Quantum Key Distribution Systems, Digital Control Module Design

Quantum information is a new subject that develops upon the combination of quantum physics and information science. Since the introduction of quantum mechanics, it has the incomparable advantages and prospects to classic information, and has aroused wide interest. At present, great progress has been made in both theory and experiment. Further more, pratical commercial products have come into being.Quantum information includes two areas: quantum communication and quantum computing. Quantum computers and quantum algorithm for quantum computers are the subjects that quantum computing studies. And for quantum communication, the major research subjects lie in quantum cryptography, quantum teleportion, and long-distance quantum communication technology. Quantum cryptography, also known as quantum key distribution (QKD), uses quantum mechanical properties to ensure communication security. It enables the product and sharing of a random, secure key to encrypt and decrypt information between the two parties in communication.In this article, we focus on the field of quantum communication.Since the first quantum key distribution protocol proposed by Bennett and Brassard in 1984, many QKD experiments based on different protocols have been completed using different quantum informatin channels. Decades, governments, research institutions and companies invest a lot of resources to the study of quantum secure communication, making it come to our everyday life from labs. Quantum Physics and Quantum Information Laboratory in USTC develops a kind of QKD system, which is an attempt of practicality.In the work of this article, circuit design of digital control module in QKD system has completed, including FPGA-based control board and synchronization-acquisition-delay board. While having a good cost control, the board achieves a variety of complex logic by using FPGA as the core, which is powerful and flexible. The control board uses USB to communicate with PC and communicates with other electronics modules through a custom backplane bus, completing controlling function of the electronics section. Synchronization-acquisition-delay board receives and discriminates the sync light pulses, provides them to single photon detectors as gate signals after adjustable delay. Discriminating circuit on board can capture sync signal at the voltage level of 30mV, and delay the sync signal at 100ps per step. The delay range is 200ns, and the jitter between light and sync signal after delay is at 300ps.With the circuit design of digital control module, the FPGA logic design of control board has completed. FPGA logic, including the transmitter logic, the receiver logic and USB interface logic, is integrated in the same project. You can use the mode selection command to select the appropriate part of the work. In the field of transmitter, the main function of the logic is to receive and analyze the host PC command, generate sync signal, control laser and analog voltage board,encode and upload data.In the receiver's field, the logic completes receiving of host PC command, acquisition of detector data, data encoding and uploading.The digital control module designed and developed in this paper achieves the overall system design requirements.It operates normally, and has reached production and industrialization requirements. Recently in Hefei, based on existing commercial fiber and the quantum key distribution system developed, the research team has built the first all-pass type quantum communication networks in the world. It achieved a full functional operation, and brought over to the direction of industrialization.