Demonstration of quantum-limited discrimination of multicopy pure versus mixed states

Arunkumar Jagannathan, Michael Grace, Olivia Brasher, Jeffrey H. Shapiro, Saikat Guha, Jonathan L. Habif

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


We demonstrate an optical receiver that achieves the quantum Chernoff bound for discriminating coherent states from thermal states in the multicopy scenario. In contrast, we find that repeated use of the receiver approaching the Helstrom bound for single-copy measurement is suboptimal in this multicopy case. Furthermore, for a large class of multicopy discrimination tasks between a pure and a mixed state, we prove that any Helstrom-bound achieving single-copy receiver is suboptimal by a factor of at least 2 in error-probability exponent compared to the multicopy quantum Chernoff bound. This behavior has a classical analog in the performance gap between soft-decision and hard-decision receivers for detecting a multicopy signal embedded in white Gaussian noise.

Original languageEnglish (US)
Article number032446
JournalPhysical Review A
Issue number3
StatePublished - Mar 2022

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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