QLunch: Oskar Leimkuhler

Speaker: Oskar Leimkuhler

Title: Barriers to dequantization of near-term molecular electronic structure methods

Abstract: In this talk I discuss my recent work as part of my PhD with Birgitta Whaley [arXiv:2503.21041, to appear in PRX Quantum]. I will cover the main results of the paper, which establish universality under post-selection and worst-case simulation hardness of particle number conserving matchgate circuits supplemented with fermionic magic state inputs, as well as universality and BQP-completeness when supplemented with two-body fermionic excitation gates. I will then discuss the application of these results to non-orthogonal quantum eigensolvers for molecular electronic structure calculations, some average-case hardness conjectures, and some broader implications for the computational hardness of quantum chemistry.