A Compiler Framework for Enabling Collective Communication in Distributed Quantum Programs

Distributed quantum computing (DQC) is a promising approach to extending the computational power of near-term quantum devices. However, the non-local quantum communication between quantum devices is much more expensive and error-prone than the local quantum communication within each quantum device. Previous work on the DQC communication optimization focus on optimizing the communication protocol for each individual non-local gate and then adopt quantum compilation designs which are designed for local multi-qubit gates in a single quantum computer. The communication patterns in distributed quantum programs are not yet well studied, leading to a far-from-optimal communication cost. In this talk, we will introduce our recent work on compiler support for distributed quantum computers. First, we identify burst communication, a specific qubit-node communication pattern that widely exists in many distributed programs and can be leveraged to guide communication overhead optimization. To this end, we propose AutoComm, an automatic compiler framework to first extract the burst communication patterns from the input programs, and then optimize the communication steps of burst communication discovered. Experimental results show that AutoComm can reduce the communication resource consumption and the program latency by 75.6% and 71.4% on average, respectively. Second, we discover that the efficiency of quantum communication, especially collective communication, can be significantly boosted by decoupling communication resources from remote operations, that is, the communication hardware would be used only for preparing remote entanglement, and the computational hardware, the component used to store program information, would be used for conducting remote gates. We develop a compiler framework to optimize the collective communication happening in distributed quantum programs. We decouple the communication preparation process in communication hardware from the remote gates conducted in computational hardware by buffering EPR pairs generated by communication hardware in qubits of the computational hardware. Experimental results show that the proposed framework can halve the communication cost of various distributed quantum programs.