Unitary coupled cluster is one of the most commonly used ansatzes for quantum chemistry simulations on quantum computers using variational quantum eigensolver method. Although it is a chemistry inspired ansatz, which explores chemically relevant part of the Hilbert space, in many cases it still contains many fermionic operators that don’t contribute to correlation energy of a given molecule. We show that molecular symmetries can be used to pre-screen the excitation operators in the ansatz that have zero amplitudes due to symmetry. As a result, the depth of the quantum circuit to implement this ansatz can be reduced by 80-90% for highly symmetric molecules. Additionally, we propose a unitary selective coupled cluster method, which can iteratively construct a unitary coupled cluster ansatz with excitation operators of arbitrary order. We demonstrate its performance on a set of small molecules and discuss the prospects of the method and potential ways to improve it.

Unitary selective coupled cluster method

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.