Counterfactual communication without a trace in the transmission channel

TL;DR

This paper demonstrates an improved counterfactual communication protocol that effectively leaves no environmental trace in the transmission channel, verified through frequency tagging, and successfully transmits an image with high fidelity.

Contribution

The authors experimentally realize a modified counterfactual communication protocol that eliminates environmental traces, strengthening the claim of counterfactuality compared to previous methods.

Findings

No frequency shift detected in transmitted photons

Successfully transmitted a quick response code image

Protocol leaves no detectable environmental trace

Abstract

We report an experimental realization of a modified counterfactual communication protocol that eliminates the dominant environmental trace left by photons passing through the transmission channel. Compared to Wheeler's criterion for inferring past particle paths, as used in prior protocols, our trace criterion provide stronger support for the claim of the counterfactuality of the communication. We verify the lack of trace left by transmitted photons via tagging the propagation arms of an interferometric device by distinct frequency-shifts and finding that the collected photons have no frequency shift which corresponds to the transmission channel. As a proof of principle, we counterfactually transfer a quick response code image with sufficient fidelity to be scanned with a cell phone.