Perfect discrimination of quantum measurements using entangled systems

TL;DR

This paper explores how entangled quantum systems can perfectly discriminate certain measurements that are indistinguishable with single quantum systems, revealing a fundamental advantage of entanglement in quantum measurement discrimination.

Contribution

It introduces the first formal framework for single-shot measurement discrimination using entanglement and demonstrates that entanglement enables perfect discrimination where single systems cannot.

Findings

Sets of measurements are perfectly distinguishable with entanglement but not with single systems.

Any pure two-qubit entangled state provides an advantage over one-qubit systems.

Measurement discrimination advantage is linked to EPR 'quantum steering'.

Abstract

Distinguishing physical processes is one of the fundamental problems in quantum physics. Although distinguishability of quantum preparations and quantum channels have been studied considerably, distinguishability of quantum measurements remains largely unexplored. We investigate the problem of single-shot discrimination of quantum measurements using two strategies, one based on single quantum systems and the other one based on entangled quantum systems. First, we formally define both scenarios. We then construct sets of measurements (including non-projective) in arbitrary finite dimensions that are perfectly distinguishable within the second scenario using quantum entanglement, while not in the one based on single quantum systems. Furthermore, we show that any advantage in measurement discrimination tasks over single systems is a demonstration of Einstein-Podolsky-Rosen 'quantum steering'. Alongside, we prove that all pure two-qubit entangled states provide an advantage in a measurement discrimination task over one-qubit systems.