Gate-free state preparation for fast variational quantum eigensolver simulations

Journal Article · 26 October 2021 · npj Quantum Information

DOI: https://doi.org/10.1038/s41534-021-00493-0 · OSTI ID:1827749

Meitei, Oinam Romesh ; Gard, Bryan T. ; Barron, George S. ; Pappas, David P.; Economou, Sophia E. ; Barnes, Edwin; Mayhall, Nicholas J.

Abstract The variational quantum eigensolver is currently the flagship algorithm for solving electronic structure problems on near-term quantum computers. The algorithm involves implementing a sequence of parameterized gates on quantum hardware to generate a target quantum state, and then measuring the molecular energy. Due to finite coherence times and gate errors, the number of gates that can be implemented remains limited. In this work, we propose an alternative algorithm where device-level pulse shapes are variationally optimized for the state preparation rather than using an abstract-level quantum circuit. In doing so, the coherence time required for the state preparation is drastically reduced. We numerically demonstrate this by directly optimizing pulse shapes which accurately model the dissociation of H ₂ and HeH ⁺ , and we compute the ground state energy for LiH with four transmons where we see reductions in state preparation times of roughly three orders of magnitude compared to gate-based strategies.

• Research Organization: Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, VA (United States)
• Sponsoring Organization: USDOE; USDOE Office of Science (SC)
• Grant/Contract Number: SC0018326; SC0019199; SC0019318
• OSTI ID: 1827749
• Journal Information: npj Quantum Information, Journal Name: npj Quantum Information Journal Issue: 1 Vol. 7; ISSN 2056-6387
• Publisher: Nature Publishing GroupCopyright Statement
• Country of Publication: United Kingdom
• Language: English