21 research outputs found
Detector dead-time effects and paralyzability in high-speed quantum key distribution
Recent advances in quantum key distribution (QKD) have given rise to systems
that operate at transmission periods significantly shorter than the dead times
of their component single-photon detectors. As systems continue to increase in
transmission rate, security concerns associated with detector dead times can
limit the production rate of sifted bits. We present a model of high-speed QKD
in this limit that identifies an optimum transmission rate for a system with
given link loss and detector response characteristics
Harnessing high-dimensional hyperentanglement through a biphoton frequency comb
Quantum entanglement is a fundamental resource for secure information
processing and communications, where hyperentanglement or high-dimensional
entanglement has been separately proposed towards high data capacity and error
resilience. The continuous-variable nature of the energy-time entanglement
makes it an ideal candidate for efficient high-dimensional coding with minimal
limitations. Here we demonstrate the first simultaneous high-dimensional
hyperentanglement using a biphoton frequency comb to harness the full potential
in both energy and time domain. The long-postulated Hong-Ou-Mandel quantum
revival is exhibited, with up to 19 time-bins, 96.5% visibilities. We further
witness the high-dimensional energy-time entanglement through Franson revivals,
which is observed periodically at integer time-bins, with 97.8% visibility.
This qudit state is observed to simultaneously violate the generalized Bell
inequality by up to 10.95 deviations while observing recurrent
Clauser-Horne-Shimony-Holt S-parameters up to 2.76. Our biphoton frequency comb
provides a platform in photon-efficient quantum communications towards the
ultimate channel capacity through energy-time-polarization high-dimensional
encoding
A Nanocryotron Ripple Counter Integrated with a Superconducting Nanowire Single-Photon Detector for Megapixel Arrays
Decreasing the number of cables that bring heat into the cryocooler is a
critical issue for all cryoelectronic devices. Especially, arrays of
superconducting nanowire single-photon detectors (SNSPDs) could require more
than readout lines. Performing signal processing operations at low
temperatures could be a solution. Nanocryotrons, superconducting nanowire
three-terminal devices, are good candidates for integrating sensing and
electronics on the same technological platform as SNSPDs in photon-counting
applications. In this work, we demonstrated that it is possible to read out,
process, encode, and store the output of SNSPDs using exclusively
superconducting nanowires. In particular, we present the design and development
of a nanocryotron ripple counter that detects input voltage spikes and converts
the number of pulses to an -digit value. The counting base can be tuned from
2 to higher values, enabling higher maximum counts without enlarging the
circuit. As a proof-of-principle, we first experimentally demonstrated the
building block of the counter, an integer- frequency divider with
ranging from 2 to 5. Then, we demonstrated photon-counting operations at
405\,nm and 1550\,nm by coupling an SNSPD with a 2-digit nanocryotron counter
partially integrated on-chip. The 2-digit counter operated in either base 2 or
base 3 with a bit error rate lower than and a maximum count
rate of s. We simulated circuit architectures for
integrated readout of the counter state, and we evaluated the capabilities of
reading out an SNSPD megapixel array that would collect up to counts
per second. The results of this work, combined with our recent publications on
a nanocryotron shift register and logic gates, pave the way for the development
of nanocryotron processors, from which multiple superconducting platforms may
benefit
High Efficiency Planar Geometry Germanium-on-silicon Single-photon Avalanche Diode Detectors
This paper presents the performance of 26 μm and 50 μm diameter planar Ge-on-Si single-photon avalanche diode (SPAD) detectors. The addition of germanium in these detectors extends the spectral range into the short-wave infrared (SWIR) region, beyond the capability of already well-established Si SPAD devices. There are several advantages for extending the spectral range into the SWIR region including: reduced eye-safety laser threshold, greater attainable ranges, and increased depth resolution in range finding applications, in addition to the enhanced capability to image through obscurants such as fog and smoke. The time correlated single-photon counting (TCSPC) technique has been utilized to observe record low dark count rates, below 100 kHz at a temperature of 125 K for up to a 6.6 % excess bias, for the 26 μm diameter devices. Under identical experimental conditions, in terms of excess bias and temperature, the 50 μm diameter device consistently demonstrates dark count rates a factor of 4 times greater than 26 μm diameter devices, indicating that the dark count rate is proportional to the device volume. Single-photon detection efficiencies of up to ~ 29 % were measured at a wavelength of 1310 nm at 125 K. Noise equivalent powers (NEP) down to 9.8 × 10-17 WHz-1/2 and jitters < 160 ps are obtainable, both significantly lower than previous 100 μm diameter planar geometry devices, demonstrating the potential of these devices for highly sensitive and high-speed imaging in the SWIR
Photon-efficient quantum key distribution using time–energy entanglement with high-dimensional encoding
Conventional quantum key distribution (QKD) typically uses binary encoding based on photon polarization or time-bin degrees of freedom and achieves a key capacity of at most one bit per photon. Under photon-starved conditions the rate of detection events is much lower than the photon generation rate, because of losses in long distance propagation and the relatively long recovery times of available single-photon detectors. Multi-bit encoding in the photon arrival times can be beneficial in such photon-starved situations. Recent security proofs indicate high-dimensional encoding in the photon arrival times is robust and can be implemented to yield high secure throughput. In this work we demonstrate entanglement-based QKD with high-dimensional encoding whose security against collective Gaussian attacks is provided by a high-visibility Franson interferometer. We achieve unprecedented key capacity and throughput for an entanglement-based QKD system because of four principal factors: Franson interferometry that does not degrade with loss; error correction coding that can tolerate high error rates; optimized time–energy entanglement generation; and highly efficient WSi superconducting nanowire single-photon detectors. The secure key capacity yields as much as 8.7 bits per coincidence. When optimized for throughput we observe a secure key rate of 2.7 Mbit s[superscript −1] after 20 km fiber transmission with a key capacity of 6.9 bits per photon coincidence. Our results demonstrate a viable approach to high-rate QKD using practical photonic entanglement and single-photon detection technologies.United States. Army Research Office (Defense Advanced Research Projects Agency. Information in a Photon (InPho) Program Grant W911NF-10-1-0416