Nowadays there are many different ways to communicate. One thing common to all those methods, from carrier pigeon to email, is that the transmission of information requires sending the physical system that represents it from one party to another. If Bob wants to send a message to Alice, then photons, sound waves, pigeons, or some other information-carrying entities need to make the trip. Information is an abstract mathematical concept, but as Rolf Landauer famously pointed out, there is no information without representation.
In the quantum world, however, another option exists: Bob can send a message to Alice, via a kind of carrier pigeon, without having the pigeon actually fly between them. The weird scenario is appropriately called counterfactual communication.
In a recent paper in Proceedings of the National Academy of Sciences, a group headed by Jian-Wei Pan at the University of Science and Technology of China reported an experimental demonstration of counterfactual communication. The researchers sent data with single photons, but the photons did not fly through the communication channel.
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