Frequency-Division Multiplexing Continuous Variable Quantum Dense Coding with Broadband Entanglement

Abstract

Quantum dense coding (QDC) provides great potential for high-capacity quantum communication. However, it is highly demanded for practical applications to realize high-capacity QDC with multiple coded information. Here, a high-capacity QDC with multiple streams is reported in different channels simultaneously through frequency-division multiplexing (FDM). The broadband entangled state is generated from a pair of degenerate optic al parametric amplifiers with short cavity lengths. Based on the resultant broadband entanglement, multiple pieces of information coded using binary phase shift keying (BPSK) are transferred with the FDM method. As an experimental demonstration, four pieces of information composed of pseudo-random numbers are transmitted at a rate of 4 Mbit s^–1 using BPSK encoding. The decoded bit error rate reaches ${10}^{-3}$, which is an average 35-fold improvement compared with the classical scheme. Furthermore, it is possible to make full use of sideband resource for four different information by using orthogonal FDM. This scheme can be extended to more different information by directly increasing the FDM sideband subchannels, and opens an avenue to construct high-capacity quantum communication, while minimizing the cost of quantum resource.