57,497 research outputs found
The Wiretap Channel with Feedback: Encryption over the Channel
In this work, the critical role of noisy feedback in enhancing the secrecy
capacity of the wiretap channel is established. Unlike previous works, where a
noiseless public discussion channel is used for feedback, the feed-forward and
feedback signals share the same noisy channel in the present model. Quite
interestingly, this noisy feedback model is shown to be more advantageous in
the current setting. More specifically, the discrete memoryless modulo-additive
channel with a full-duplex destination node is considered first, and it is
shown that the judicious use of feedback increases the perfect secrecy capacity
to the capacity of the source-destination channel in the absence of the
wiretapper. In the achievability scheme, the feedback signal corresponds to a
private key, known only to the destination. In the half-duplex scheme, a novel
feedback technique that always achieves a positive perfect secrecy rate (even
when the source-wiretapper channel is less noisy than the source-destination
channel) is proposed. These results hinge on the modulo-additive property of
the channel, which is exploited by the destination to perform encryption over
the channel without revealing its key to the source. Finally, this scheme is
extended to the continuous real valued modulo- channel where it is
shown that the perfect secrecy capacity with feedback is also equal to the
capacity in the absence of the wiretapper.Comment: Submitted to IEEE Transactions on Information Theor
Continuous-variable entanglement distillation over a pure loss channel with multiple quantum scissors
Entanglement distillation is a key primitive for distributing high-quality
entanglement between remote locations. Probabilistic noiseless linear
amplification based on the quantum scissors is a candidate for entanglement
distillation from noisy continuous-variable (CV) entangled states. Being a
non-Gaussian operation, quantum scissors is challenging to analyze. We present
a derivation of the non-Gaussian state heralded by multiple quantum scissors in
a pure loss channel with two-mode squeezed vacuum input. We choose the reverse
coherent information (RCI)---a proven lower bound on the distillable
entanglement of a quantum state under one-way local operations and classical
communication (LOCC), as our figure of merit. We evaluate a Gaussian lower
bound on the RCI of the heralded state. We show that it can exceed the
unlimited two-way LOCCassisted direct transmission entanglement distillation
capacity of the pure loss channel. The optimal heralded Gaussian RCI with two
quantum scissors is found to be significantly more than that with a single
quantum scissors, albeit at the cost of decreased success probability. Our
results fortify the possibility of a quantum repeater scheme for CV quantum
states using the quantum scissors.Comment: accepted for publication in Physical Review
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