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Power of Sequential Protocols in Hidden Quantum Channel Discrimination
Sho Sugiura1,2, Arkopal Dutt3, William J Munro4,5
1Physics and Informatics Laboratory, NTT Research, Inc., 940 Stewart Drive, Sunnyvale, California, 94085, USA.
Abstract:
In many natural and engineered systems, unknown quantum channels act on a subsystem that cannot be directly controlled and measured, but is instead learned through a controllable subsystem that weakly interacts with it. We study quantum channel discrimination (QCD) under these restrictions, which we call hidden system QCD. We find sequential protocols achieve perfect discrimination and saturate the Heisenberg limit. In contrast, depth-1 parallel and multishot protocols cannot solve hidden system QCD. This suggests sequential protocols are superior in experimentally realistic situations.
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