Direct measurement of a nonlocal entangled quantum state

TL;DR

This paper introduces a novel method to directly measure the nonlocal wave function of a bipartite quantum system using Modular Values, demonstrated experimentally with hyper-entangled photon pairs.

Contribution

It is the first to propose and experimentally implement a method for directly measuring nonlocal wave functions using Modular Values.

Findings

Successful experimental measurement of nonlocal wave function

First demonstration of direct measurement of nonlocal entanglement

Method applicable to hyper-entangled photon states

Abstract

Entanglement and wave function description are two of the core concepts that make quantum mechanics such a unique theory. A method to directly measure the wave function, using Weak Values, was demonstrated by Lundeen et al., Nature \textbf{474}, 188(2011). However, it is not applicable to a scenario of two disjoint systems, where nonlocal entanglement can be a crucial element since that requires obtaining the Weak Values of nonlocal observables. Here, for the first time, we propose a method to directly measure a nonlocal wave function of a bipartite system, using Modular Values. The method is experimentally implemented for a photon pair in a hyper-entangled state, i.e. entangled both in polarization and momentum degrees of freedom.