Nonlocality of a single photon: paths to an EPR-steering experiment

TL;DR

This paper explores the possibility of demonstrating EPR-steering with a single photon, analyzing previous experiments and proposing conditions under which a rigorous demonstration could be achieved.

Contribution

It provides a theoretical analysis of EPR-steering with a single photon and identifies experimental improvements needed for a rigorous demonstration.

Findings

Previous experiments do not meet the bounds for EPR-steering

Modest experimental improvements could enable EPR-steering demonstration

Adding photon counting measurements is crucial for a rigorous test

Abstract

A single photon incident on a beam splitter produces an entangled field state, and in principle could be used to violate a Bell-inequality, but such an experiment (without post-selection) is beyond the reach of current experiments. Here we consider the somewhat simpler task of demonstrating EPR-steering with a single photon (also without post-selection). That is, of demonstrating that Alice's choice of measurement on her "half" of a single photon can affect the other "half" of the photon in Bob's lab, in a sense rigorously defined by us and Doherty [Phys. Rev. Lett. 98, 140402 (2007)]. Previous work by Lvovsky and co-workers [Phys. Rev. Lett. 92, 047903 (2004)] has addressed this phenomenon (which they called "remote preparation") experimentally using homodyne measurements on a single photon. Here we show that, unfortunately, their experimental parameters do not meet the bounds necessary for a rigorous demonstration of EPR-steering with a single photon. However, we also show that modest improvements in the experimental parameters, and the addition of photon counting to the arsenal of Alice's measurements, would be sufficient to allow such a demonstration.