QuComm: Optimizing Collective Communication for Distributed Quantum Computing

Distributed quantum computing (DQC) is a scalable way to build a large-scale quantum computing system. Previous compilers for DQC focus on either qubit-to-qubit inter-node gates or qubit-to-node nonlocal circuit blocks, missing opportunities of optimizing collective communication which consists of nonlocal gates over multiple nodes. In this paper, we observe that by utilizing patterns of collective communication, we can greatly reduce the amount of inter-node communication required to implement a group of nonlocal gates. We propose QuComm, the first compiler framework which unveils and analyzes collective communication patterns hidden in distributed quantum programs and efficiently routes inter-node gates on any DQC architecture based on discovered patterns, cutting down the overall communication cost of the target program. We also provide the first formalization of the communication buffer concept in DQC compiling. The communication buffer utilizes data qubits to store remote entanglement so that we can ensure enough communication resources on any DQC architecture to support the proposed optimizations for collective communication. Experimental results show that, compared to the state-of-the-art baseline, QuComm reduces the amount of inter-node communication by 54.9% on average, over various distributed quantum programs and DQC hardware configurations.