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arXiv · 2401.15634

Quantum communication on the bosonic loss-dephasing channel

Francesco Anna Mele·Farzin Salek·Vittorio Giovannetti·Ludovico Lami
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Abstract

Quantum optical systems are typically affected by two types of noise: photon loss and dephasing. Despite extensive research on each noise process individually, a comprehensive understanding of their combined effect is still lacking. A crucial problem lies in determining the values of loss and dephasing for which the resulting loss-dephasing channel is anti-degradable, implying the absence of codes capable of correcting its effect or, alternatively, capable of enabling quantum communication. A conjecture in [Quantum 6, 821 (2022)] suggested that the bosonic loss-dephasing channel is anti-degradable if and only if the loss is above $50\%$. In this paper we refute this conjecture, specifically proving that for any value of the loss, if the dephasing is above a critical value, then the bosonic loss-dephasing channel is anti-degradable. While our result identifies a large parameter region where quantum communication is not possible, we also prove that if two-way classical communication is available, then quantum communication -- and thus quantum key distribution -- is always achievable, even for high values of loss and dephasing.

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Francesco Anna Mele, Farzin Salek, Vittorio Giovannetti, Ludovico Lami. 2024-01-28. Quantum communication on the bosonic loss-dephasing channel. https://doi.org/10.1103/physreva.110.012460

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