Distributed Quantum Computation

Introduction

Near-term quantum computers can hold only a small number of qubits. One way to facilitate large-scale quantum computations is through a distributed network of quantum computers. In this work, we consider the problem of distributing quantum programs represented as quantum circuits across a quantum network of heterogeneous quantum computers, in a way that minimizes the overall communication cost required to execute the distributed circuit. 

We consider two ways of communicating: cat-entanglement that creates linked copies of qubits across pairs of computers, and teleportation. The heterogeneous computers impose constraints on cat-entanglement and teleportation operations that can be chosen by an algorithm. We first focus on a special case that only allows cat-entanglements and not teleportations for communication. We provide a twostep heuristic for solving this specialized setting: (i) finding an assignment of qubits to computers using Tabu search, and (ii) using an iterative greedy algorithm designed for a constrained version of the set cover problem to determine cat-entanglement operations required to execute gates locally. 

For the general case, which allows both forms of communication, we propose two algorithms that subdivide the quantum circuit into several portions and apply the heuristic for the specialized setting on each portion. Teleportations are then used to stitch together the solutions for each portion. 

Published Papers

1. Sundaram, Ranjani G., Himanshu Gupta, and C. R. Ramakrishnan. "Distributed Quantum Computation with Minimum Circuit Execution Time over Quantum Networks." arXiv preprint arXiv:2405.07499 (2024). 

2. Sundaram, Ranjani G., and Himanshu Gupta. "Distributing quantum circuits using teleportations." In 2023 IEEE International Conference on Quantum Software (QSW), pp. 186-192. IEEE, 2023. 

3. Sundaram, Ranjani G., Himanshu Gupta, and C. R. Ramakrishnan. "Distribution of quantum circuits over general quantum networks." In 2022 IEEE International Conference on Quantum Computing and Engineering (QCE), pp. 415-425. IEEE, 2022. 

4. G Sundaram, Ranjani, Himanshu Gupta, and C. R. Ramakrishnan. "Efficient distribution of quantum circuits." In 35th International Symposium on Distributed Computing (DISC 2021). Schloss Dagstuhl-Leibniz-Zentrum für Informatik, 2021.