Heralded quantum steering over a high-loss channel

TL;DR

This paper demonstrates a scheme for verifying quantum entanglement over high-loss channels using heralded quantum steering, enabling secure long-distance quantum communication despite significant signal loss.

Contribution

The authors experimentally implement a heralded quantum steering protocol that works over channels with 14.8 dB loss, equivalent to 80 km of fiber, advancing long-distance quantum communication.

Findings

Verified entanglement over 14.8 dB loss channel

Implemented event-ready quantum steering protocol

Overcame key barrier for high-loss quantum communication

Abstract

Entanglement is the key resource for many long-range quantum information tasks, including secure communication and fundamental tests of quantum physics. These tasks require robust verification of shared entanglement, but performing it over long distances is presently technologically intractable because the loss through an optical fiber or free-space channel opens up a detection loophole. We design and experimentally demonstrate a scheme that verifies entanglement in the presence of at least $14.8\pm0.1$ dB of added loss, equivalent to approximately $80$ km of telecommunication fiber. Our protocol relies on entanglement swapping to herald the presence of a photon after the lossy channel, enabling event-ready implementation of quantum steering. This result overcomes the key barrier in device-independent communication under realistic high-loss scenarios and in the realization of a quantum repeater.