We report on a photodetector in which colloidal quantum dots directly bridge nanometer-spaced ele... more We report on a photodetector in which colloidal quantum dots directly bridge nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film photodetectors, charge mobility no longer plays a role in our quantum-dot junctions as charge extraction requires only two individual tunnel events. We find an efficient photoconductive gain mechanism with external quantum efficiencies of 38 electrons-per-photon in combination with response times faster than 300 ns. This compact device-architecture may open up new routes for improved photodetector performance in which efficiency and bandwidth do not go at the cost of one another.
A bright photon source that combines high-fidelity entanglement, on-demand generation, high extra... more A bright photon source that combines high-fidelity entanglement, on-demand generation, high extraction efficiency, directional and coherent emission, as well as position control at the nanoscale is required for implementing ambitious schemes in quantum information processing, such as that of a quantum repeater. Still, all of these properties have not yet been achieved in a single device. Semiconductor quantum dots embedded in nanowire waveguides potentially satisfy all of these requirements; however, although theoretically predicted, entanglement has not yet been demonstrated for a nanowire quantum dot. Here, we demonstrate a bright and coherent source of strongly entangled photon pairs from a position-controlled nanowire quantum dot with a fidelity as high as 0.859±0.006 and concurrence of 0.80±0.02. The two-photon quantum state is modified via the nanowire shape. Our new nanoscale entangled photon source can be integrated at desired positions in a quantum photonic circuit, single-...
Physics and Simulation of Optoelectronic Devices XXI, 2013
ABSTRACT Single quantum dots embedded in tapered nanowire waveguides have emerged as leading cand... more ABSTRACT Single quantum dots embedded in tapered nanowire waveguides have emerged as leading candidates for designing high efficiency single-photon and entangled photon sources, with efficiencies exceeding 90%. Here we have developed a bottom-up growth approach that allows for independent control of boththe quantum dot size, and position, as well as the nanowire shape. Importantly, by design, the single quantum dot is always found perfectly on the nanowire axis. By integrating a gold mirror at the base of a tapered nanowire waveguide we obtain a 20-fold enhancement in the single-photon flux in comparison to no waveguide. The 20-fold enhancement is accompanied by a shortening of the exciton lifetime as the quantum emitter couples to the fundamental waveguide mode with an increased rate. Finally, the optical quality of the emitter is drastically improved by removing the nanowire stacking faults in the vicinity of the quantum dot. As a result, we demonstrate very pure single-photon emission with a probability of multi-photon emission below 1%, and an emission line width that is reduced by at least an order of magnitude (<30 μeV) as compared to when stacking faults were present in the nanowire (as high as 10-100 per micron). The demonstrated brightness of our single-photon source (42 % efficiency), combined with the very pure single photon emission and high spectral purity is encouraging in development of future quantum technologies based on nanowires, such as interfacing remote quantum bits or constructing a secure quantum network.
abstract Active depth imaging approaches are being used in a number of emerging applications, for... more abstract Active depth imaging approaches are being used in a number of emerging applications, for example in environmental sensing, manufacturing and defense. The high sensitivity and picosecond timing resolution of the time-correlated single-photon counting ...
We report optical experiments of a charge tunable, single nanowire quantum dot subject to an elec... more We report optical experiments of a charge tunable, single nanowire quantum dot subject to an electric field tuned by two independent voltages. First, we control tunneling events through an applied electric field along the nanowire growth direction. Second, we modify the chemical potential in the nanowire with a back-gate. We combine these two field-effects to isolate a single electron and independently tune the tunnel coupling of the quantum dot with the contacts. Such charge control is a first requirement for opto-electrical single electron spin experiments on a nanowire quantum dot.
Nanowire-superlattices with different structural phases along the nanowire direction, such as wur... more Nanowire-superlattices with different structural phases along the nanowire direction, such as wurtzite (WZ) and zincblende (ZB) forms of the same compound, often exhibit a "type II" band-alignment with electrons on ZB and holes on WZ. This is a material property of most of III-V semiconductors. We show via InP nanowires that as the nanowire diameter decreases, quantum-confinement alters this basic material property, placing both electrons and holes on the same (ZB) phase. This structural design causes a dramatic increase in absorption strength and reduced radiative lifetime.
This paper highlights a significant advance in time-of-flight depth imaging: by using a scanning ... more This paper highlights a significant advance in time-of-flight depth imaging: by using a scanning transceiver which incorporated a free-running, low noise superconducting nanowire single-photon detector, we were able to obtain centimeter resolution depth images of low-signature objects in daylight at stand-off distances of the order of one kilometer at the relatively eye-safe wavelength of 1560 nm. The detector used had an efficiency of 18% at 1 kHz dark count rate, and the overall system jitter was ~100 ps. The depth images were acquired by illuminating the scene with an optical output power level of less than 250 µW average, and using per-pixel dwell times in the millisecond regime.
We report on the ultraclean emission from single quantum dots embedded in pure wurtzite nanowires... more We report on the ultraclean emission from single quantum dots embedded in pure wurtzite nanowires. Using a two-step growth process combining selective-area and vapor-liquid-solid epitaxy, we grow defect-free wurtzite InP nanowires with embedded InAsP quantum dots, which are clad to diameters sufficient for waveguiding at λ ~ 950 nm. The absence of nearby traps, at both the nanowire surface and along its length in the vicinity of the quantum dot, manifests in excitonic transitions of high spectral purity. Narrow emission line widths (30 μeV) and very-pure single photon emission with a probability of multiphoton emission below 1% are achieved, both of which were not possible in previous work where stacking fault densities were significantly higher.
We report reproducible fabrication of InP-InAsP nanowire light emitting diodes in which electron-... more We report reproducible fabrication of InP-InAsP nanowire light emitting diodes in which electron-hole recombination is restricted to a quantum-dot-sized InAsP section. The nanowire geometry naturally self-aligns the quantum dot with the n-InP and p-InP ends of the wire, making these devices promising candidates for electrically-driven quantum optics experiments. We have investigated the operation of these nano-LEDs with a consistent series
... Figure shows spectra taken on a single quantum dot, the excitation power density was adjusted... more ... Figure shows spectra taken on a single quantum dot, the excitation power density was adjusted to have only one emission line. Additional emission lines appear with increasing laser power. A spectrum taken over a larger wavelength range, which is seen in the left inset of Fig. ...
Eu 2+ -doped ZnS nanoparticles with an average size of around 3 nm were prepared, and an emission... more Eu 2+ -doped ZnS nanoparticles with an average size of around 3 nm were prepared, and an emission band around 530 nm was observed. By heating in air at 150 °C, this emission decreased, while the typical sharp line emission of Eu 3+ increased. This suggests that ...
The European Physical Journal D - Atomic, Molecular and Optical Physics, 2002
: We examine the problem of efficiently collecting the photons produced by solid-state single p... more : We examine the problem of efficiently collecting the photons produced by solid-state single photon sources. The extent of the problem is first established with the aid of simple physical concepts. Several approaches to improving the collection efficiency are then examined and are broadly categorized into two types. First are those based on cavity quantum dynamics, in which the pathways
We report on a photodetector in which colloidal quantum dots directly bridge nanometer-spaced ele... more We report on a photodetector in which colloidal quantum dots directly bridge nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film photodetectors, charge mobility no longer plays a role in our quantum-dot junctions as charge extraction requires only two individual tunnel events. We find an efficient photoconductive gain mechanism with external quantum efficiencies of 38 electrons-per-photon in combination with response times faster than 300 ns. This compact device-architecture may open up new routes for improved photodetector performance in which efficiency and bandwidth do not go at the cost of one another.
A bright photon source that combines high-fidelity entanglement, on-demand generation, high extra... more A bright photon source that combines high-fidelity entanglement, on-demand generation, high extraction efficiency, directional and coherent emission, as well as position control at the nanoscale is required for implementing ambitious schemes in quantum information processing, such as that of a quantum repeater. Still, all of these properties have not yet been achieved in a single device. Semiconductor quantum dots embedded in nanowire waveguides potentially satisfy all of these requirements; however, although theoretically predicted, entanglement has not yet been demonstrated for a nanowire quantum dot. Here, we demonstrate a bright and coherent source of strongly entangled photon pairs from a position-controlled nanowire quantum dot with a fidelity as high as 0.859±0.006 and concurrence of 0.80±0.02. The two-photon quantum state is modified via the nanowire shape. Our new nanoscale entangled photon source can be integrated at desired positions in a quantum photonic circuit, single-...
Physics and Simulation of Optoelectronic Devices XXI, 2013
ABSTRACT Single quantum dots embedded in tapered nanowire waveguides have emerged as leading cand... more ABSTRACT Single quantum dots embedded in tapered nanowire waveguides have emerged as leading candidates for designing high efficiency single-photon and entangled photon sources, with efficiencies exceeding 90%. Here we have developed a bottom-up growth approach that allows for independent control of boththe quantum dot size, and position, as well as the nanowire shape. Importantly, by design, the single quantum dot is always found perfectly on the nanowire axis. By integrating a gold mirror at the base of a tapered nanowire waveguide we obtain a 20-fold enhancement in the single-photon flux in comparison to no waveguide. The 20-fold enhancement is accompanied by a shortening of the exciton lifetime as the quantum emitter couples to the fundamental waveguide mode with an increased rate. Finally, the optical quality of the emitter is drastically improved by removing the nanowire stacking faults in the vicinity of the quantum dot. As a result, we demonstrate very pure single-photon emission with a probability of multi-photon emission below 1%, and an emission line width that is reduced by at least an order of magnitude (<30 μeV) as compared to when stacking faults were present in the nanowire (as high as 10-100 per micron). The demonstrated brightness of our single-photon source (42 % efficiency), combined with the very pure single photon emission and high spectral purity is encouraging in development of future quantum technologies based on nanowires, such as interfacing remote quantum bits or constructing a secure quantum network.
abstract Active depth imaging approaches are being used in a number of emerging applications, for... more abstract Active depth imaging approaches are being used in a number of emerging applications, for example in environmental sensing, manufacturing and defense. The high sensitivity and picosecond timing resolution of the time-correlated single-photon counting ...
We report optical experiments of a charge tunable, single nanowire quantum dot subject to an elec... more We report optical experiments of a charge tunable, single nanowire quantum dot subject to an electric field tuned by two independent voltages. First, we control tunneling events through an applied electric field along the nanowire growth direction. Second, we modify the chemical potential in the nanowire with a back-gate. We combine these two field-effects to isolate a single electron and independently tune the tunnel coupling of the quantum dot with the contacts. Such charge control is a first requirement for opto-electrical single electron spin experiments on a nanowire quantum dot.
Nanowire-superlattices with different structural phases along the nanowire direction, such as wur... more Nanowire-superlattices with different structural phases along the nanowire direction, such as wurtzite (WZ) and zincblende (ZB) forms of the same compound, often exhibit a "type II" band-alignment with electrons on ZB and holes on WZ. This is a material property of most of III-V semiconductors. We show via InP nanowires that as the nanowire diameter decreases, quantum-confinement alters this basic material property, placing both electrons and holes on the same (ZB) phase. This structural design causes a dramatic increase in absorption strength and reduced radiative lifetime.
This paper highlights a significant advance in time-of-flight depth imaging: by using a scanning ... more This paper highlights a significant advance in time-of-flight depth imaging: by using a scanning transceiver which incorporated a free-running, low noise superconducting nanowire single-photon detector, we were able to obtain centimeter resolution depth images of low-signature objects in daylight at stand-off distances of the order of one kilometer at the relatively eye-safe wavelength of 1560 nm. The detector used had an efficiency of 18% at 1 kHz dark count rate, and the overall system jitter was ~100 ps. The depth images were acquired by illuminating the scene with an optical output power level of less than 250 µW average, and using per-pixel dwell times in the millisecond regime.
We report on the ultraclean emission from single quantum dots embedded in pure wurtzite nanowires... more We report on the ultraclean emission from single quantum dots embedded in pure wurtzite nanowires. Using a two-step growth process combining selective-area and vapor-liquid-solid epitaxy, we grow defect-free wurtzite InP nanowires with embedded InAsP quantum dots, which are clad to diameters sufficient for waveguiding at λ ~ 950 nm. The absence of nearby traps, at both the nanowire surface and along its length in the vicinity of the quantum dot, manifests in excitonic transitions of high spectral purity. Narrow emission line widths (30 μeV) and very-pure single photon emission with a probability of multiphoton emission below 1% are achieved, both of which were not possible in previous work where stacking fault densities were significantly higher.
We report reproducible fabrication of InP-InAsP nanowire light emitting diodes in which electron-... more We report reproducible fabrication of InP-InAsP nanowire light emitting diodes in which electron-hole recombination is restricted to a quantum-dot-sized InAsP section. The nanowire geometry naturally self-aligns the quantum dot with the n-InP and p-InP ends of the wire, making these devices promising candidates for electrically-driven quantum optics experiments. We have investigated the operation of these nano-LEDs with a consistent series
... Figure shows spectra taken on a single quantum dot, the excitation power density was adjusted... more ... Figure shows spectra taken on a single quantum dot, the excitation power density was adjusted to have only one emission line. Additional emission lines appear with increasing laser power. A spectrum taken over a larger wavelength range, which is seen in the left inset of Fig. ...
Eu 2+ -doped ZnS nanoparticles with an average size of around 3 nm were prepared, and an emission... more Eu 2+ -doped ZnS nanoparticles with an average size of around 3 nm were prepared, and an emission band around 530 nm was observed. By heating in air at 150 °C, this emission decreased, while the typical sharp line emission of Eu 3+ increased. This suggests that ...
The European Physical Journal D - Atomic, Molecular and Optical Physics, 2002
: We examine the problem of efficiently collecting the photons produced by solid-state single p... more : We examine the problem of efficiently collecting the photons produced by solid-state single photon sources. The extent of the problem is first established with the aid of simple physical concepts. Several approaches to improving the collection efficiency are then examined and are broadly categorized into two types. First are those based on cavity quantum dynamics, in which the pathways
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Papers by Val Zwiller