Experimental demonstration of counterfactual quantum communication

TL;DR

This paper experimentally demonstrates counterfactual quantum communication, showing it can be implemented over a 1 km fiber with high visibility and low error rate, indicating potential for long-distance secure quantum communication.

Contribution

First faithful experimental implementation of counterfactual quantum communication with on-table and fiber-based setups at telecom wavelength.

Findings

High interferometer visibility (>98%) maintained with active stabilization.

Achieved quantum bit error rate around 5.5% over 1 km fiber.

Feasibility of extending counterfactual communication to long distances.

Abstract

Based on principle of quantum mechanics, quantum cryptography provides an intriguing way to establish secret keys between remote parties, generally relying on actual transmission of signal particles. Surprisingly, an even more striking method is recently proposed by Noh named as `counterfactual quantum cryptography' enabling key distribution, in which particles carrying secret information are seemly not being transmitted through quantum channel. We experimentally give here a faithful implementation by following the scheme with an on-table realization. Furthermore, we report an illustration on a 1 km fiber operating at telecom wavelength to verify its feasibility for extending to long distance. For both cases, high visibilities of better than 98% are maintained with active stabilization of interferometers, while a quantum bit error rate around 5.5% is attained after 1 km channel.