Detecting Multipartite Classical States and their Resemblances

TL;DR

This paper investigates multipartite states near the quantum-classical boundary, introducing generalized-classical states and providing methods to detect classicality using analytic criteria and semi-definite programming algorithms.

Contribution

It introduces the concept of generalized-classical states allowing for NDLID with general measurements and offers practical detection methods including an SDP algorithm.

Findings

Analytic criterion for classical states

Semi-definite programming for generalized-classical states

Detection methods applicable to quantum and signal processing contexts

Abstract

We study various types of multipartite states lying near the quantum-classical boundary. The class of so-called classical states are precisely those in which each party can perform a projective measurement to identify a locally held state without disturbing the global state, a task known as non-disruptive local state identification (NDLID). We introduce a new class of states called generalized-classical states which allow for NDLID when the most general quantum measurements are permitted. A simple analytic method as well as a physical criterion are presented for detecting whether a multipartite state is classical. To decide whether a state is generalized-classical, we provide a semi-definite programming algorithm which can be adapted for use in other unrelated contexts such as signal processing.