Large-Sized VQE Performance Profiling in Quantum Chemistry Using a Multi-Node Quantum Simulator

Quantum simulators have been actively developed that faithfully simulate the quantum computer operations on a classical computer. Since the amount of memory and operations required by quantum simulators increases exponentially with the number of qubits, MPI (Message Passing Interface) and distributed processing, which are methods to effectively use a large number of computing resources, can be used to achieve higher computation speed. In this paper, we profile the performance of the variational quantum eigensolver (VQE) algorithm by applying it to a multi-node quantum simulator to calculate the energy values of carbon dioxide (C<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O2</inf>) molecule. We also discuss how the size of CI (configuration interaction) ansatz and the convergence threshold of the classical optimization change the energy values. Experimental results demonstrate that the computational time is reduced as the number of computation nodes increases. The speed-up ratio is increased as the number of qubits increases. When the qubit size is 30, a maximum of 12.2 times speed-up is achieved if the computing node size is increased from 1 to 128.