Quantum nonlocality without entanglement in a pair of qubits

TL;DR

This paper investigates the limits of local operations and classical communication in distinguishing certain quantum states, revealing a fundamental gap in success probabilities even with separable measurements.

Contribution

It demonstrates that even separable measurements cannot match the success probability of global measurements in certain quantum state discrimination tasks.

Findings

Global measurements outperform separable measurements in success probability.

Separable measurements cannot achieve the same success probability as global measurements.

A nonzero gap exists between local and global measurement success probabilities.

Abstract

We consider unambiguous discrimination of two separable bipartite states, one being pure and the other being a rank-2 mixed state. There is a gap between the optimal success probability under global measurements and the one achieved by generalized measurements with separable measurement operators. We show that even the latter success probability cannot be achieved via local operations and classical communication, leaving a nonzero gap in between.