Nonclassical traits in multi-copy state discrimination

TL;DR

This paper investigates multi-copy quantum state discrimination, revealing nonclassical traits and outperforming classical strategies, with implications for nonlocality without entanglement and operational bounds.

Contribution

It introduces a comparison of quantum and classical multi-copy state discrimination, identifying nonlocality without entanglement and bounds for bit-like theories.

Findings

A qubit strategy outperforms all bit strategies.

Certain operational theories outperform quantum strategies even with classical measurements.

Instances of nonlocality without entanglement are identified.

Abstract

Quantum state discrimination is a fundamental information processing task that serves as a building block for numerous applications and provides implications at the foundational level. In this work, we consider minimum error discrimination of multi-copy states, where instead of preparing a single system we assume that multiple instances of the same state are prepared. Now the discrimination allows for measurements from multiple parties with different measurement strategies varying from global measurement strategy to ones restricted to different forms of local operations and classical communication strategies. By comparing the average success probabilities in quantum and classical cases, we find a qubit strategy that outperforms all the bit strategies. However, we find that there are other bit-like operational theories which can outperform the best qubit strategies even with a classical measurement strategy and we are able to identify instances of different theories where different measurement strategies are optimal. In this way, we are able to find instances of nonlocality without entanglement as well as provide general bounds for bit-like operational theories.