27 research outputs found
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BB84 and DQPS-QKD experiments using one polarization-insensitive measurement setup with a countermeasure against detector blinding and control attacks
Scalable implementation of mutually unbiased bases for -dimensional quantum key distribution
A high-dimensional quantum key distribution (QKD) can improve error rate
tolerance and the secret key rate. Many -dimensional QKDs have used two
mutually unbiased bases (MUBs), while MUBs enable a more robust QKD.
However, a scalable implementation has not been achieved because the setups
have required devices even for two MUBs or a flexible convertor for a
specific optical mode. Here, we propose a scalable and general implementation
of MUBs using interferometers in prime power dimensions
. We implemented the setup for time-bin states and observed an average
error rate of 3.8% for phase bases, which is lower than the 23.17% required for
a secure QKD against collective attack in .Comment: 6 pages, 3 figures, followed by Supplemental Material of 8 pages, 1
figure, 1 tabl
Generation of a time-bin Greenberger--Horne--Zeilinger state with an optical switch
Multipartite entanglement is a critical resource in quantum information
processing that exhibits much richer phenomenon and stronger correlations than
in bipartite systems. This advantage is also reflected in its multi-user
applications. Although many demonstrations have used photonic polarization
qubits, polarization-mode dispersion confines the transmission of photonic
polarization qubits through an optical fiber. Consequently, time-bin qubits
have a particularly important role to play in quantum communication systems.
Here, we generate a three-photon time-bin Greenberger-Horne-Zeilinger (GHZ)
state using a 2 x 2 optical switch as a time-dependent beam splitter to
entangle time-bin Bell states from a spontaneous parametric down-conversion
source and a weak coherent pulse. To characterize the three-photon time-bin GHZ
state, we performed measurement estimation, showed a violation of the Mermin
inequality, and used quantum state tomography to fully reconstruct a density
matrix, which shows a state fidelity exceeding 70%. We expect that our
three-photon time-bin GHZ state can be used for long-distance multi-user
quantum communication.Comment: 8 pages, 4 figures, 1 tabl
10-GHz-clock time-multiplexed non-degenerate optical parametric oscillator network with a variable planar lightwave circuit interferometer
A coherent XY machine (CXYM) is a physical spin simulator that can simulate
the XY model by mapping XY spins onto the continuous phases of non-degenerate
optical parametric oscillators (NOPOs). Here, we demonstrated a large-scale
CXYM with >47,000 spins by generating 10-GHz-clock time-multiplexed NOPO pulses
via four-wave mixing in a highly nonlinear fiber inside a fiber ring cavity. By
implementing a unidirectional coupling from the i-th pulse to the (i+1)-th
pulse with a variable 1-pulse delay planar lightwave circuit interferometer, we
successfully controlled the effective temperature of a one-dimensional XY spin
network within two orders of magnitude.Comment: 5 pages, 4 figure
Quantum key distribution over 40 dB channel loss using superconducting single photon detectors
Quantum key distribution (QKD) offers an unconditionally secure means of
communication based on the laws of quantum mechanics. Currently, a major
challenge is to achieve a QKD system with a 40 dB channel loss, which is
required if we are to realize global scale QKD networks using communication
satellites. Here we report the first QKD experiment in which secure keys were
distributed over 42 dB channel loss and 200 km of optical fibre. We employed
the differential phase shift quantum key distribution (DPS-QKD) protocol
implemented with a 10-GHz clock frequency, and superconducting single photon
detectors (SSPD) based on NbN nanowire. The SSPD offers a very low dark count
rate (a few Hz) and small timing jitter (60 ps full width at half maximum).
These characteristics allowed us to construct a 10-GHz clock QKD system and
thus distribute secure keys over channel loss of 42 dB. In addition, we
achieved a 17 kbit/s secure key rate over 105 km of optical fibre, which is two
orders of magnitude higher than the previous record, and a 12.1 bit/s secure
key rate over 200 km of optical fibre, which is the longest terrestrial QKD yet
demonstrated. The keys generated in our experiment are secure against both
general collective attacks on individual photons and a specific collective
attack on multi-photons, known as a sequential unambiguous state discrimination
(USD) attack.Comment: 15 pages, 5 figures. Original versio
Performance of various quantum key distribution systems using 1.55 um up-conversion single-photon detectors
We compare the performance of various quantum key distribution (QKD) systems
using a novel single-photon detector, which combines frequency up-conversion in
a periodically poled lithium niobate (PPLN) waveguide and a silicon avalanche
photodiode (APD). The comparison is based on the secure communication rate as a
function of distance for three QKD protocols: the Bennett-Brassard 1984 (BB84),
the Bennett, Brassard, and Mermin 1992 (BBM92), and the coherent differential
phase shift keying (DPSK). We show that the up-conversion detector allows for
higher communication rates and longer communication distances than the commonly
used InGaAs/InP APD for all the three QKD protocols.Comment: 9 pages, 9 figure