When the pigeon and the letter do not travel together

In standard communication the pigeon always carries the message; the information is linked to a physical entity/particle. Counter to intuition, in a new counterfactual communication protocol published in NPJ Quantum Information, scientists from the University of Vienna, the University of Cambridge and the MIT have experimentally demonstrated that in quantum mechanics this is not always true, thereby contradicting a crucial premise of communication theory. Whether it is pigeons in the air, electrons in a telegraph wire, radio waves from a cell phone or single photons in an optical fiber, in standard communication, there is always a particle or wave involved in the information exchange between two parties; say Alice and Bob. However, in quantum mechanics, one can send information from Alice to Bob while the particle or wave involved in this information exchange travels from Bob to Alice. In an international collaboration led by Philip Walther, scientist from the University of Vienna teamed up with the University of Cambridge and the Massachusetts Institute of Technology to implement a new counterfactual communication protocol. In standard photonic communication, the information is encoded in single photons; thus, the information and the single photons travel in the same direction. However, in counterfactual communication there is no carrier found travelling in the same direction as the message. In this implementation, single photons would travel from Alice to Bob while information would travel from Bob to Alice. What carries the message then?