Abstract
If two identical copies of a completely depolarizing channel are put into a superposition of their possible causal orders, they can transmit nonzero classical information. Here we study how well we can transmit classical information with depolarizing channels put in superposition of causal orders via a quantum switch. We calculate the Holevo quantity if the superposition uses only cyclic permutations of channels and find that it increases with and it is independent of . For a qubit it never reaches 1 if we are increasing . On the other hand, the classical capacity decreases with the dimension of the message system. Further, for and 4 we studied the superposition of all causal orders and uniformly superposed causal orders belonging to different cosets created by a cyclic permutation subgroup.
1 More- Received 28 April 2021
- Accepted 2 June 2021
DOI:https://doi.org/10.1103/PhysRevA.103.062610
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