for the pure DCE (dot-dashed curve). (Right) Contour plot for fidelity F as a function of the Bloch sphere angles <math display="inline"> <semantics> <mi>θ</mi> </semantics> </math> and <math display="inline"> <semantics> <mi>φ</mi> </semantics> </math> for the input state, at <math display="inline"> <semantics> <mrow> <mi>g</mi> <mo>=</mo> <mn>0.4</mn></mrow> </semantics> </math>. Full article ">

5 pages, 250 KiB

Open AccessProceeding Paper

Privacy in Quantum Estimation

by Milajiguli Rexiti and Stefano Mancini

Proceedings 2019, 12(1), 13; https://doi.org/10.3390/proceedings2019012013 - 25 Jun 2019

Viewed by 1243

Abstract

We introduce the notion of privacy in quantum estimation by considering an one-parameter family of isometries taking one input into two output systems. It stems on the separate and adversarial control of the two output systems as well as on the local minimization [...] Read more.

We introduce the notion of privacy in quantum estimation by considering an one-parameter family of isometries taking one input into two output systems. It stems on the separate and adversarial control of the two output systems as well as on the local minimization of the mean square error. Applications to two-qubit unitaries (with one qubit in a fixed input state) are presented. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 255 KiB

Open AccessProceeding Paper

Quantum Enhanced Optical Measurements: From Ultra-High Sensitivity in Absorption Measurements to Ghost Microscopy

by Elena Losero, Ivano Ruo-Berchera, Alessio Avella, Alice Meda and Marco Genovese

Proceedings 2019, 12(1), 14; https://doi.org/10.3390/proceedings2019012014 - 25 Jul 2019

Viewed by 1356

Abstract

Quantum enhanced optical measurement protocols aim at reducing the uncertainty in the estimation of some physical quantities of a system below the shot-noise limit, classically unavoidable. In particular when small number of photons is used the shot noise can be the main source [...] Read more.

Quantum enhanced optical measurement protocols aim at reducing the uncertainty in the estimation of some physical quantities of a system below the shot-noise limit, classically unavoidable. In particular when small number of photons is used the shot noise can be the main source of uncertainty, in these cases the use of quantum light is of great interest. Note that there are several situations where the number of photons in the probe can not be increased arbitrarily, as when fragile biological samples are under investigation. Two different imaging protocols are discussed in the following. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 296 KiB

Open AccessProceeding Paper

Continuous and Pulsed Quantum Control

by Giovanni Gramegna, Daniel Burgarth, Paolo Facchi and Saverio Pascazio

Proceedings 2019, 12(1), 15; https://doi.org/10.3390/proceedings2019012015 - 24 Jun 2019

Cited by 1 | Viewed by 1388

Abstract

We consider two alternative procedures which can be used to control the evolution of a generic finite-dimensional quantum system, one hinging upon a strong continuous coupling with a control potential and the other based on the application of frequently repeated pulses onto the [...] Read more.

We consider two alternative procedures which can be used to control the evolution of a generic finite-dimensional quantum system, one hinging upon a strong continuous coupling with a control potential and the other based on the application of frequently repeated pulses onto the system. Despite the practical and conceptual difference between them, they lead to the same dynamics, characterised by a partitioning of the Hilbert space into sectors among which transitions are inhibited by dynamical superselection rules. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 268 KiB

Open AccessProceeding Paper

Ferromagnetic Josephson Junctions for High Performance Computation

by Roberta Caruso, Davide Massarotti, Alessandro Miano, Vitaly V. Bolginov, Aymen Ben Hamida, Liubov N. Karelina, Igor V. Vernik, Valery V. Ryazanov, Oleg A. Mukhanov, Giovanni Piero Pepe and Francesco Tafuri

Proceedings 2019, 12(1), 16; https://doi.org/10.3390/proceedings2019012016 - 25 Jun 2019

Viewed by 1637

Abstract

Josephson junctions drive the operation of superconducting qubits and they are the key for the coupling and the interfacing of superconducting qubit components with other quantum platforms. They are the only means to introduce non linearity in a superconducting circuit and offer direct [...] Read more.

Josephson junctions drive the operation of superconducting qubits and they are the key for the coupling and the interfacing of superconducting qubit components with other quantum platforms. They are the only means to introduce non linearity in a superconducting circuit and offer direct solutions to tune the properties of a superconducting qubit, thus enlarging the possible qubit layouts. Junctions performances and tunability can take advantage of using a large variety of barriers and their special functionalities. We mention pertinent results on the advances in understanding the properties of ferromagnetic junctions, which makepossible the use of these devices either as memory elements and as core circuit elements. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
(a) <math display="inline"> <semantics> <mrow> <msub> <mi>I</mi> <mi>C</mi> </msub> <mrow> <mo>(</mo> <mi>H</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> at 3.5 K. Black squares correspond to an external magnetic field ramped from positive to negative values, red circles are obtained ramping the field from negative to positive values. Lines are plotted as a guide for the eye. Green dotted line represents the chosen working point. Inset: magnetization curve for the same sample, obtained using the technique described in [<a href="#B8-proceedings-12-00016" class="html-bibr">8</a>]. Red and black arrows indicate the positive and negative coercive field <math display="inline"> <semantics> <msub> <mi>H</mi> <mi>C</mi> </msub> </semantics> </math> on the two curves. Blue arrow indicates the saturation field <math display="inline"> <semantics> <msub> <mi>H</mi> <mi>S</mi> </msub> </semantics> </math> on both curves. (b,c) <math display="inline"> <semantics> <mrow> <mi>I</mi> <mo>(</mo> <mi>V</mi> <mo>)</mo> </mrow> </semantics> </math> curves corresponding to the points highlighted by green dotted line in panel (a), which are the two critical current levels used as logical states. The insets show the combination of magnetic field pulses and RF trains used to induce the switch between the two states. Full article ">Figure 2
(a) Critical current levels obtained using RF trains with different nominal energies. (b) Sketch of the MJJ in parallel with the shunting capacitance <math display="inline"> <semantics> <msub> <mi>C</mi> <mi>B</mi> </msub> </semantics> </math> typical of the transmon design. Full article ">

4 pages, 279 KiB

Open AccessProceeding Paper

The Friedrichs-Lee Model and Its Singular Coupling Limit

by Davide Lonigro, Paolo Facchi and Marilena Ligabò

Proceedings 2019, 12(1), 17; https://doi.org/10.3390/proceedings2019012017 - 24 Jun 2019

Cited by 3 | Viewed by 1581

Abstract

Lee’s field-theoretical model describes the interaction between a qubit and a structured bosonic field. We study the mathematical properties of the Hamiltonian of the single-excitation sector of the theory, including a possibly “singular” qubit-field coupling (i.e., mediated by a non-square integrable form factor). [...] Read more.

Lee’s field-theoretical model describes the interaction between a qubit and a structured bosonic field. We study the mathematical properties of the Hamiltonian of the single-excitation sector of the theory, including a possibly “singular” qubit-field coupling (i.e., mediated by a non-square integrable form factor). This result allows for a rigorous description of qubit-field interactions in many physically interesting systems and may be extended to higher-excitation sectors of the theory. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 190 KiB

Open AccessProceeding Paper

Exciting Dressed BICs Via Photon Scattering and Delayed Quantum Feedback

by Giuseppe Calajó, Yao-Lung L. Fang, Harold U. Baranger and Francesco Ciccarello

Proceedings 2019, 12(1), 18; https://doi.org/10.3390/proceedings2019012018 - 2 Jul 2019

Viewed by 1596

Abstract

We consider a semi-infinite waveguide with linear dispersion coupled to a qubit, in which a dressed bound state in the continuum (BIC) is known to exist. We predict that this BIC can be excited with significant probability via multi-photon scattering in the non-Markovian [...] Read more.

We consider a semi-infinite waveguide with linear dispersion coupled to a qubit, in which a dressed bound state in the continuum (BIC) is known to exist. We predict that this BIC can be excited with significant probability via multi-photon scattering in the non-Markovian regime where the photon delay time (corresponding to the qubit-mirror distance) is of the order of the qubit’s decay time. A similar process excites the BIC existing in an infinite waveguide coupled to a pair of qubits, yielding stationary entanglement between them. This shows, in particular, that photon trapping via scattering can occur without band-edge effects or cavities, the essential resource being instead the delayed quantum feedback due to the mirror. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

5 pages, 202 KiB

Open AccessProceeding Paper

Slow Dynamics and Thermodynamics of Open Quantum Systems

by Vasco Cavina, Andrea Mari and Vittorio Giovannetti

Proceedings 2019, 12(1), 19; https://doi.org/10.3390/proceedings2019012019 - 10 Jul 2019

Cited by 1 | Viewed by 1225

Abstract

We develop a perturbation theory to estimate the finite time corrections around a quasi static trajectory, in which a quantum system is able to equilibrate at each instant with its environment. The results are then applied to non equilibrium thermodynamics, in which context [...] Read more.

We develop a perturbation theory to estimate the finite time corrections around a quasi static trajectory, in which a quantum system is able to equilibrate at each instant with its environment. The results are then applied to non equilibrium thermodynamics, in which context we are able to provide a connection between the irreversible contributions and the microscopic details of the dynamical map generating the evolution. Turning the attention to finite time Carnot engines, we found a universal connection between the spectral density esponent of the hot/cold thermal baths and the efficiency at maximum power, giving also a new interpretation to already known results such as the Curzon-Ahborn and the Schmiedl-Seifert efficiencies. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

5 pages, 258 KiB

Open AccessProceeding Paper

Grassmannization of the 3D Ising Model

by E. Martello, G. G. N. Angilella and L. Pollet

Proceedings 2019, 12(1), 20; https://doi.org/10.3390/proceedings2019012020 - 6 Jun 2019

Viewed by 1360

Abstract

The application of Feynman’s diagrammatic technique to classical link models with local constraints seems impossible due to (i) the absence of a free Gaussian theory on top of which the perturbative expansion can be constructed, and (ii) Dyson’s collapse argument, rendering the perturbative [...] Read more.

The application of Feynman’s diagrammatic technique to classical link models with local constraints seems impossible due to (i) the absence of a free Gaussian theory on top of which the perturbative expansion can be constructed, and (ii) Dyson’s collapse argument, rendering the perturbative expansion divergent. However, we show for the classical 3D Ising model how both problems can be circumvented using a Grassmann representation. This makes it possible to obtain an expansion of the spin correlation function and the magnetic susceptibility in terms of the inverse temperature in the thermodynamic limit, through which the values for the critical temperature and critical index g are evaluated within 1.6% and 5.4% of their accepted values, respectively. Our work is a straightforward adaptation of the theory previously developed in an earlier paper. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

3 pages, 193 KiB

Open AccessProceeding Paper

Supervised Quantum State Discrimination

by Marco Fanizza, Andrea Mari and Vittorio Giovannetti

Proceedings 2019, 12(1), 21; https://doi.org/10.3390/proceedings2019012021 - 19 Jul 2019

Cited by 1 | Viewed by 1081

Abstract

Combining machine learning and quantum information. [...] Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

4 pages, 262 KiB

Open AccessProceeding Paper

Extraction of Work via a Thermalization Protocol

by Nicolò Piccione, Benedetto Militello, Anna Napoli and Bruno Bellomo

Proceedings 2019, 12(1), 22; https://doi.org/10.3390/proceedings2019012022 - 4 Jul 2019

Cited by 1 | Viewed by 1516

Abstract

This extended abstract contains an outline of the work reported at the conference IQIS2018. We show that it is possible to exploit a thermalization process to extract work from a resource system R to a bipartite system S. To do this, we [...] Read more.

This extended abstract contains an outline of the work reported at the conference IQIS2018. We show that it is possible to exploit a thermalization process to extract work from a resource system R to a bipartite system S. To do this, we propose a simple protocol in a general setting in the presence of a single bath at temperature T and then examine it when S is described by the quantum Rabi model at

T = 0

. We find the theoretical bounds of the protocol in the general case and we show that when applied to the Rabi model it gives rise to a satisfactory extraction of work and efficiency. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 1025 KiB

Open AccessProceeding Paper

Effects of Indistinguishability in a System of Three Identical Qubits

by Alessia Castellini, Rosario Lo Franco and Giuseppe Compagno

Proceedings 2019, 12(1), 23; https://doi.org/10.3390/proceedings2019012023 - 22 Jul 2019

Cited by 1 | Viewed by 1450

Abstract

Quantum correlations of identical particles are important for quantum-enhanced technologies. The recently introduced non-standard approach to treat identical particles is here exploited to show the effect of particle indistinguishability on the characterization of entanglement of three identical qubits. We show that, by spatially [...] Read more.

Quantum correlations of identical particles are important for quantum-enhanced technologies. The recently introduced non-standard approach to treat identical particles is here exploited to show the effect of particle indistinguishability on the characterization of entanglement of three identical qubits. We show that, by spatially localized measurements in separated regions, three independently-prepared separated qubits in a pure elementary state behave as distinguishable ones, as expected. On the other hand, delocalized measurements make it emerge a measurement-induced entanglement. We then find that three independently-prepared boson qubits under complete spatial overlap exhibit genuine three-partite entanglement. These results evidence the effect of spatial overlap on identical particle entanglement and show that the latter depends on both the quantum state and the type of measurement. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

6 pages, 451 KiB

Open AccessProceeding Paper

Digital Quantum Simulations of Spin Models on Hybrid Platform and Near-Term Quantum Processors

by Francesco Tacchino, Alessandro Chiesa, Matthew D. LaHaye, Ivano Tavernelli, Stefano Carretta and Dario Gerace

Proceedings 2019, 12(1), 24; https://doi.org/10.3390/proceedings2019012024 - 9 Jul 2019

Viewed by 1230

Abstract

Digital quantum simulators are among the most appealing applications. [...] Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
Digital quantum simulation of the tunnelling of the total magnetization in a spin-1 Hamiltonian. (a) Numerical results for the proposed electromechanical set-up, for different values of the NRs <math display="inline"> <semantics> <msub> <mi>T</mi> <mn>2</mn> </msub> </semantics> </math> time. (b) Experimental data from the IBM Q ibmqx2-Yorktown real backend, for different choices of the pair of qubits selected on the chip. Full article ">Figure 2
Digital quantum simulation of the TIM. (a) Numerical results obtained for the proposed electromechanical set-up, for different values of the NRs <math display="inline"> <semantics> <msub> <mi>T</mi> <mn>2</mn> </msub> </semantics> </math> and <math display="inline"> <semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>10</mn> </mrow> </semantics> </math> Suzuki-Trotter iterations, compared to the corresponding ideal results (for the same digital decomposition in <math display="inline"> <semantics> <mrow> <mi>n</mi> <mo>=</mo> <mn>10</mn> </mrow> </semantics> </math> steps). (b–d) Experimental data from the IBM Q ibmqx5-Rueschlikon real backend, for increasing values of the number of Suzuki-Trotter iterations. The dashed line represents the exact result with no digital error. Full article ">

5 pages, 1542 KiB

Open AccessProceeding Paper

Dissipative Synthesis of Mechanical Fock-Like States

by Matteo Brunelli and Oussama Houhou

Proceedings 2019, 12(1), 25; https://doi.org/10.3390/proceedings2019012025 - 19 Jul 2019

Viewed by 1355

Abstract

The observation of genuine quantum features of nano-mechanical motion is a key goal for both fundamental and applied quantum science. To this end, a promising approach is the stabilization of nonclassical features in the presence of dissipation, by means of the tunable coupling [...] Read more.

The observation of genuine quantum features of nano-mechanical motion is a key goal for both fundamental and applied quantum science. To this end, a promising approach is the stabilization of nonclassical features in the presence of dissipation, by means of the tunable coupling with a photonic environment. Here we present a scheme that combines dissipative squeezing with a mechanical nonlinearity to stabilize arbitrary approximations of (displaced) mechanical Fock state of any number. We consider an optomechanical system driven by three control lasers---at the cavity resonance and at the two mechanical sidebands---that couple the amplitude of the cavity field to the resonator's position and position squared. When the amplitude of the resonant drive is tuned to some specific values, the mechanical steady state is found in a (displaced) superposition of a finite number of Fock states, which for large enough squeezing achieves near-unit fidelity with a (displaced) Fock state of any desired number. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
Wigner function <math display="inline"> <semantics> <mrow> <mi>W</mi> <mrow> <mo>(</mo> <mi>q</mi> <mo>,</mo> <mi>p</mi> <mo>)</mo> </mrow> <mo>=</mo> <mfrac> <mn>1</mn> <mi>π</mi> </mfrac> <msub> <mo>∫</mo> <mi mathvariant="double-struck">R</mi> </msub> <mi mathvariant="normal">d</mi> <mi>y</mi> <mspace width="0.166667em"/> <msup> <mi>e</mi> <mrow> <mn>2</mn> <mi>i</mi> <mi>p</mi> <mi>y</mi> </mrow> </msup> <msub> <mi>φ</mi> <mn>5</mn> </msub> <msup> <mrow> <mo>(</mo> <mi>q</mi> <mo>+</mo> <mi>y</mi> <mo>)</mo> </mrow> <mo>*</mo> </msup> <msub> <mi>φ</mi> <mn>5</mn> </msub> <mrow> <mo>(</mo> <mi>q</mi> <mo>−</mo> <mi>y</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> of the state <math display="inline"> <semantics> <mrow> <mrow> <mo>|</mo> </mrow> <msub> <mi>φ</mi> <mn>5</mn> </msub> <mrow> <mo>〉</mo> </mrow> </mrow> </semantics> </math> for different values <math display="inline"> <semantics> <mrow> <mi>ζ</mi> <mo>=</mo> <mn>0.99</mn></mrow> </semantics> </math> (left), <math display="inline"> <semantics> <mrow> <mi>ζ</mi> <mo>=</mo> <mn>0.9</mn></mrow> </semantics> </math> (centre), <math display="inline"> <semantics> <mrow> <mi>ζ</mi> <mo>=</mo> <mn>0.7</mn></mrow> </semantics> </math> (right). Full article ">

4 pages, 497 KiB

Open AccessProceeding Paper

May a Dissipative Environment Be Beneficial for Quantum Annealing?

by Gianluca Passarelli, Giulio De Filippis, Vittorio Cataudella and Procolo Lucignano

Proceedings 2019, 12(1), 26; https://doi.org/10.3390/proceedings2019012026 - 9 Jul 2019

Viewed by 1223

Abstract

We discuss the quantum annealing of the fully-connected ferromagnetic p-spin model in a dissipative environment at low temperature. This model, in the large p limit, encodes in its ground state the solution to the Grover’s problem of searching in unsorted databases. In [...] Read more.

We discuss the quantum annealing of the fully-connected ferromagnetic p-spin model in a dissipative environment at low temperature. This model, in the large p limit, encodes in its ground state the solution to the Grover’s problem of searching in unsorted databases. In the framework of the quantum circuit model, a quantum algorithm is known for this task, providing a quadratic speed-up with respect to its best classical counterpart. This improvement is not recovered in adiabatic quantum computation for an isolated quantum processor. We analyze the same problem in the presence of a low-temperature reservoir, using a Markovian quantum master equation in Lindblad form, and we show that a thermal enhancement is achieved in the presence of a zero temperature environment moderately coupled to the quantum annealer. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

7 pages, 538 KiB

Open AccessProceeding Paper

Experimental Connection between the Instrumental and Bell Inequalities

by Iris Agresti, Gonzalo Carvacho, Davide Poderini, Leandro Aolita, Rafael Chaves and Fabio Sciarrino

Proceedings 2019, 12(1), 27; https://doi.org/10.3390/proceedings2019012027 - 18 Jul 2019

Cited by 5 | Viewed by 1578

Abstract

An investigated process can be studied in terms of the causal relations among the involved variables, representing it as a causal model. Some causal models are particularly relevant, since they can be tested through mathematical constraints between the joint probability distributions of the [...] Read more.

An investigated process can be studied in terms of the causal relations among the involved variables, representing it as a causal model. Some causal models are particularly relevant, since they can be tested through mathematical constraints between the joint probability distributions of the observables. This is a valuable tool because, if some data violates the constraints of a causal model, the implication is that the observed statistics is not compatible with that causal structure. Strikingly, when non-classical correlations come to play, a discrepancy between classical and quantum causal predictions can arise, producing a quantum violation of the classical causal constraints. The simplest
scenario admitting such quantum violation is given by the instrumental causal processes. Here, we experimentally violate an instrumental test on a photonic platform and show how the quantum correlations violating the CHSH inequality can be mapped into correlations violating an instrumental test, despite the different forms of non-locality they display. Indeed, starting from a Bell-like scenario, we recover the violation of the instrumental scenario through a map between the two behaviours, which includes a post-selection of data and then we test an alternative way to violate the CHSH inequality, adopting the instrumental process platform. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
Directed Acyclic Graphs representing causal models. In this figure, we show three different causal models represented by Directed Acyclic Graphs (DAG) [<a href="#B2-proceedings-12-00027" class="html-bibr">2</a>], where each node represents a variable and the arrows link variables between whom there is a causal relationship. (a) This is the simplest causal model in which a variable A has an influence over B, but it has no testable mathematical constraints characterizing the allowed joint probabilities <math display="inline"> <semantics> <mrow> <mi>p</mi> <mo>(</mo> <mi>a</mi> <mo>,</mo> <mi>b</mi> <mo>)</mo> </mrow> </semantics> </math>. (b) The causal model of a CHSH scenario, where the parties Alice (A) and Bob (B) share a system and choose the basis on which to measure it according two independent variables, X and Y. Hence, no communication must occur between A and B. (c) DAG representing the instrumental scenario, whose main difference from the CHSH Bell-like scenario, is the presence of a classical channel of communication between the parties, i.e., A has a causal influence over B. Full article ">Figure 2
Experimental Apparatus. We generate a singlet state through a SPDC process (constituting our hidden variable <math display="inline"> <semantics> <mo>Λ</mo> </semantics> </math>) that is shared by the two parties A and B. On A’s path, the measurement station is made by a HWP followed by a PBS, since the qubits are encoded in the polarization of the photons. On B’s path, there is an analogous measurement station, but, before the HWP <math display="inline"> <semantics> <msub> <mi>H</mi> <mn>2</mn> </msub> </semantics> </math>, we put a Pockels cell, to switch from one operator to the other, in the case of active feed-forward, i.e., triggering a high voltage application to the Pockels cell and making it behave as a HWP, while, when it is not triggered, it performs the identity. The voltage application is triggered by Alice’s detector <math display="inline"> <semantics> <msub> <mi>A</mi> <mn>1</mn> </msub> </semantics> </math> (i.e., corresponding to output 0), whose signal is split and sent both to a coincidence counter and to the Pockels cell. In the post-selection case, the Pockels cell is not triggered and A and B choose independently the measurement basis, performing the desired observables rotating respectively <math display="inline"> <semantics> <msub> <mi>H</mi> <mn>1</mn> </msub> </semantics> </math> and <math display="inline"> <semantics> <msub> <mi>H</mi> <mn>2</mn> </msub> </semantics> </math>. Full article ">Figure 3
Experimental results. In this plot we show the experimental quantum violations of Bonet and CHSH inequalities obtained from 16 experimental runs in the post-selection regime (for both scenarios the classical upper bound is 2). In purple and blue, we show respectively the Bonet’s and CHSH violations obtained through the apparatus described in <a href="#proceedings-12-00027-f002" class="html-fig">Figure 2</a> section, keeping the Pockels cell switched off and performing Alice’s and Bob’s measurements, rotating the HWPs. In orange, we show the extent of the Bonet inequality’s violation that can be obtained from the probabilities p(a,b|x,y) belonging to the CHSH scenario. In green, we show the CHSH violation obtained on an instrumental process platform, through an alternative procedure which does not require the correlations between all of the 4 combinations of the inputs (x,y). Full article ">

5 pages, 1003 KiB

Open AccessProceeding Paper

Machine Learning for Quantum Metrology

by Nicolò Spagnolo, Alessandro Lumino, Emanuele Polino, Adil S. Rab, Nathan Wiebe and Fabio Sciarrino

Proceedings 2019, 12(1), 28; https://doi.org/10.3390/proceedings2019012028 - 23 Aug 2019

Cited by 1 | Viewed by 2148

Abstract

Phase estimation represents a significant example to test the application of quantum theory for enhanced measurements of unknown physical parameters. Several recipes have been developed, allowing to define strategies to reach the ultimate bounds in the asymptotic limit of a large number of [...] Read more.

Phase estimation represents a significant example to test the application of quantum theory for enhanced measurements of unknown physical parameters. Several recipes have been developed, allowing to define strategies to reach the ultimate bounds in the asymptotic limit of a large number of trials. However, in certain applications it is crucial to reach such bound when only a small number of probes is employed. Here, we discuss an asymptotically optimal, machine learning based, adaptive single-photon phase estimation protocol that allows us to reach the standard quantum limit when a very limited number of photons is employed. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

8 pages, 293 KiB

Open AccessProceeding Paper

Quantum Sensing 1/f Noise via Pulsed Control of a Two-Qubit Gate

by Antonio D’Arrigo, Giuseppe Falci and Elisabetta Paladino

Proceedings 2019, 12(1), 29; https://doi.org/10.3390/proceedings2019012029 - 25 Jul 2019

Cited by 1 | Viewed by 1156

Abstract

Dynamical decoupling sequences are a convenient tool to reduce decoherence due to intrinsic fluctuations with

1 / f

power spectrum hindering quantum circuits. We study the possibility to achieve an efficient universal two-qubit gate in the presence of

1 / f

noise by [...] Read more.

Dynamical decoupling sequences are a convenient tool to reduce decoherence due to intrinsic fluctuations with

1 / f

power spectrum hindering quantum circuits. We study the possibility to achieve an efficient universal two-qubit gate in the presence of

1 / f

noise by periodic and Carr-Purcell dynamical decoupling. The high degree of selectivity achieved by these protocols also provides a valuable tool to infer noise characteristics, as the high-frequency cut off and the noise variance. Different scalings of the gate error with noise variance signal the contribution of different noise statistical properties to the gate error. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

6 pages, 228 KiB

Open AccessProceeding Paper

Kick and Fix: The Roots of Quantum Control

by Paolo Facchi and Saverio Pascazio

Proceedings 2019, 12(1), 30; https://doi.org/10.3390/proceedings2019012030 - 19 Jul 2019

Cited by 3 | Viewed by 1252

Abstract

When two operators A and B do not commute, the calculation of the exponential operator

e^{A + B}

is a difficult and crucial problem. The applications are vast and diversified: to name but a few examples, quantum evolutions, product formulas, quantum control, [...] Read more.

When two operators A and B do not commute, the calculation of the exponential operator

e^{A + B}

is a difficult and crucial problem. The applications are vast and diversified: to name but a few examples, quantum evolutions, product formulas, quantum control, Zeno effect. The latter are of great interest in quantum applications and quantum technologies. We present here a historical survey of results and techniques, and discuss differences and similarities. We also highlight the link with the strong coupling regime, via the adiabatic theorem, and contend that the “pulsed” and “continuous” formulations differ only in the order by which two limits are taken, and are but two faces of the same coin. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

3 pages, 294 KiB

Open AccessProceeding Paper

Reciprocal Quantum Channels

by Vittorio Giovannetti and Matteo Rosati

Proceedings 2019, 12(1), 31; https://doi.org/10.3390/proceedings2019012031 - 19 Jul 2019

Viewed by 1160

Abstract

We report the presence of an asymmetry that arises when considering the performances of quantum communication channels whose outputs are connected via a rigid, distance-preserving, yet not completely-positive, transformation. From a classical perspective these transmission lines should exhibit the same communication efficiency which [...] Read more.

We report the presence of an asymmetry that arises when considering the performances of quantum communication channels whose outputs are connected via a rigid, distance-preserving, yet not completely-positive, transformation. From a classical perspective these transmission lines should exhibit the same communication efficiency which is lost in the quantum setting. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

6 pages, 2538 KiB

Open AccessProceeding Paper

Tailoring Active Defect Centers During the Growth of Group IV Crystals

by Michele Cascio, Ioannis Deretzis, Giuseppe Fisicaro, Giuseppe Falci, Giovanni Mannino and Antonino La Magna

Proceedings 2019, 12(1), 32; https://doi.org/10.3390/proceedings2019012032 - 19 Dec 2019

Viewed by 1033

Abstract

Defects, e.g., Vacancies (Vs) and Defect-impurity centers, e.g., Nitrogen-Vacancy complexes (NVs), in group IV materials (diamond, SiC, graphene) are unique systems for Quantum Technologies (QT). The control of their positioning is a key issue for any realistic QT application and their tailored inclusion [...] Read more.

Defects, e.g., Vacancies (Vs) and Defect-impurity centers, e.g., Nitrogen-Vacancy complexes (NVs), in group IV materials (diamond, SiC, graphene) are unique systems for Quantum Technologies (QT). The control of their positioning is a key issue for any realistic QT application and their tailored inclusion during controlled crystal-growth processes could overcome the limitations of other incorporation methods (e.g., ion implantation causing strong lattice damage). To date, the atomistic evolution regarding the growth of group IV crystals is barely known and this missing knowledge often results in a lack of process control in terms of mesoscopic crystal quality, mainly concerning the eventual generation of local or extended defects and their space distribution. We have developed Kinetic Monte Carlo models to study the growth kinetics of materials characterized by sp

^{3}

bonding symmetries with an atomic-level accuracy. The models can be also coupled to the continuum simulation of the gas-phase status generated in the equipment to estimate the deposition rate and reproduce a variety of growth techniques (e.g., Chemical and Physical Vapour deposition, sublimation, etc.). Evolution is characterized by nucleation and growth of ideal or defective structures and their balance depends critically on process-related parameters. Quantitative predictions of the process evolution can be obtained and readily compared with the structural characterization of the processed samples. In particular, we can describe the surface state of the crystal and the defect generation/evolution (for both point and extended defects, e.g., stacking faults) as a function of the initial substrate conditions and the process parameters (e.g., temperature, pressure, gas flow). Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
Schematic of the local bonding rearrangement due to deposition/evaporation events in the case of coordination = 1 value (Coor = 1) [panel (a)] and Coor = 2 [panel (b)]. Large gray and light brown spheres indicate Ad-Atoms (e.g., C and Si) while small white spheres indicate Ad-Voids. For a deposition event in the case of coordination = 1 value (Coor = 1) the local bonding configuration (Armchair or Zigzag) has to be statistically selected. The bonding network is undetermined for an AdVoid with Coor = 1 while it is fixed for both an Ad-Void and Ad-Atom with Coor = 2 and Coor = 3, see e.g., panel (b) where a Zigzag type of bonding is shown. Full article ">Figure 2
(a) Transmission electron microscopy of a silicon nanocrystal grown by the plasma assisted process. The diffraction analysis in the inset evidences the diamond configuration. (b) Snapshot of the simulated growth process of a silicon nano-crystal starting from a cubic seed. Only under coordinated surface atoms and vacancies (red spots) are shown. Full article ">Figure 3
Top panel: snapshot of the simulated growth process of a silicon carbide nanocrystal starting from a cubic seed. In the left figure only under coordinated surface atoms and vacancies (red spots) are shown. In the center figure, the atoms which are not in epitaxial order with the seed. In the right figure, the vacancy distribution in the bulk region of the nanocrystal. Bottom panel in the left figure examples of configurations (analyzed by transmission electron microscopy) of a silicon carbide nanocrystal grown by a plasma assisted process are shown. In the right figure, high resolution analysis of one nanocrystal reveals stacking fault-type defects. Full article ">

6 pages, 373 KiB

Open AccessProceeding Paper

Graphene Josephson Junction Quantum Circuits for Noise Detection

by Francesco Maria Dimitri Pellegrino, Giuseppe Falci and Elisabetta Paladino

Proceedings 2019, 12(1), 33; https://doi.org/10.3390/proceedings2019012033 - 24 Jul 2019

Cited by 4 | Viewed by 1638

Abstract

Graphene Josephson Junctions (GJJ) in the regime of ballistic transport where current is carried by discrete energy states of Andreev-reflected coherent electron-hole pairs have been recently demonstrated in graphene heterostructures. Due to the non-linear current-phase relation, GJJ can be used as a sensitive [...] Read more.

Graphene Josephson Junctions (GJJ) in the regime of ballistic transport where current is carried by discrete energy states of Andreev-reflected coherent electron-hole pairs have been recently demonstrated in graphene heterostructures. Due to the non-linear current-phase relation, GJJ can be used as a sensitive probe of underlying microscopic noise sources. Here, we find an analytic expression for the supercurrent-phase relation in the finite low doping regime, and we sketch how a GJJ quantum circuit can play the role of noise quantum sensor. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
Panel (a): <math display="inline"> <semantics> <mrow> <mi mathvariant="script">J</mi> <mo>(</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </semantics> </math> defined in Equation (<a href="#FD7-proceedings-12-00033" class="html-disp-formula">7</a>) (solid black line) and <math display="inline"> <semantics> <mrow> <msub> <mi mathvariant="script">J</mi> <msub> <mi>a</mi> <mn>0</mn> </msub> </msub> <mrow> <mo>(</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> <mo>=</mo> <msub> <mi>a</mi> <mn>0</mn> </msub> <msub> <mi>I</mi> <mn>0</mn> </msub> <mrow> <mo>(</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> with <math display="inline"> <semantics> <mrow> <msub> <mi>a</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>0.112</mn></mrow> </semantics> </math> (dashed red line) in units of <math display="inline"> <semantics> <mrow> <mi>e</mi> <msub> <mi mathvariant="sans-serif">Δ</mi> <mn>0</mn> </msub> <mi>W</mi> <mo>/</mo> <mrow> <mo>(</mo> <mo>ℏ</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math> as a function of the phase <math display="inline"> <semantics> <mi>ϕ</mi> </semantics> </math>. Panel (b): Critical current, in units of <math display="inline"> <semantics> <mrow> <mi>e</mi> <msub> <mi mathvariant="sans-serif">Δ</mi> <mn>0</mn> </msub> <mi>W</mi> <mo>/</mo> <mrow> <mo>(</mo> <mo>ℏ</mo> <mi>L</mi> <mo>)</mo> </mrow> </mrow> </semantics> </math>, at low doping as a function of the Fermi level at zero temperature. The solid black line refers to the critical current obtained by maximing expression in Equation (<a href="#FD6-proceedings-12-00033" class="html-disp-formula">6</a>), the dashed red line is the approximation of the critical current given by Equation (<a href="#FD9-proceedings-12-00033" class="html-disp-formula">9</a>). Full article ">

7 pages, 249 KiB

Open AccessProceeding Paper

Incompatibility in Multi-Parameter Quantum Metrology with Fermionic Gaussian States

by Angelo Carollo, Bernardo Spagnolo and Davide Valenti

Proceedings 2019, 12(1), 34; https://doi.org/10.3390/proceedings2019012034 - 31 Jul 2019

Viewed by 1589

Abstract

In this article we derive a closed form expression for the incompatibility condition in multi-parameter quantum metrology when the reference states are Fermionic Gaussian states. Together with the quantum Fisher information, the knowledge of the compatibility condition provides a way of designing optimal [...] Read more.

In this article we derive a closed form expression for the incompatibility condition in multi-parameter quantum metrology when the reference states are Fermionic Gaussian states. Together with the quantum Fisher information, the knowledge of the compatibility condition provides a way of designing optimal measurement strategies for multi-parameter quantum estimation. Applications range from quantum metrology with thermal states to non-equilibrium steady states with Fermionic and spin systems. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

5 pages, 813 KiB

Open AccessProceeding Paper

Speedup of Adiabatic Multiqubit State-Transfer by Ultrastrong Coupling of Matter and Radiation

by Michele Stramacchia, Alessandro Ridolfo, Giuliano Benenti, Elisabetta Paladino, Francesco Maria Dimitri Pellegrino, Daniele Maccarrone and Giuseppe Falci

Proceedings 2019, 12(1), 35; https://doi.org/10.3390/proceedings2019012035 - 23 Jul 2019

Cited by 2 | Viewed by 1376

Abstract

Ultrastrongly coupled quantum hardware may increase the speed of quantum state processing in distributed architectures, allowing to approach fault-tolerant threshold. We show that circuit QED architectures in the ultrastrong coupling regime, which has been recently demonstrated with superconductors, may show substantial speedup for [...] Read more.

Ultrastrongly coupled quantum hardware may increase the speed of quantum state processing in distributed architectures, allowing to approach fault-tolerant threshold. We show that circuit QED architectures in the ultrastrong coupling regime, which has been recently demonstrated with superconductors, may show substantial speedup for a class of adiabatic protocols resilient to the main source of errors, namely the interplay of dynamical Casimir effect and cavity losses. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 1792 KiB

Open AccessProceeding Paper

Entanglement Assisted Transport of Two Walkers in Noisy Quantum Networks

by Maja Colautti and Filippo Caruso

Proceedings 2019, 12(1), 36; https://doi.org/10.3390/proceedings2019012036 - 25 Oct 2019

Viewed by 1084

Abstract

Understanding the transport mechanisms and properties of complex networks is fundamental for the comprehension of a vast class of phenomena, from state transfer on a spin network to light-harvesting in photosynthetic complexes. It has been theoretically and experimentally demonstrated that noise can enhance [...] Read more.

Understanding the transport mechanisms and properties of complex networks is fundamental for the comprehension of a vast class of phenomena, from state transfer on a spin network to light-harvesting in photosynthetic complexes. It has been theoretically and experimentally demonstrated that noise can enhance transport when the system parameters are properly tuned, an effect known as noise-assisted transport (NAT). In this work we investigate the role of initial entanglement in the transfer efficiency of two walkers in a noisy network. By using the formalism of quantum walks, we define a range of small dephasing noise where initial site-entanglement provides transport enhancement and outperforms the NAT effect. Furthermore, we show two specific scenarios where entanglement-assisted transport can open faster channels for slow walkers and avoid a broken link in a communication line. These findings may be of potential interest for quantum technologies. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
Transport to sink and entanglement evolution for the two initial configurations <math display="inline"> <semantics> <mrow> <mo>(</mo> <mi>j</mi> <mo>,</mo> <mi>k</mi> <mo>,</mo> <mi>m</mi> <mo>,</mo> <mi>n</mi> <mo>)</mo> <mo>=</mo> <mo>(</mo> <mn>1</mn> <mo>,</mo> <mn>6</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mn>7</mn> <mo>)</mo> </mrow> </semantics> </math> (top row of figures) and <math display="inline"> <semantics> <mrow> <mo>(</mo> <mi>j</mi> <mo>,</mo> <mi>k</mi> <mo>,</mo> <mi>m</mi> <mo>,</mo> <mi>n</mi> <mo>)</mo> <mo>=</mo> <mo>(</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mn>6</mn> <mo>,</mo> <mn>7</mn> <mo>)</mo> </mrow> </semantics> </math> (bottom row of figures) of a 7-site network. Colours refer to the different correlation between the excitation and control sites: green for <math display="inline"> <semantics> <mrow> <mi>E</mi> <mo>(</mo> <msub> <mi>t</mi> <mn>0</mn> </msub> <mo>)</mo> <mo>=</mo> <mn>1</mn> </mrow> </semantics> </math>, dark green for <math display="inline"> <semantics> <mrow> <mi>E</mi> <mo>(</mo> <msub> <mi>t</mi> <mn>0</mn> </msub> <mo>)</mo> <mo>=</mo> <mn>0.9</mn></mrow> </semantics> </math> and blue for two independent walkers. Solid lines are used for a pure coherent dynamics without dephasing, and dashed lines for the optimal NAT dynamics. (a,e) Transport efficiency to the sink as a function of time, with network scheme in the inset. (b,f) Transport efficiency at stationary conditions. (c,d,g,h) Time-evolution of entanglement. Full article ">Figure 2
Transport efficiency to the sink as a function of time for: (a,b) A dendrimer network where sites <math display="inline"> <semantics> <mrow> <mn>1</mn> <mo>,</mo> <mspace width="0.166667em"/> <mn>2</mn> </mrow> </semantics> </math> are directly connected to the sink while <math display="inline"> <semantics> <mrow> <mn>12</mn> <mo>,</mo> <mspace width="0.166667em"/> <mn>19</mn> </mrow> </semantics> </math> are separated from it by a double choice path. The investigated preparation states are <math display="inline"> <semantics> <mrow> <mo>(</mo> <mi>j</mi> <mo>,</mo> <mi>k</mi> <mo>,</mo> <mi>m</mi> <mo>,</mo> <mi>n</mi> <mo>)</mo> <mo>=</mo> <mo>(</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>,</mo> <mn>12</mn> <mo>,</mo> <mn>19</mn> <mo>)</mo> </mrow> </semantics> </math> and <math display="inline"> <semantics> <mrow> <mo>(</mo> <mi>j</mi> <mo>,</mo> <mi>k</mi> <mo>,</mo> <mi>m</mi> <mo>,</mo> <mi>n</mi> <mo>)</mo> <mo>=</mo> <mo>(</mo> <mn>12</mn> <mo>,</mo> <mn>19</mn> <mo>,</mo> <mn>1</mn> <mo>,</mo> <mn>2</mn> <mo>)</mo> </mrow> </semantics> </math>, as in the insets. (c,d) A continuum communication line with four input ports at the ends and the sink in the middle point. The preparation state holds as in the insets, with the excitation and the control sites at opposite ends. In (d), an internal channel between the excitation sites and the sink is damaged. Full article ">

6 pages, 4380 KiB

Open AccessProceeding Paper

Generation of Photon Pairs in the Light-Matter Ultrastrong Coupling Regime: From Casimir Radiation to Stimulated Raman Adiabatic Passage

by Alessandro Ridolfo

Proceedings 2019, 12(1), 37; https://doi.org/10.3390/proceedings2019012037 - 23 Jul 2019

Viewed by 1212

Abstract

The ultrastrong coupling regime of light-matter interaction is achieved when the coupling strength is a significant fraction of the natural frequencies of the noninteracting parts. Physics in this regime has recently attracted great interest, both theoretically and experimentally being a fruitful platform to [...] Read more.

The ultrastrong coupling regime of light-matter interaction is achieved when the coupling strength is a significant fraction of the natural frequencies of the noninteracting parts. Physics in this regime has recently attracted great interest, both theoretically and experimentally being a fruitful platform to test fundamental quantum mechanics in a new non-perturbative regime, and for applications to quantum technologies.Here we discuss the generation of photon-pair states, which is a distinctive feature of this new regime, and interesting new dynamicsl effects both in optomechanics and in circuit-QED architectures. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 220 KiB

Open AccessProceeding Paper

Efficiently Compressible Density Operators via Entropy Maximization

by Serena Di Giorgio and Paulo Mateus

Proceedings 2019, 12(1), 39; https://doi.org/10.3390/proceedings2019012039 - 2 Aug 2019

Cited by 1 | Viewed by 1329

Abstract

We address the problem of efficiently and effectively compress density operators (DOs), by providing an efficient procedure for learning the most likely DO, given a chosen set of partial information. We explore, in the context of quantum information theory, the generalisation of [...] Read more.

We address the problem of efficiently and effectively compress density operators (DOs), by providing an efficient procedure for learning the most likely DO, given a chosen set of partial information. We explore, in the context of quantum information theory, the generalisation of the maximum entropy estimator for DOs, when the direct dependencies between the subsystems are provided. As a preliminary analysis, we restrict the problem to tripartite systems when two marginals are known. When the marginals are compatible with the existence of a quantum Markov chain (QMC) we show that there exists a recovery procedure for the maximum entropy estimator, and moreover, that for these states many well-known classical results follow. Furthermore, we notice that, contrary to the classical case, two marginals, compatible with some tripartite state, might not be compatible with a QMC. Finally, we provide a new characterisation of quantum conditional independence in light of maximum entropy updating. At this level, all the Hilbert spaces are considered finite dimensional. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

5 pages, 584 KiB

Open AccessProceeding Paper

Degradation and Protection of Entanglement in Open Quantum Systems ^†

by Antonella De Pasquale

Proceedings 2019, 12(1), 40; https://doi.org/10.3390/proceedings2019012040 - 23 Jul 2019

Viewed by 1230

Abstract

The distribution of entangled quantum systems among the nodes of a network is a key task at the basis of the development of quantum technologies, e.g., quantum communication, quantum computation, etc. Many efforts have been devoted to identify strategies, based on pre- and [...] Read more.

The distribution of entangled quantum systems among the nodes of a network is a key task at the basis of the development of quantum technologies, e.g., quantum communication, quantum computation, etc. Many efforts have been devoted to identify strategies, based on pre- and post-processing operations or decoherence-free subspaces, to prevent the deterioration of such exotic correlations. However, all these approaches loose their usefulness when the noise level affecting the system surpasses a certain minimal threshold that leads to an entanglement-breaking dynamics. Here we attack this problem in the context of discrete- and continuous-time description of the system dynamics, providing some explicit examples in the context of qubit channels. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 1116 KiB

Open AccessProceeding Paper

Observing the Spectral Collapse of Two-Photon Interaction Models

by Simone Felicetti and Alexandre Le Boité

Proceedings 2019, 12(1), 41; https://doi.org/10.3390/proceedings2019012041 - 22 Jul 2019

Viewed by 1354

Abstract

Until very recently, two-photon interaction processes have been considered only as arising from second- or higher-order effects in driven systems, and so limited to extremely small coupling strengths. However, a variety of novel physical phenomena emerges in the strong and ultrastrong coupling regimes. [...] Read more.

Until very recently, two-photon interaction processes have been considered only as arising from second- or higher-order effects in driven systems, and so limited to extremely small coupling strengths. However, a variety of novel physical phenomena emerges in the strong and ultrastrong coupling regimes. Strikingly, for a critical value of the coupling strength the discrete spectrum collapses into a continuous band. In this extended abstract, we discuss recent proposals to implement genuine two-photon interactions in an undriven solid-state system, in the framework of circuit QED. In particular, we review counterintuitive spectral features of two-photon interaction models and we show how the onset of the spectral collapse can be observed in feasible scattering experiments. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
(a,b) Energy spectrum for the two-photon Dicke model (<a href="#FD1-proceedings-12-00041" class="html-disp-formula">1</a>) as a function of the coupling strength, for atoms resonant with the two-photon transition <math display="inline"> <semantics> <mrow> <msub> <mi>ω</mi> <mi>q</mi> </msub> <mo>=</mo> <mn>2</mn> <msub> <mi>ω</mi> <mi>c</mi> </msub> </mrow> </semantics> </math>. Panel (a) shows [<a href="#B20-proceedings-12-00041" class="html-bibr">20</a>] the spectrum for <math display="inline"> <semantics> <mrow> <mi>N</mi> <mo>=</mo> <mn>1</mn> </mrow> </semantics> </math>; different line styles denote the parity of the number of photons (positive for continuous red lines, negative for dotted black lines), which is a symmetry of <math display="inline"> <semantics> <msub> <mover accent="true"> <mi>H</mi> <mo>^</mo> </mover> <mrow> <mn>2</mn> <mi>p</mi> <mi>h</mi> </mrow> </msub> </semantics> </math>. Panel (b) shows [<a href="#B19-proceedings-12-00041" class="html-bibr">19</a>] the spectrum for <math display="inline"> <semantics> <mrow> <mi>N</mi> <mo>=</mo> <mn>3</mn> </mrow> </semantics> </math>, the solid red line corresponds to the two-photon Dicke <math display="inline"> <semantics> <msub> <mover accent="true"> <mi>H</mi> <mo>^</mo> </mover> <mrow> <mn>2</mn> <mi>p</mi> <mi>h</mi> </mrow> </msub> </semantics> </math>, while the yellow dashed line corresponds to the model obtained including inter-spin couplings <math display="inline"> <semantics> <mrow> <mi>J</mi> <msubsup> <mo>∑</mo> <mrow> <mi>i</mi> <mo>=</mo> <mn>1</mn> </mrow> <mrow> <mi>N</mi> <mo>−</mo> <mn>1</mn> </mrow> </msubsup> <msubsup> <mi>σ</mi> <mi>x</mi> <mi>i</mi> </msubsup> <msubsup> <mi>σ</mi> <mi>x</mi> <mrow> <mi>i</mi> <mo>+</mo> <mn>1</mn> </mrow> </msubsup> </mrow> </semantics> </math> of strength <math display="inline"> <semantics> <mrow> <mi>J</mi> <mo>=</mo> <mn>0.2</mn><msub> <mi>ω</mi> <mi>c</mi> </msub> </mrow> </semantics> </math>. (c,d) Fluorescence spectrum [<a href="#B20-proceedings-12-00041" class="html-bibr">20</a>] in arbitrary units of the output signal under coherent drive, for different values of the coupling strength. In (c) is shown the transition from the strong to the USC regime, while in (d) the fluorescence spectrum bears a direct signature of the onset of the spectral collapse. Full article ">

5 pages, 205 KiB

Open AccessProceeding Paper

Non-Equilibrium Phenomena in Quantum Systems, Criticality and Metastability

by Angelo Carollo, Bernardo Spagnolo and Davide Valenti

Proceedings 2019, 12(1), 43; https://doi.org/10.3390/proceedings2019012043 - 29 Sep 2019

Viewed by 1139

Abstract

We summarise here some relevant results related to non-equilibrium quantum systems. We characterise quantum phase transitions (QPT) in out-of-equilibrium quantum systems through a novel approach based on geometrical and topological properties of mixed quantum systems. We briefly describe results related to non-perturbative studies [...] Read more.

We summarise here some relevant results related to non-equilibrium quantum systems. We characterise quantum phase transitions (QPT) in out-of-equilibrium quantum systems through a novel approach based on geometrical and topological properties of mixed quantum systems. We briefly describe results related to non-perturbative studies of the bistable dynamics of a quantum particle coupled to an environment. Finally, we shortly summarise recent studies on the generation of solitons in current-biased long Josephson junctions. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

4 pages, 1288 KiB

Open AccessProceeding Paper

Manipulation of Cooper Pair Entanglement in Hybrid Topological Josephson Junctions

by Gianmichele Blasi, Fabio Taddei, Vittorio Giovannetti and Alessandro Braggio

Proceedings 2019, 12(1), 44; https://doi.org/10.3390/proceedings2019012044 - 16 Sep 2019

Viewed by 934

Abstract

The non-local manipulation of spin-entangled states by means of local gating in two parallel 2D topological insulators properly connected to two superconducting electrodes is studied. We calculate analytically the current-phase relationship of the Josephson current making use of the scattering matrix approach and [...] Read more.

The non-local manipulation of spin-entangled states by means of local gating in two parallel 2D topological insulators properly connected to two superconducting electrodes is studied. We calculate analytically the current-phase relationship of the Josephson current making use of the scattering matrix approach and we identify the various local and non-local scattering mechanisms. We show that the Josephson critical current, remarkably, allows a direct quantification of the entanglement manipulation. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Figure 1
Schematic representation of the setup: it consists of an heterostructure (say CdTe-HgTe) grown along the z-axis resulting in two layers of TIs. In gray are depicted the superconductors (<math display="inline"> <semantics> <msub> <mi>S</mi> <mrow> <mi>L</mi> <mo>/</mo> <mi>R</mi> </mrow> </msub> </semantics> </math>) while in green the TI planes. The arrowed blue (red) solid lines represent the 1D helical edge states with spin ↑ (↓). On the frontal side, in the x-z-plane of the scheme, are depicted two CAR processes where CP are non-locally splitted. The application of the Rashba and Zeeman-like fields due to the presence of side gates and the induced magnetic flux <math display="inline"> <semantics> <mo>Φ</mo> </semantics> </math>. Such a fields act in terms of the unitary operators <math display="inline"> <semantics> <mrow> <msubsup> <mi mathvariant="script">U</mi> <mi mathvariant="normal">B</mi> <mi mathvariant="normal">u</mi> </msubsup> <mrow> <mo>(</mo> <msub> <mi>θ</mi> <mi mathvariant="normal">B</mi> </msub> <mo>)</mo> </mrow> </mrow> </semantics> </math> and <math display="inline"> <semantics> <mrow> <msubsup> <mi mathvariant="script">U</mi> <mi>SO</mi> <mo>ℓ</mo> </msubsup> <mrow> <mo>(</mo> <msub> <mi>θ</mi> <mi>SO</mi> </msub> <mo>)</mo> </mrow> </mrow> </semantics> </math> (see text) on the upper and lower edges respectively. Full article ">

5 pages, 235 KiB

Open AccessProceeding Paper

Continuous Measurements for Advanced Quantum Metrology

by Francesco Albarelli, Matteo A. C. Rossi, Dario Tamascelli and Marco G. Genoni

Proceedings 2019, 12(1), 47; https://doi.org/10.3390/proceedings2019012047 - 4 Dec 2019

Viewed by 1589

Abstract

We review some recent results regarding the use of time-continuous measurements for quantum-enhanced metrology. First, we present the underlying quantum estimation framework and elucidate the correct figures of merit to employ. We then report results from two previous works where the system of [...] Read more.

We review some recent results regarding the use of time-continuous measurements for quantum-enhanced metrology. First, we present the underlying quantum estimation framework and elucidate the correct figures of merit to employ. We then report results from two previous works where the system of interest is an ensemble of two-level atoms (qubits) and the quantity to estimate is a magnetic field along a known direction (a frequency). In the first case, we show that, by continuously monitoring the collective spin observable transversal to the encoding Hamiltonian, we get Heisenberg scaling for the achievable precision (i.e.,

1 / N

for N atoms); this is obtained for an uncorrelated initial state. In the second case, we consider independent noises acting separately on each qubit and we show that the continuous monitoring of all the environmental modes responsible for the noise allows us to restore the Heisenberg scaling of the precision, given an initially entangled GHZ state. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

4 pages, 353 KiB

Open AccessProceeding Paper

Measuring Nonclassicality of Mesoscopic Twin-Beam States with Silicon Photomultipliers ^†

by Giovanni Chesi, Luca Malinverno, Alessia Allevi, Romualdo Santoro, Massimo Caccia and Maria Bondani

Proceedings 2019, 12(1), 48; https://doi.org/10.3390/proceedings2019012048 - 19 Nov 2019

Viewed by 1116

Abstract

The study of nonclassical properties of quantum states is a relevant topic for fundamental Quantum Optics and Quantum Information applications. In the mesoscopic domain, promising results have been obtained using photon-number-resolving detectors. Here we show recent results achieved with the class of Silicon [...] Read more.

The study of nonclassical properties of quantum states is a relevant topic for fundamental Quantum Optics and Quantum Information applications. In the mesoscopic domain, promising results have been obtained using photon-number-resolving detectors. Here we show recent results achieved with the class of Silicon Photomultipliers: by a proper analysis of the output signal, the nonclassicality of twin-beam states can be detected and exploited. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 196 KiB

Open AccessProceeding Paper

Two-Level Systems with Broken Inversion Symmetry

by Giovanni Scala

Proceedings 2019, 12(1), 49; https://doi.org/10.3390/proceedings2019012049 - 20 Nov 2019

Viewed by 1003

Abstract

This research analyzes the impact of the asymmetry of the quantum system and the range of control possibilities offered by dispersive media and the nanostructures. I investigated the asymmetric behavior of a two level system in the Jaynes-Cummings model (JC) and in the [...] Read more.

This research analyzes the impact of the asymmetry of the quantum system and the range of control possibilities offered by dispersive media and the nanostructures. I investigated the asymmetric behavior of a two level system in the Jaynes-Cummings model (JC) and in the spontaneous emission process discussing respectively the presence of a non trivial emission at the Rabi frequency and the correction at a much more basic level, i.e., in the lifetime of the excited state, and also affect the value of the Lamb shift with broken symmetry in the diagonal terms of dipole moment. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

4 pages, 514 KiB

Open AccessProceeding Paper

Dissipative Frustration in a One Dimensional Josephson Junction Chain

by Dominik Maile, Sabine Andergassen, Wolfgang Belzig and Gianluca Rastelli

Proceedings 2019, 12(1), 51; https://doi.org/10.3390/proceedings2019012051 - 19 Nov 2019

Viewed by 1238

Abstract

We study the influence of dissipative frustration on the one dimensional Josephson junction chain. In particular we analyze the dissipative quantum phase transition between the chain being superconducting or insulating, the purity as a measure of quantum—environment correlation and the logarithmic negativity as [...] Read more.

We study the influence of dissipative frustration on the one dimensional Josephson junction chain. In particular we analyze the dissipative quantum phase transition between the chain being superconducting or insulating, the purity as a measure of quantum—environment correlation and the logarithmic negativity as an entanglement measure. The dissipative frustration is provided by coupling two non-commuting operators to the environment. A possible realization of these environmental couplings are shunt resistances between the superconducting islands and resistances to the ground. Using a self-consistent harmonic approximation we determine the critical line separating superconducting and insulating phases and find a nonmonotonic behavior as a function of the dissipative strength. The interplay between both environmental couplings is also reflected in the purity and the logarithmic negativity. We find a change in their behavior depending whether a second bath is present or not. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 303 KiB

Open AccessProceeding Paper

Non-Ideal X-Gate and Z-Gate in Semiconducting Spin Qubit Implementations

by Elena Ferraro, Marco Fanciulli and Marco De Michielis

Proceedings 2019, 12(1), 53; https://doi.org/10.3390/proceedings2019012053 - 19 Nov 2019

Viewed by 1287

Abstract

Several spin qubit architectures have been proposed, theoretically investigated and realized at least on the scale of single devices in view of quantum computation and simulation applications. We focus our study on five qubit types: quantum dot spin qubit, double quantum dot singlet-triplet [...] Read more.

Several spin qubit architectures have been proposed, theoretically investigated and realized at least on the scale of single devices in view of quantum computation and simulation applications. We focus our study on five qubit types: quantum dot spin qubit, double quantum dot singlet-triplet qubit, double quantum dot hybrid qubit, donor qubit, quantum dot spin-donor qubit and for each one we derived a compact effective Hamiltonian. Single qubit gate fidelities when time interval error is included are compared. A realistic set of values for the error parameters of amplitude controls linked to the z and x contribution appearing in the Hamiltonian models has been used. This study provides a ranking of the gate fidelities for the different qubit architectures highlighting which one is the most robust with respect to the considered control noises. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 1790 KiB

Open AccessProceeding Paper

Multimode Cavity Optomechanics

by Paolo Piergentili, Letizia Catalini, Mateusz Bawaj, Stefano Zippili, Nicola Malossi, Riccardo Natali, David Vitali and Giovanni Di Giuseppe

Proceedings 2019, 12(1), 54; https://doi.org/10.3390/proceedings2019012054 - 12 Nov 2019

Cited by 2 | Viewed by 1276

Abstract

We study theoretically and experimentally the behavior of an optomechanical system where two vibrating dielectric membranes are placed inside a driven Fabry-Pérot cavity. We prove that multi–element systems of mechanical resonators are suitable for enhancing optomechanical performances, and we report a ∼2.47 gain [...] Read more.

We study theoretically and experimentally the behavior of an optomechanical system where two vibrating dielectric membranes are placed inside a driven Fabry-Pérot cavity. We prove that multi–element systems of mechanical resonators are suitable for enhancing optomechanical performances, and we report a ∼2.47 gain in the optomechanical coupling strength of the membrane relative motion with respect to the single membrane case. With this configuration it is possible to enable cavity optomechanics in the strong single-photon coupling regime. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 668 KiB

Open AccessProceeding Paper

Multiparameter Approach to Dynamic Quantum Phase Estimation

by Valeria Cimini, Ludovica Ruggiero, Ilaria Gianani, Marco Sbroscia, Tecla Gasperi, Emanuele Roccia, Luca Mancino, Marco G. Genoni, Daniela Tofani, Fabio Bruni, Maria Antonietta Ricci and Marco Barbieri

Proceedings 2019, 12(1), 55; https://doi.org/10.3390/proceedings2019012055 - 4 Dec 2019

Viewed by 1081

Abstract

We have applied techniques of quantum phase estimation to the dynamical tracking of the optical activity of a solution of sucrose undergoing acid hydrolysis. We adopt a multiparameter approach that makes the estimation reliable and robust against setup instabilities. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 707 KiB

Open AccessProceeding Paper

Implementation of POVMs by Projective Measurements and Postselection:Optimal Strategies and Applications to Unambiguous State Discrimination

by Filip B. Maciejewski and Michał Oszmaniec

Proceedings 2019, 12(1), 56; https://doi.org/10.3390/proceedings2019012056 - 19 Nov 2019

Viewed by 1285

Abstract

We present new results concerning simulation of general quantum measurements (POVMs) by projective measurements (PMs) for the task of Unambiguous State Discrimination (USD). We formulate a problem of finding optimal strategy of simulation for given quantum measurement. The problem can be solved for [...] Read more.

We present new results concerning simulation of general quantum measurements (POVMs) by projective measurements (PMs) for the task of Unambiguous State Discrimination (USD). We formulate a problem of finding optimal strategy of simulation for given quantum measurement. The problem can be solved for qubit and qutrits measurements by Semi-Definite Programming (SDP) methods. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 227 KiB

Open AccessProceeding Paper

Entropic Analysis of the Quantum Oscillator with a Minimal Length

by David Puertas-Centeno and Mariela Portesi

Proceedings 2019, 12(1), 57; https://doi.org/10.3390/proceedings2019012057 - 19 Nov 2019

Viewed by 1037

Abstract

The well-known Heisenberg–Robertson uncertainty relation for a pair of noncommuting observables, is expressed in terms of the product of variances and the commutator among the operators, computed for the quantum state of a system. Different modified commutation relations have been considered in the [...] Read more.

The well-known Heisenberg–Robertson uncertainty relation for a pair of noncommuting observables, is expressed in terms of the product of variances and the commutator among the operators, computed for the quantum state of a system. Different modified commutation relations have been considered in the last years with the purpose of taking into account the effect of quantum gravity. Indeed it can be seen that letting

[X, P] = i ℏ (1 + β P^{2})

implies the existence of a minimal length proportional to

\sqrt{β}

. The Bialynicki-Birula–Mycielski entropic uncertainty relation in terms of Shannon entropies is also seen to be deformed in the presence of a minimal length, corresponding to a strictly positive deformation parameter

β

. Generalized entropies can be implemented. Indeed, results for the sum of position and (auxiliary) momentum Rényi entropies with conjugated indices have been provided recently for the ground and first excited state. We present numerical findings for conjugated pairs of entropic indices, for the lowest lying levels of the deformed harmonic oscillator system in 1D, taking into account the position distribution for the wavefunction and the actual momentum. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

4 pages, 1749 KiB

Open AccessProceeding Paper

Squeezing-Enhanced Phase-Shift-Keyed Binary Communication in Noisy Channels

by Giovanni Chesi, Stefano Olivares and Matteo G. A. Paris

Proceedings 2019, 12(1), 58; https://doi.org/10.3390/proceedings2019012058 - 25 Nov 2019

Cited by 1 | Viewed by 970

Abstract

We address the use of squeezing in binary phase-shift-keyed (PSK) channels at fixed energy. In particular, we assess homodyne receivers against the Helstrom bound in the presence of phase noise. We also take into account possible imperfections in the generation of squeezing and [...] Read more.

We address the use of squeezing in binary phase-shift-keyed (PSK) channels at fixed energy. In particular, we assess homodyne receivers against the Helstrom bound in the presence of phase noise. We also take into account possible imperfections in the generation of squeezing and the effect of losses during propagation. We find that squeezing is a useful resource if its amplitude is below a given threshold depending on the energy of the signals and on the properties of the channel. Squeezing enhancement is present also when phase-noise becomes large. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

4 pages, 315 KiB

Open AccessProceeding Paper

A Numerically Exact Method for Dissipative Dynamics of Qubits

by L. M. Cangemi, G. Passarelli, V. Cataudella, P. Lucignano and G. De Filippis

Proceedings 2019, 12(1), 59; https://doi.org/10.3390/proceedings2019012059 - 4 Dec 2019

Viewed by 1115

Abstract

We propose a numerical technique suitable for simulating the dynamics of reduced density matrix of a qubit interacting with its environment. Our approach, based on a combination of short-iterative Lanczos method (SIL) and a flexible truncation scheme, allows to include in the physical [...] Read more.

We propose a numerical technique suitable for simulating the dynamics of reduced density matrix of a qubit interacting with its environment. Our approach, based on a combination of short-iterative Lanczos method (SIL) and a flexible truncation scheme, allows to include in the physical description multiple-excitation processes, beyond weak coupling and Markov approximations. We perform numerical simulations of two different model Hamiltonians, that are relevant in the field of adiabatic quantum computation (AQC), and we show that our technique is able to recover the correct thermodynamic behavior of the qubit-bath system, from weak to intermediate coupling regime. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

5 pages, 341 KiB

Open AccessProceeding Paper

Charger-Mediated Quantum Batteries

by Gian Marcello Andolina, Donato Farina, Andrea Mari, Marco Polini and Vittorio Giovannetti

Proceedings 2019, 12(1), 60; https://doi.org/10.3390/proceedings2019012060 - 6 Jul 2021

Viewed by 1857

Abstract

We study energy-transfer processes from a given quantum system, termed charger, to another one, i.e., the proper battery both in a closed and in an open quantum setting. We quantify the fraction

E_{B} (τ)

of energy stored in the [...] Read more.

We study energy-transfer processes from a given quantum system, termed charger, to another one, i.e., the proper battery both in a closed and in an open quantum setting. We quantify the fraction

E_{B} (τ)

of energy stored in the battery that can be extracted in order to perform thermodynamic work. We show that there can be a substantial gap between the average energy and the extractable work due to correlations created by charger–battery interactions. Full article

(This article belongs to the Proceedings of 11th Italian Quantum Information Science conference (IQIS2018))

► Show Figures

Figure 1

Journal Menu

Journal Browser

Proceedings, 2019, IQIS 2018

11th Italian Quantum Information Science Conference

Editorial

Other

Further Information

Guidelines

MDPI Initiatives

Follow MDPI