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Proceedings Paper

Probing the quantum depolarizing channel with mixed Indefinite causal order
Author(s): Michael Frey
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Paper Abstract

Indefinite causal ordering (ICO) refers to quantum channels arranged so that the path through them is a super- position of different possible paths. The ICO is called pure when the path superposition is a pure quantum state. Channel probing, in which probes in prepared quantum states are passed through copies of the channel to estimate one or more channel parameters, is aided by ICO. Specifically, pure ICO is known to increase the quantum Fisher information (QFI) in the processed probe state about the unknown parameter(s). We consider the case complementary to pure ICO in which the path state is maximally mixed for a given indefiniteness. Deriving the QFI under this condition by a new approach, we find that mixed ICO-assisted probing, while not as beneficial as pure ICO probing, still yields greater QFI than does the comparable scheme with definite causal order. The d-dimensional quantum depolarizing channel is used as the channel model for this study. While mixed ICO-assisted probing, like pure ICO-assisted probing, is generally advantageous for probing the depolarizing channel, mixed ICO's relative effectiveness decreases with probe dimension, just as for pure ICO-assisted probing, each being most effective for qubit probes.

Paper Details

Date Published: 13 May 2019
PDF: 8 pages
Proc. SPIE 10984, Quantum Information Science, Sensing, and Computation XI, 109840D (13 May 2019); doi: 10.1117/12.2520395
Show Author Affiliations
Michael Frey, National Institute of Standards and Technology (United States)

Published in SPIE Proceedings Vol. 10984:
Quantum Information Science, Sensing, and Computation XI
Eric Donkor; Michael Hayduk; Michael R. Frey; Samuel J. Lomonaco Jr.; John M. Myers, Editor(s)

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