FPGA-based Deterministic and Low-Latency Control for Distributed Quantum Computing.

Distributed quantum computing is a promising solution for creating large-scale quantum computers. In such scenarios, quantum processing units (QPUs) are connected to each other via quantum and classical links. To increase the performance in such a distributed manner, and due to the fragile nature of quantum bits and their decoherence with time, the impact of classical links such as communication latency and jitter between QPUs shall be considered. Here, we propose a low-latency and time-deterministic FPGA-based network supporting execution of distributed quantum circuits. We focus on transmissions of measurement result and control messages as well as synchronization in a distributed network. We demonstrate that a message is transmitted with 361.60 ns between QPUs using optical Ethernet. Synchronization reaches 9.6 ns precision using only Ethernet frames and can reach 21 ps with an external clock. Further, a use-case example of an Inverse Quantum Fourier Transform is implemented to evaluate the impact in terms of latency for inter-QPU data transfers. Our theoretical error analysis and simulation results show that the latency added by our FPGA-controlled network has a negligible impact on the quantum algorithm performance for practical values of memory decoherence time.