An Experimental Test of Envariance

TL;DR

This paper experimentally tests envariance, a symmetry in quantum entangled states, using photon pairs, and finds that real quantum states are highly envariant but not perfectly so, due to less-than-maximal entanglement.

Contribution

It provides the first experimental benchmark of envariance in quantum states, quantifying how closely real states approximate this symmetry.

Findings

Quantum states are 99.66% envariant by fidelity

Quantum states are 99.963% envariant by Bhattacharya Coefficient

Deviations from perfect envariance are due to less-than-maximal entanglement

Abstract

Envariance, or environment-assisted invariance, is a recently identified symmetry for maximally entangled states in quantum theory with important ramifications for quantum measurement, specifically for understanding Born's rule. We benchmark the degree to which nature respects this symmetry by using entangled photon pairs. Our results show quantum states can be 99.66(4)% envariant as measured using the quantum fidelity, and 99.963(5)% as measured using a modified Bhattacharya Coefficient, as compared with a perfectly envariant system which would be 100% in either measure. The deviations can be understood by the less-than-maximal entanglement in our photon pairs.