A new gold standard: using perturbation theory to improve upon the unitary coupled cluster ansatz

In this talk, I will discuss recent developments that alleviate some of the drawbacks that plague quantum simulations of chemistry in current quantum computers. The unitary coupled cluster ansatz (UCC) is ubiquitous in studies involving the variational quantum eigensolver (VQE), the quintessential algorithm in molecular simulations. However, the low-rank approximation to the ground state that the UCC ansatz affords in near-term quantum computers is not always accurate. However, this accuracy can be significantly improved by invoking perturbation theory arguments like those that elevated CCSD(T) to be referred to as the "gold standard" of quantum chemistry. I show how many-body perturbation theory (MBPT) can lead to better energetics in a variety of small molecules, with no further burden to the quantum computer.