Unbounded entanglement-sustaining sequential local quantum state discrimination

TL;DR

This paper introduces a protocol for distinguishing two orthogonal entangled two-qubit states through sequential local operations, maintaining finite entanglement at each step and achieving high success probability.

Contribution

It presents a novel method that allows multiple parties to distinguish entangled states locally while preserving entanglement, unlike previous approaches that destroy it.

Findings

Success probability can approach unity for many state sets.

Finite entanglement is retained at each discrimination step.

The protocol outperforms random guessing in success rate.

Abstract

Two pure orthogonal quantum states can be perfectly distinguished by sequential local action of multiple pairs of parties. However, this process typically leads to the complete dissolution of entanglement in the states being discriminated. We propose a protocol that allows an arbitrary number of pairs of parties to distinguish between any two orthogonal, entangled, two-qubit pure states using local quantum operations and classical communication, with a success probability greater than that of random guessing, while ensuring that at each step, the individual ensemble states retain a finite amount of entanglement. Our protocol employs the minimum-error state discrimination approach. For demonstrating the retention of entanglement in the ensemble states at each step, we use logarithmic negativity as well as the concept of entanglement witnessing. For a large family of sets of the two states, the success probability of discrimination can be as close as required to unity, while sustaining a finite amount of entanglement in each step.