Quantum information theory predicts that communication technology can be enhanced by using quantum signals to transfer classical bits. In order to fulfill this promise, the message-carrying signals must interact coherently at the decoding stage via a joint-detection receiver (JDR), whose realization with optical technologies remains an outstanding open problem to date. We introduce a supervised-learning framework for the systematic discovery of new JDR designs based on parametrized photonic integrated circuits. Our framework relies on the synthesis of a training set comprising quantum codewords and the corresponding classical message label; the codewords are processed by the JDR circuit and, after photo-detection, produce a guess for the label. The circuit parameters are then updated by minimizing a suitable loss function, reaching an optimal JDR design for that specific architecture. We showcase our method with coherent-state codes for the pure-loss bosonic channel, modelling optical-fiber and space communication, with a circuit architecture comprising linear optics, squeezing and threshold photo-detectors. We train JDR circuits for several code families, varying energy and code-size. We discover optical JDR circuit setups for maximum-size codes and small message-length that offer up to a
3-fold enhancement in the bit decoding rate with respect to the optimal single-symbol receiver, and less than
7%-away from the theoretically optimal decoder, for which an explicit design is missing to date. Furthermore, the discovered receivers surpass previous JDR designs both in terms of bit decoding and bit transmission rate. Finally, we observe that the best-performing codes are those which can be mapped, via the JDR's optical processing, to modulations with different energy levels on different symbols, making the message symbols more distinguishabile via photo-detection.
This study proposes a new coding function for the symmetric W state.Based on the new coding function,a theoretical protocol of deterministic quantum communication(DQC) is proposed.The sender can use the proposed coding function to encode his/her message,and the receiver can perform the imperfect Bell measurement to obtain the sender's message.In comparison to the existing DQC protocols that also use the W class state,the proposed protocol is more efcient and also more practical within today's technology.Moreover,the security of this protocol is analyzed to show that any eavesdropper will be detected with a very high probability under both the ideal and the noisy quantum channel.
Abstract In the 40 years since the BB84 protocol was proposed, the practical progress of quantum communication has been relatively slow, because many key technologies have not yet made breakthroughs. This paper proposes a model that can be supported by existing technologies, that is, three-non quantum communication which has no quantum key distribution, no teleportation, and no information transmission. Its working principle is that Alice uses fiber channel or free space to send polarized entangled photon streams to Bob and has the controllable decoherence of entangled photons with the industrial-grade optoelectronic devices, and her control role is equivalent to information coding to realize communication functions. It also has other characteristics such as no requirement for code rate, single-photon detection, quantum base operations and classical channel, etc. It has a low requirement for light sources and transmission channels and is easy to implement.