11,907 research outputs found
Effect of detector dead-times on the security evaluation of differential-phase-shift quantum key distribution against sequential attacks
We investigate limitations imposed by detector dead-times on the performance
of sequential attacks against a differential-phase-shift (DPS) quantum key
distribution (QKD) protocol with weak coherent pulses. In particular, we
analyze sequential attacks based on unambiguous state discrimination of the
signal states emitted by the source and we obtain ultimate upper bounds on the
maximal distance achievable by a DPS QKD scheme both in the so-called trusted
and untrusted device scenarios, respectively.Comment: 21 pages, 14 figure
Practical long-distance quantum key distribution system using decoy levels
Quantum key distribution (QKD) has the potential for widespread real-world
applications. To date no secure long-distance experiment has demonstrated the
truly practical operation needed to move QKD from the laboratory to the real
world due largely to limitations in synchronization and poor detector
performance. Here we report results obtained using a fully automated, robust
QKD system based on the Bennett Brassard 1984 protocol (BB84) with low-noise
superconducting nanowire single-photon detectors (SNSPDs) and decoy levels.
Secret key is produced with unconditional security over a record 144.3 km of
optical fibre, an increase of more than a factor of five compared to the
previous record for unconditionally secure key generation in a practical QKD
system.Comment: 9 page
Experimental quantum key distribution with source flaws
Decoy-state quantum key distribution (QKD) is a standard technique in current
quantum cryptographic implementations. Unfortunately, existing experiments have
two important drawbacks: the state preparation is assumed to be perfect without
errors and the employed security proofs do not fully consider the finite-key
effects for general attacks. These two drawbacks mean that existing experiments
are not guaranteed to be secure in practice. Here, we perform an experiment
that for the first time shows secure QKD with imperfect state preparations over
long distances and achieves rigorous finite-key security bounds for decoy-state
QKD against coherent attacks in the universally composable framework. We
quantify the source flaws experimentally and demonstrate a QKD implementation
that is tolerant to channel loss despite the source flaws. Our implementation
considers more real-world problems than most previous experiments and our
theory can be applied to general QKD systems. These features constitute a step
towards secure QKD with imperfect devices.Comment: 12 pages, 4 figures, updated experiment and theor
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