1,422 research outputs found
Evolution of locally excited avalanches in semiconductors
We show that semiconductor avalanche photodiodes can exhibit diminutive
amplification noise during the early evolution of avalanches. The noise is so
low that the number of locally excited charges that seed each avalanche can be
resolved. These findings constitute an important first step towards realization
of a solid-state noiseless amplifier. Moreover, we believe that the
experimental setup used, \textit{i.e.}, time-resolving locally excited
avalanches, will become a useful tool for optimizing the number resolution
Efficient photon number detection with silicon avalanche photodiodes
We demonstrate an efficient photon number detector for visible wavelengths
using a silicon avalanche photodiode. Under subnanosecond gating, the device is
able to resolve up to four photons in an incident optical pulse. The detection
efficiency at 600 nm is measured to be 73.8%, corresponding to an avalanche
probability of 91.1% of the absorbed photons, with a dark count probability
below 1.1x10^{-6} per gate. With this performance and operation close to room
temperature, fast-gated silicon avalanche photodiodes are ideal for optical
quantum information processing that requires single-shot photon number
detection
Continuous operation of high bit rate quantum key distribution
We demonstrate a quantum key distribution with a secure bit rate exceeding 1
Mbit/s over 50 km fiber averaged over a continuous 36-hours period. Continuous
operation of high bit rates is achieved using feedback systems to control path
length difference and polarization in the interferometer and the timing of the
detection windows. High bit rates and continuous operation allows finite key
size effects to be strongly reduced, achieving a key extraction efficiency of
96% compared to keys of infinite lengths.Comment: four pages, four figure
Probing higher order correlations of the photon field with photon number resolving avalanche photodiodes
We demonstrate the use of two high speed avalanche photodiodes in exploring
higher order photon correlations. By employing the photon number resolving
capability of the photodiodes the response to higher order photon coincidences
can be measured. As an example we show experimentally the sensitivity to higher
order correlations for three types of photon sources with distinct photon
statistics. This higher order correlation technique could be used as a low cost
and compact tool for quantifying the degree of correlation of photon sources
employed in quantum information science
Avoiding the Detector Blinding Attack on Quantum Cryptography
We show the detector blinding attack by Lydersen et al [1] will be
ineffective on most single photon avalanche photodiodes (APDs) and certainly
ineffective on any detectors that are operated correctly. The attack is only
successful if a redundant resistor is included in series with the APD, or if
the detector discrimination levels are set inappropriately
Directly phase-modulated light source
The art of imparting information onto a light wave by optical signal modulation is fundamental to all forms of optical communication. Among many schemes, direct modulation of laser diodes stands out as a simple, robust, and cost-effective method. However, the simultaneous changes in intensity, frequency, and phase have prevented its application in the field of secure quantum communication. Here, we propose and experimentally demonstrate a directly phase-modulated light source which overcomes the main disadvantages associated with direct modulation and is suitable for diverse applications such as coherent communications and quantum cryptography. The source separates the tasks of phase preparation and pulse generation between a pair of semiconductor lasers leading to very pure phase states. Moreover, the cavity-enhanced electro-optic effect enables the first example of subvolt half-wave phase modulation at high signal rates. The source is compact, stable, and versatile, and we show its potential to become the standard transmitter for future quantum communication networks based on attenuated laser pulses
Best-Practice Criteria for Practical Security of Self-Differencing Avalanche Photodiode Detectors in Quantum Key Distribution
Fast gated avalanche photodiodes (APDs) are the most commonly used single
photon detectors for high bit rate quantum key distribution (QKD). Their
robustness against external attacks is crucial to the overall security of a QKD
system or even an entire QKD network. Here, we investigate the behavior of a
gigahertz-gated, self-differencing InGaAs APD under strong illumination, a
tactic Eve often uses to bring detectors under her control. Our experiment and
modelling reveal that the negative feedback by the photocurrent safeguards the
detector from being blinded through reducing its avalanche probability and/or
strengthening the capacitive response. Based on this finding, we propose a set
of best-practice criteria for designing and operating fast-gated APD detectors
to ensure their practical security in QKD
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Gigahertz-gated InGaAs/InP single-photon detector with detection efficiency exceeding 55% at 1550 nm
We report on a gated single-photon detector based on InGaAs/InP avalanche
photodiodes (APDs) with a single-photon detection efficiency exceeding 55% at
1550 nm. Our detector is gated at 1 GHz and employs the self-differencing
technique for gate transient suppression. It can operate nearly dead time free,
except for the one clock cycle dead time intrinsic to self-differencing, and we
demonstrate a count rate of 500 Mcps. We present a careful analysis of the
optimal driving conditions of the APD measured with a dead time free detector
characterization setup. It is found that a shortened gate width of 360 ps
together with an increased driving signal amplitude and operation at higher
temperatures leads to improved performance of the detector. We achieve an
afterpulse probability of 7% at 50% detection efficiency with dead time free
measurement and a record efficiency for InGaAs/InP APDs of 55% at an afterpulse
probability of only 10.2% with a moderate dead time of 10 ns.L. C. Comandar acknowledges personal support via the EPSRC funded CDT in Photonics System Development.This is the author accepted manuscript. The final version is available via AIP at http://scitation.aip.org/content/aip/journal/jap/117/8/10.1063/1.4913527
Best-Practice Criteria for Practical Security of Self-Differencing Avalanche Photodiode Detectors in Quantum Key Distribution
Fast-gated avalanche photodiodes (APDs) are the most commonly used single photon detectors for high-bit-rate quantum key distribution (QKD). Their robustness against external attacks is crucial to the overall security of a QKD system, or even an entire QKD network. We investigate the behavior of a gigahertz-gated, self-differencing (In,Ga)As APD under strong illumination, a tactic Eve often uses to bring detectors under her control. Our experiment and modeling reveal that the negative feedback by the photocurrent safeguards the detector from being blinded through reducing its avalanche probability and/or strengthening the capacitive response. Based on this finding, we propose a set of best-practice criteria for designing and operating fast-gated APD detectors to ensure their practical security in QKD
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Quantum cryptography without detector vulnerabilities using optically-seeded lasers
© 2016 Macmillan Publishers Limited. All rights reserved. Security in quantum cryptography is continuously challenged by inventive attacks targeting the real components of a cryptographic set-up, and duly restored by new countermeasures to foil them. Owing to their high sensitivity and complex design, detectors are the most frequently attacked components. It was recently shown that two-photon interference from independent light sources can be used to remove any vulnerability from detectors. This new form of detection-safe quantum key distribution (QKD), termed measurement-device-independent (MDI), has been experimentally demonstrated but with modest key rates. Here, we introduce a new pulsed laser seeding technique to obtain high-visibility interference from gain-switched lasers and thereby perform MDI-QKD with unprecedented key rates in excess of 1 megabit per second in the finite-size regime. This represents a two to six orders of magnitude improvement over existing implementations and supports the new scheme as a practical resource for secure quantum communications.L. C. Comandar acknowledges personal support via the EPSRC funded CDT in Photonic Systems Development and Toshiba Research Europe Ltd
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