10,937 research outputs found
Apply current exponential de Finetti theorem to realistic quantum key distribution
In the realistic quantum key distribution (QKD), Alice and Bob respectively
get a quantum state from an unknown channel, whose dimension may be unknown.
However, while discussing the security, sometime we need to know exact
dimension, since current exponential de Finetti theorem, crucial to the
information-theoretical security proof, is deeply related with the dimension
and can only be applied to finite dimensional case. Here we address this
problem in detail. We show that if POVM elements corresponding to Alice and
Bob's measured results can be well described in a finite dimensional subspace
with sufficiently small error, then dimensions of Alice and Bob's states can be
almost regarded as finite. Since the security is well defined by the smooth
entropy, which is continuous with the density matrix, the small error of state
actually means small change of security. Then the security of
unknown-dimensional system can be solved. Finally we prove that for heterodyne
detection continuous variable QKD and differential phase shift QKD, the
collective attack is optimal under the infinite key size case.Comment: 11 pages, 2 figures, detailed version, applications adde
Stability of Phase-modulated Quantum Key Distribution System
Phase drift and random fluctuation of interference visibility in double
unbalanced M-Z QKD system are observed and distinguished. It has been found
that the interference visibilities are influenced deeply by the disturbance of
transmission fiber. Theory analysis shows that the fluctuation is derived from
the envioronmental disturbance on polarization characteristic of fiber,
especially including transmission fiber. Finally, stability conditions of
one-way anti-disturbed M-Z QKD system are given out, which provides a
theoretical guide in pragmatic anti-disturbed QKD.Comment: 9 pages, 3 figue
Security proof of differential phase shift quantum key distribution in the noiseless case
Differential phase shift quantum key distribution systems have a high
potential for achieving high speed key generation. However, its unconditional
security proof is still missing, even though it has been proposed for many
years. Here, we prove its security against collective attacks with a weak
coherent light source in the noiseless case (i.e. no bit error). The only
assumptions are that quantum theory is correct, the devices are perfect and
trusted and the key size is infinite. Our proof works on threshold detectors.
We compute the lower bound of the secret key generation rate using the
information-theoretical security proof method. Our final result shows that the
lower bound of the secret key generation rate per pulse is linearly
proportional to the channel transmission probability if Bob's detection counts
obey the binomial distribution.Comment: Published version, 13 pages, 4 figures, minor changes, references
added, acknowledgement adde
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