Quantum communication on the bosonic loss-dephasing channel

• URL: http://arxiv.org/abs/2401.15634v3
• Date: Thu, 25 Jul 2024 14:53:18 GMT
• Title: Quantum communication on the bosonic loss-dephasing channel
• Authors: Francesco Anna Mele, Farzin Salek, Vittorio Giovannetti, Ludovico Lami,
• Abstract summary: A crucial problem lies in determining the values of loss and dephasing for which the resulting loss-dephasing channel is anti-degradable. We prove that for any value of the loss, if the dephasing is above a critical value, then the bosonic loss-dephasing channel is anti-degradable.
• Score: 7.824710236769593
• License: http://creativecommons.org/licenses/by/4.0/
• 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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