Quantum information processing in Fock space

© Lorenzo Nocchi

Generally speaking, communication is the process of transmitting a message (information) from a sender to a receiver. We usually think of sending physical information, i.e. a message embodied in an information carrier and sent as a signal, such as voltage signals, speech, video or radar. In the classical world, physical systems that carry information obey the laws of classical physics. For example, electromagnetic signals propagate in space according to Maxwell’s equations, thus the speed of information transfer is fundamentally limited to that of light. Similarly, in radio communications, information flows from a radio emitter to the radio receiver but not vice-versa, as it follows from the causality principle. In other words, abilities and limitations of communication and information processing in general are governed by the laws of physics. From that perspective, quantum physics together with its counterintuitive principles allows for novel possibilities that are not permissible in classical world. Encoding, transmitting and decoding information carried by quantum systems enables distant parties to beat the limits fundamentally imposed by the laws of classical physic.

In our recent work [SD17] we have studied the model of limited communication, i.e. the communication restricted to a) a finite number of information carriers, and b) finite speed of propagation. When the distant parties use a single classical particle to communicate, they are restricted to “one-way signaling”, as the particle can carry information in one direction only. We analyzed the corresponding quantum scenario, where the parties communicate via a single quantum particle prepared in superposition of different spatial locations. We have shown that such a scenario results in “two-way signaling”, which is impossible in classical physics (visit here for the media coverage). Our framework does not assume (a priori) the use of quantum entanglement, in contrast to majority of known quantum information tasks and protocols. Such a phenomenon is essentially enabled by the “particle-vacuum” entanglement, which is an intrinsic feature of the Fock space. In a subsequent work [MMD+18], we have shown that such entanglement can be used for secure and anonymous communication. These results indicate that information-processing in Fock space can offer novel possibilities. Our main goal is continue the investigation in this direction with the main focus on quantum communication in Fock space.


[SD16] F. del Santo and B. Dakić, Two-way communication with a single quantum particle, Phys. Rev. Lett. 120, 060503 (2018). 
[MMD+18] F. Massa, A. Moqanaki, F. Del Santo, B. Dakić, and P. Walther, Experimental two-way communication with one photon, arXiv:1802.05102 (2018).