Experimental EPR-Steering of Bell-local States

TL;DR

This paper experimentally demonstrates EPR-steering in Bell-local mixed entangled states using multiple measurement settings, showing increased robustness to noise compared to previous two-setting approaches.

Contribution

It introduces an experimental method with more than two measurement settings to observe EPR-steering in Bell-local states, expanding the understanding of quantum correlations.

Findings

EPR-steering occurs in Bell-local states with multiple measurement settings.

Increasing measurement settings enhances robustness against noise.

First experimental demonstration of EPR-steering in Bell-local mixed states.

Abstract

Entanglement is the defining feature of quantum mechanics, and understanding the phenomenon is essential at the foundational level and for future progress in quantum technology. The concept of steering was introduced in 1935 by Schr\"odinger as a generalization of the Einstein-Podolsky-Rosen (EPR) paradox. Surprisingly, it has only recently been formalized as a quantum information task with arbitrary bipartite states and measurements, for which the existence of entanglement is necessary but not sufficient. Previous experiments in this area have been restricted to the approach of Reid [PRA 40, 913], which followed the original EPR argument in considering only two different measurement settings per side. Here we implement more than two settings so as to be able to demonstrate experimentally, for the first time, that EPR-steering occurs for mixed entangled states that are Bell-local (that is, which cannot possibly demonstrate Bell-nonlocality). Unlike the case of Bell inequalities, increasing the number of measurement settings beyond two--we use up to six--dramatically increases the robustness of the EPR-steering phenomenon to noise.