Counterfactual Quantum Communication: Information Exchange in Quantum Shadows

Counterfactual quantum communication (CQC) is an intriguing paradigm originating from quantum mechanics, enabling spatially separated parties to achieve communication tasks without the need to transmit any physical particles across the channel. Conventional quantum communication typically relies on particle transmission or utilizes entanglement-assisted protocols with local operations and classical communication, such as quantum teleportation and superdense coding, to transfer information. As the research area of quantum communication is being rapidly developed, significant progress has been made in the development of CQC. In this paper, we present a comprehensive tutorial on CQC for transmitting both classical and quantum information, noting that no physical particles are found in the channel during successful information transmission. We begin by studying the origin of CQC, followed by a detailed examination of counterfactual protocols for classical and quantum information transmission. This paper highlights the applications of CQC and outlines future research directions.