Low Timing Jitter Detector for Gigahertz Quantum Key Distribution

A superconducting single-photon detector based on a niobium nitride nanowire is demonstrated in an optical-fibre-based quantum key distribution test bed operating at a clock rate of 3.3 GHz and a transmission wavelength of 850 nm. The low jitter of the detector leads to significant reduction in the estimated quantum bit error rate and a resultant improvement in the secrecy efficiency compared to previous estimates made by use of silicon single-photon avalanche detectors.Comment: 11 pages, including 2 figure

Solid immersion lens applications for nanophotonic devices

Solid immersion lens (SIL) microscopy combines the advantages of conventional microscopy with those of near-field techniques, and is being increasingly adopted across a diverse range of technologies and applications. A comprehensive overview of the state-of-the-art in this rapidly expanding subject is therefore increasingly relevant. Important benefits are enabled by SIL-focusing, including an improved lateral and axial spatial profiling resolution when a SIL is used in laser-scanning microscopy or excitation, and an improved collection efficiency when a SIL is used in a light-collection mode, for example in fluorescence micro-spectroscopy. These advantages arise from the increase in numerical aperture (NA) that is provided by a SIL. Other SIL-enhanced improvements, for example spherical-aberration-free sub-surface imaging, are a fundamental consequence of the aplanatic imaging condition that results from the spherical geometry of the SIL. Beginning with an introduction to the theory of SIL imaging, the unique properties of SILs are exposed to provide advantages in applications involving the interrogation of photonic and electronic nanostructures. Such applications range from the sub-surface examination of the complex three-dimensional microstructures fabricated in silicon integrated circuits, to quantum photoluminescence and transmission measurements in semiconductor quantum dot nanostructures

Integrated Joule switches for the control of current dynamics in parallel superconducting strips

Understanding and harnessing the physics of the dynamic current distribution in parallel superconducting strips holds the key to creating next generation sensors for single molecule and single photon detection. Non-uniformity in the current distribution in parallel superconducting strips leads to low detection efficiency and unstable operation, preventing the scale up to large area sensors. Recent studies indicate that non-uniform current distributions occurring in parallel strips can be understood and modeled in the framework of the generalized London model. Here we build on this important physical insight, investigating an innovative design with integrated superconducting-to-resistive Joule switches to break the superconducting loops between the strips and thus control the current dynamics. Employing precision low temperature nano-optical techniques, we map the uniformity of the current distribution before- and after the resistive strip switching event, confirming the effectiveness of our design. These results provide important insights for the development of next generation large area superconducting strip-based sensors

On-chip quantum interference between silicon photon-pair sources

Large-scale integrated quantum photonic technologies1, 2 will require on-chip integration of identical photon sources with reconfigurable waveguide circuits. Relatively complex quantum circuits have been demonstrated already1, 2, 3, 4, 5, 6, 7, but few studies acknowledge the pressing need to integrate photon sources and waveguide circuits together on-chip8, 9. A key step towards such large-scale quantum technologies is the integration of just two individual photon sources within a waveguide circuit, and the demonstration of high-visibility quantum interference between them. Here, we report a silicon-on-insulator device that combines two four-wave mixing sources in an interferometer with a reconfigurable phase shifter. We configured the device to create and manipulate two-colour (non-degenerate) or same-colour (degenerate) path-entangled or path-unentangled photon pairs. We observed up to 100.0 ± 0.4% visibility quantum interference on-chip, and up to 95 ± 4% off-chip. Our device removes the need for external photon sources, provides a path to increasing the complexity of quantum photonic circuits and is a first step towards fully integrated quantum technologies

Resonance fluorescence from a telecom-wavelength quantum dot

© 2016 Author(s).We report on resonance fluorescence from a single quantum dot emitting at telecom wavelengths. We perform high-resolution spectroscopy and observe the Mollow triplet in the Rabi regime - a hallmark of resonance fluorescence. The measured resonance-fluorescence spectra allow us to rule out pure dephasing as a significant decoherence mechanism in these quantum dots. Combined with numerical simulations, the experimental results provide robust characterisation of charge noise in the environment of the quantum dot. Resonant control of the quantum dot opens up new possibilities for the on-demand generation of indistinguishable single photons at telecom wavelengths as well as quantum optics experiments and direct manipulation of solid-state qubits in telecom-wavelength quantum dots

Heralding of telecommunication photon pairs with a superconducting single photon detector

Experiments involving entangled photon pairs created via spontaneous parametric down conversion typically use wavelengths in the visible regime. The extension of a photonic quantum information link to a fiber optical network requires that entangled pairs be created at telecommunication wavelengths (1550 nm), for which photon counting detector technology is inferior to visible detection, in particular, low coincidence detection rates of correlated-photon pairs. We demonstrate a correlated-photon pair measurement using the superconducting single photon detector in a heralding scheme that can be used to substantially improve the correlated-photon detection rate

Quantum key distribution at 1550 nm with twin superconducting single-photon detectors

The authors report on the full implementation of a superconducting detector technology in a fiber-based quantum key distribution (QKD) link. Nanowire-based superconducting single-photon detectors (SSPDs) offer infrared single-photon detection with low dark counts, low jitter, and short recovery times. These detectors are highly promising candidates for future high key rate QKD links operating at 1550 nm. The authors use twin SSPDs to perform the BB84 protocol in a 1550 nm fiber-based QKD link clocked at 3.3 MHz. They exchange secure key over a distance of 42.5 km in telecom fiber and demonstrate that secure key can be transmitted over a total link loss exceeding 12 dB

Quantum dot single photon sources studied with superconducting single photon detectors

We report the observation of photon antibunching from a single, self-assembled InGaAs quantum dot (QD) at temperatures up to 135 K. The second-order intensity correlation, <formula formulatype="inline"><tex>$g^{(2)}$</tex> </formula>(0), is less than 0.260 <formula formulatype="inline"><tex>$pm$</tex></formula> 0.024 for temperatures up to 100 K. At 120 K, <formula formulatype="inline"><tex>$g^{(2)}$</tex></formula>(0) increases to about 0.471, which is slightly less than the second-order intensity correlation expected from two independent single emitters. In addition, we characterize the performance of a superconducting single photon detector (SSPD) based on a nanopatterned niobium nitride wire that exhibits 68 <formula formulatype="inline"><tex>$pm$</tex></formula> 3-ps timing jitter and less than 100-Hz dark count rate with a detection efficiency (DE) of up to 2% at 902 nm. This detector is used to measure spontaneous emission lifetimes of semiconductor quantum wells (QWs) emitting light at wavelengths of 935 and 1245 nm. The sensitivity to wavelengths longer than 1 <formula formulatype="inline"><tex>$mu$</tex></formula>m and the Gaussian temporal response of this superconducting detector present clear advantages over the conventional detector technologies. We also use this detector to characterize the emission from a single InGaAs QD embedded in a micropillar cavity, measuring a spontaneous emission lifetime of 370 ps and a <formula formulatype="inline"><tex>$g^{(2)}$</tex> </formula>(0) of 0.24 <formula formulatype="inline"><tex>$pm$</tex></formula> 0.03