Maximum tolerable excess noise in CV-QKD and improved lower bound on
two-way capacities
- URL: http://arxiv.org/abs/2303.12867v3
- Date: Thu, 4 May 2023 10:32:00 GMT
- Title: Maximum tolerable excess noise in CV-QKD and improved lower bound on
two-way capacities
- Authors: Francesco Anna Mele, Ludovico Lami, Vittorio Giovannetti
- Abstract summary: We find a new lower bound on the energy-constrained and unconstrained two-way quantum and secret-key capacities of all phase-insensitive bosonic Gaussian channels.
Ours is the first nonzero lower bound on the two-way quantum capacity in the parameter range where the (reverse) coherent information becomes negative.
- Score: 8.808993671472349
- License: http://creativecommons.org/licenses/by/4.0/
- Abstract: The two-way capacities of quantum channels determine the ultimate
entanglement and secret-key distribution rates achievable by two distant
parties that are connected by a noisy transmission line, in absence of quantum
repeaters. Since repeaters will likely be expensive to build and maintain, a
central open problem of quantum communication is to understand what
performances are achievable without them. In this paper, we find a new lower
bound on the energy-constrained and unconstrained two-way quantum and
secret-key capacities of all phase-insensitive bosonic Gaussian channels,
namely thermal attenuator, thermal amplifier, and additive Gaussian noise,
which are realistic models for the noise affecting optical fibres or free-space
links. Ours is the first nonzero lower bound on the two-way quantum capacity in
the parameter range where the (reverse) coherent information becomes negative,
and it shows explicitly that entanglement distribution is always possible when
the channel is not entanglement breaking. This completely solves a crucial open
problem of the field, namely, establishing the maximum excess noise which is
tolerable in continuous-variable quantum key distribution. In addition, our
construction is fully explicit, i.e. we devise and optimise a concrete
entanglement distribution and distillation protocol that works by combining
recurrence and hashing protocols
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