Secret key capacity of the thermal-loss channel: Improving the lower bound

Abstract

We consider the secret key capacity of the thermal loss channel, which is modeled by a beam splitter mixing an input signal mode with an environmental thermal mode. This capacity is the maximum value of secret bits that two remote parties can generate by means of the most general adaptive protocols assisted by unlimited and two-way classical communication. To date, only upper and lower bounds are known. The present work improves the lower bound by resorting to Gaussian protocols based on suitable trusted-noise detectors.

10 pages, 2 figures

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• Maximum tolerable excess noise in continuous-variable quantum key distribution and improved lower bound on two-way capacities
• Improving the lower bound to the secret-key capacity of the thermal amplifier channel
• Optical fibres with memory effects and their quantum communication capacities
• Bicommutant categories from conformal nets