Strong Einstein-Podolsky-Rosen steering with unconditional entangled states

TL;DR

This paper demonstrates a significant enhancement of EPR-steering effects using unconditional entangled states, achieving a low conditional variance product suitable for practical quantum communication and sensing applications.

Contribution

The study reports a sixfold increase in EPR-steering effect with an unprecedented low variance product on unconditional two-mode-squeezed states, advancing quantum steering research.

Findings

Observed a conditional variance product of about 0.04, well below the steering threshold of 1.

Achieved high interference contrast suitable for quantum networks.

State contained less than 8% vacuum contribution, including detection imperfections.

Abstract

In 1935 Schr\"odinger introduced the terms entanglement and steering in the context of the famous gedanken experiment discussed by Einstein, Podolsky, and Rosen (EPR). Here, we report on a sixfold increase of the observed EPR-steering effect as quantified by the Reid-criterion. We achieved an unprecedented low conditional variance product of about 0.04 < 1, where 1 is the upper bound below which steering is present. The steering effect was observed on an unconditional two-mode-squeezed entangled state that contained a total vacuum state contribution of less than 8%, including detection imperfections. Together with the achieved high interference contrast between the entangled state and a bright coherent laser field, our state is compatible with efficient applications in high-power laser interferometers and fiber-based networks for entanglement distribution.