Counterfactual communication protocols

          @misc{ scivideos_PIRSA:18070056,
            doi = {10.48660/18070056},
            url = {https://pirsa.org/18070056},
            author = {Vaidman, Lev},
            keywords = {Quantum Foundations},
            language = {en},
            title = {Counterfactual  communication protocols},
            publisher = {Perimeter Institute for Theoretical Physics},
            year = {2018},
            month = {aug},
            note = {PIRSA:18070056 see, \url{https://scivideos.org/pirsa/18070056}}
          }
          

Abstract

Possibility to communicate between spatially separated regions, without even a single photon passing between the two parties, is an amazing quantum phenomenon. The possibility of transmitting one value of a bit in such a way, the interaction-free measurement, was known for quarter of a century. The protocols of full communication, including transmitting unknown quantum states were proposed only few years ago, but it was shown that in all these protocols the particle was leaving a weak trace in the transmission channel, the trace larger than the trace left by a single particle passing through the channel. However, a simple modification of these recent protocols eliminates the trace in the transmission channel and makes all these protocols truly counterfactual.