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Updated: Jun 28, 2026
07:56
A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
Retrocausal Capacity of a Quantum Channel: Communicating through Noisy Closed Timelike Curves
Kaiyuan Ji1,2, Seth Lloyd2, Mark M Wilde1
1Cornell University, School of Electrical and Computer Engineering, Ithaca, New York 14850, USA.
Physical Review Letters
|June 26, 2026
Summary
This study explores retrocausal communication via quantum channels, enabling information transfer backward in time. Researchers defined capacities for this process, linking them to established information measures.
Area of Science:
- Quantum Information Theory
- Theoretical Physics
- Communication Systems
Background:
- Retrocausal communication, transmitting information backward in time, is explored through quantum channels.
- Noisy postselected closed timelike curves mathematically model this quantum channel.
- Understanding information-theoretic limits is crucial for advanced communication and physics models.
Purpose of the Study:
- To characterize the one-shot retrocausal quantum and classical capacities of a quantum channel.
- To establish a novel operational interpretation for information measures like max-information and Doeblin information.
- To generalize these findings beyond quantum channels to completely positive maps.
Main Methods:
- Mathematical modeling of a noisy postselected closed timelike curve as a quantum channel.
- Complete characterization of one-shot retrocausal quantum and classical capacities.
- Analysis of asymptotic capacities in relation to max-information and regularized Doeblin information.
Main Results:
- One-shot retrocausal quantum and classical capacities are fully characterized.
- Asymptotic capacities are shown to equal the average and sum of max-information and regularized Doeblin information, respectively.
- The characterization is generalizable to all completely positive maps.
Conclusions:
- Established novel operational interpretations for max-information and regularized Doeblin information.
- Provided information-theoretic limits for retrocausal communication through quantum channels and related mechanisms.
- Implications extend to black-hole final-state models and teleportation-like processes with arbitrary boundary conditions.
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