Variational Quantum Eigensolver (VQE) algorithms have generally involved the optimization of a series of parameterized quantum gates designed to approximate the quantum state of a molecule.  While this has many attractive features such as robustness to noise, the limited coherence times and frequent gate errors limit the number of these gates in near-term quantum devices. Our team has recently proposed a  variational pulse-shaping algorithm known as ctrl-VQE to address these issues by eliminating the need for parameterized quantum circuits. Through numerical simulations, we have observed reductions in the coherence time required of multiple orders of magnitude. In this talk, we will look at the shortest possible pulses for ctrl-VQE to prepare target molecular wavefunctions for a given device Hamiltonian describing coupled transmon qubits. We find that the time-optimal pulses that do this have a bang-bang form consistent with Pontryagin’s maximum principle. We further investigate how the minimal state preparation time is impacted by truncating the transmons to two versus more levels. We find that leakage outside the computational subspace (something that is usually considered problematic) speeds up the state preparation, further reducing device coherence time demands.

Minimizing state preparation times in pulse-level variational molecular simulation

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

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