Efficient state preparation for the Schwinger model with a theta term

Journal Article · Thu Apr 24 04:00:00 EDT 2025 · Physical Review. D.

DOI:https://doi.org/10.1103/PhysRevD.111.074515· OSTI ID:2562697

Bazavov, Alexei; Henke, Brandon; Hostetler, Leon; Lee, Dean; Lin, Huey-Wen; Pederiva, Giovanni; Shindler, Andrea

We present a comparison of different quantum state preparation algorithms and their overall efficiency for the Schwinger model with a theta term. While adiabatic state preparation is proved to be effective, in practice it leads to large gate counts to prepare the ground state. The quantum approximate optimization algorithm (QAOA) provides excellent results while keeping the counts small by design, at the cost of an expensive classical minimization process. We introduce a “blocked” modification of the Schwinger Hamiltonian to be used in the QAOA that further decreases the length of the algorithms as the size of the problem is increased. The rodeo algorithm (RA) provides a powerful tool to efficiently prepare any eigenstate of the Hamiltonian, as long as its overlap with the initial guess is large enough. We obtain the best results when combining the blocked QAOA ansatz and the RA, as this provides an excellent initial state with a relatively short algorithm without the need to perform any classical steps for large problem sizes.

Published by the American Physical Society 2025

• Sponsoring Organization: USDOE
• Grant/Contract Number: SC0021152; SC0023658; SC0019139; SC0023663
• OSTI ID: 2562697
• Alternate ID(s): OSTI ID: 2571985
• Journal Information: Physical Review. D., Journal Name: Physical Review. D. Journal Issue: 7 Vol. 111; ISSN PRVDAQ; ISSN 2470-0010
• Publisher: American Physical Society
• Country of Publication: United States
• Language: English