Universal Optimal Quantum Correlator

TL;DR

This paper introduces a universal, optimal scheme for measuring quantum correlation functions using ancillary systems, applicable with current quantum optical technology and useful for testing uncertainty relations.

Contribution

It presents a new realization scheme called partial expectation values that implements a previously proposed strategy for accessing quantum correlation functions.

Findings

Scheme is universal and independent of rho, A, and B.

It is optimal in a statistical sense.

Compatible with current quantum optical technology.

Abstract

Recently, a novel operational strategy to access quantum correlation functions of the form Tr[A rho B] was provided in [F. Buscemi, M. Dall'Arno, M. Ozawa, and V. Vedral, arXiv:1312.4240]. Here we propose a realization scheme, that we call partial expectation values, implementing such strategy in terms of a unitary interaction with an ancillary system followed by the measurement of an observable on the ancilla. Our scheme is universal, being independent of rho, A, and B, and it is optimal in a statistical sense. Our scheme is suitable for implementation with present quantum optical technology, and provides a new way to test uncertainty relations.