Retrocausal capacity of a quantum channel

• URL: http://arxiv.org/abs/2509.08965v1
• Date: Wed, 10 Sep 2025 19:53:23 GMT
• Title: Retrocausal capacity of a quantum channel
• Abstract summary: We study the capacity of a quantum channel for retrocausal communication, where messages are transmitted backward in time.<n>We show that the corresponding capacities are equal to the average and sum, respectively, of the channel's max-information and its regularized Doeblin information.
• Score: 12.220177153326562
• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: We study the capacity of a quantum channel for retrocausal communication, where messages are transmitted backward in time, from a sender in the future to a receiver in the past, through a noisy postselected closed timelike curve (P-CTC) represented by the channel. We completely characterize the one-shot retrocausal quantum and classical capacities of a quantum channel, and we show that the corresponding asymptotic capacities are equal to the average and sum, respectively, of the channel's max-information and its regularized Doeblin information. This endows these information measures with a novel operational interpretation. Furthermore, our characterization can be generalized beyond quantum channels to all completely positive maps. This imposes information-theoretic limits on transmitting messages via postselected-teleportation-like mechanisms with arbitrary initial- and final-state boundary conditions, including those considered in various black-hole final-state models.

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