Linear-Scaling Quantum Circuits for Computational Chemistry

Abstract: We have recently constructed compact, CNOT-efficient, quantum circuits for fermionic and qubit excitations of arbitrary many-body rank [I. Magoulas and F.A. Evangelista, J. Chem. Theory Comput. 19, 822 (2023)]. Here, we present approximations to these circuits that substantially reduce the CNOT counts even further. Our preliminary numerical data, using the selected projective quantum eigensolver approach, demonstrate that there is practically no loss of accuracy in the energies compared to the parent implementation while the ensuing symmetry breaking is essentially negligible.