66 research outputs found
A high-speed multi-protocol quantum key distribution transmitter based on a dual-drive modulator
We propose a novel source based on a dual-drive modulator that is adaptable
and allows Alice to choose between various practical quantum key distribution
(QKD) protocols depending on what receiver she is communicating with.
Experimental results show that the proposed transmitter is suitable for
implementation of the Bennett and Brassard 1984 (BB84), coherent one-way (COW)
and differential phase shift (DPS) protocols with stable and low quantum bit
error rate. This could become a useful component in network QKD, where
multi-protocol capability is highly desirable.Comment: 15 pages, 7 figure
Absolute calibration of fiber-coupled single-photon detector
We show a setup for characterising the efficiency of a single-photon-detector
absolutely and with a precision better of 1%. Since the setup does not rely on
calibrated devices and can be implemented with standard-optic components, it
can be realised in any laboratory. Our approach is based on an
Erbium-Doped-Fiber-Amplifier (EDFA) radiometer as a primary measurement
standard for optical power, and on an ultra-stable source of spontaneous
emission. As a proof of principle, we characterise the efficiency of an
InGaAs/InP single-photon detector. We verified the correctness of the
characterisation with independent measurements. In particular, the measurement
of the optical power made with the EDFA radiometer has been compared to that of
the Swiss Federal Office of Metrology using a transfer power meter. Our
approach is suitable for frequent characterisations of high-efficient
single-photon detectors.Comment: 14 pages, 4 figure
Free-running InGaAs single photon detector with 1 dark count per second at 10% efficiency
We present a free-running single photon detector for telecom wavelengths
based on a negative feedback avalanche photodiode (NFAD). A dark count rate as
low as 1 cps was obtained at a detection efficiency of 10%, with an afterpulse
probability of 2.2% for 20 {\mu}s of deadtime. This was achieved by using an
active hold-off circuit and cooling the NFAD with a free-piston stirling cooler
down to temperatures of -110C. We integrated two detectors into a
practical, 625 MHz clocked quantum key distribution system. Stable, real-time
key distribution in presence of 30 dB channel loss was possible, yielding a
secret key rate of 350 bps.Comment: 4 pages, 4 figure
Afterpulsing studies of low noise InGaAs/InP single-photon negative feedback avalanche diodes
We characterize the temporal evolution of the afterpulse probability in a
free-running negative feedback avalanche diode (NFAD) over an extended range,
from 300 ns to 1 ms. This is possible thanks to an extremely low
dark count rate on the order of 1 cps at 10% efficiency, achieved by operating
the NFAD at a temperatures as low as 143 K. Experimental results in a large
range of operating temperatures (223-143 K) are compared with a legacy
afterpulsing model based on multiple trap families at discrete energy levels,
which is found to be lacking in physical completeness. Subsequently, we expand
on a recent proposal which considers a continuous spectrum of traps by
introducing well defined edges to the spectrum, which are experimentally
observed.Comment: 9 pages, 5 figure
Detector-Device-Independent Quantum Key Distribution
Recently, a quantum key distribution (QKD) scheme based on entanglement
swapping, called measurement-device-independent QKD (mdiQKD), was proposed to
bypass all detector side-channel attacks. While mdiQKD is conceptually elegant
and offers a supreme level of security, the experimental complexity is
challenging for practical systems. For instance, it requires interference
between two widely separated independent single-photon sources, and the rates
are dependent on detecting two photons - one from each source. Here we
experimentally demonstrate a QKD scheme that removes the need for a two-photon
system and instead uses the idea of a two-qubit single-photon (TQSP) to
significantly simplify the implementation and improve the efficiency of mdiQKD
in several aspects.Comment: 5 pages + 3 figure
Detector-device-independent QKD: security analysis and fast implementation
One of the most pressing issues in quantum key distribution (QKD) is the
problem of detector side- channel attacks. To overcome this problem,
researchers proposed an elegant "time-reversal" QKD protocol called
measurement-device-independent QKD (MDI-QKD), which is based on time-reversed
entanglement swapping. However, MDI-QKD is more challenging to implement than
standard point- to-point QKD. Recently, an intermediary QKD protocol called
detector-device-independent QKD (DDI-QKD) has been proposed to overcome the
drawbacks of MDI-QKD, with the hope that it would eventually lead to a more
efficient detector side-channel-free QKD system. Here, we analyze the security
of DDI-QKD and elucidate its security assumptions. We find that DDI-QKD is not
equivalent to MDI-QKD, but its security can be demonstrated with reasonable
assumptions. On the more practical side, we consider the feasibility of DDI-QKD
and present a fast experimental demonstration (clocked at 625 MHz), capable of
secret key exchange up to more than 90 km.Comment: 9 pages, 4 figure
High-detection efficiency and low-timing jitter with amorphous superconducting nanowire single-photon detectors
Recent progress in the development of superconducting nanowire single-photon
detectors (SNSPDs) made of amorphous material has delivered excellent
performances, and has had a great impact on a range of research fields. Despite
showing the highest system detection efficiency (SDE) ever reported with
SNSPDs, amorphous materials typically lead to lower critical currents, which
impacts on their jitter performance. Combining a very low jitter and a high SDE
remains a challenge. Here, we report on highly efficient superconducting
nanowire single-photon detectors based on amorphous MoSi, combining system
jitters as low as 26 ps and a SDE of 80% at 1550 nm. We also report detailed
observations on the jitter behaviour, which hints at intrinsic limitations and
leads to practical implications for SNSPD performance
Demonstration of a Thermally Coupled Row-Column SNSPD Imaging Array
While single-pixel superconducting nanowire single photon detectors (SNSPDs) have demonstrated remarkable efficiency and timing performance from the UV to near-IR, scaling these devices to large imaging arrays remains challenging. Here, we propose a new SNSPD multiplexing system using thermal coupling and detection correlations between two photosensitive layers of an array. Using this architecture with the channels of one layer oriented in rows and the second layer in columns, we demonstrate imaging capability in 16-pixel arrays with accurate spot tracking at the few-photon level. We also explore the performance trade-offs of orienting the top layer nanowires parallel and perpendicular to the bottom layer. The thermally coupled row-column scheme is readily able to scale to the kilopixel size with existing readout systems and, when combined with other multiplexing architectures, has the potential to enable megapixel scale SNSPD imaging arrays
Provably Secure and Practical Quantum Key Distribution over 307 km of Optical Fibre
Proposed in 1984, quantum key distribution (QKD) allows two users to exchange
provably secure keys via a potentially insecure quantum channel. Since then,
QKD has attracted much attention and significant progress has been made in both
theory and practice. On the application front, however, the operating distance
of practical fibre-based QKD systems is limited to about 150 km, which is
mainly due to the high background noise produced by commonly used semiconductor
single-photon detectors (SPDs) and the stringent demand on the minimum
classical- post-processing (CPP) block size. Here, we present a compact and
autonomous QKD system that is capable of distributing provably-secure
cryptographic key over 307 km of ultra-low-loss optical fibre (51.9 dB loss).
The system is based on a recently developed standard semiconductor (inGaAs)
SPDs with record low background noise and a novel efficient finite-key security
analysis for QKD. This demonstrates the feasibility of practical long-distance
QKD based on standard fibre optic telecom components.Comment: 6+7 pages, 3 figure
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