Quantum Optics Seminar: Benjamin Schiffer, Max Planck Institute of Quantum Optics

Navigating small gaps in the quantum adiabatic algorithm

Preparing ground states on quantum devices is a problem of great significance in physics, with deep implications in the field of combinatorial optimization. The adiabatic algorithm is known to return the ground state for sufficiently long preparation times, which depend on the a priori unknown spectral gap. In this talk, I first present a variational quantum adiabatic algorithm for optimized adiabatic paths.  We seek to combine the strengths of the adiabatic and the variational approaches for fast and high-fidelity ground state preparation while keeping the number of measurements as low as possible [1].

Second, I introduce Rydberg atom arrays as an experimental platform for solving optimization problems. We construct graph instances for which the minimum gap decays superexponentially with system size, implying a superexponentially large time to solution via adiabatic evolution. We investigate remedies and show that quenches in these models exhibit signatures of quantum many-body scars, which in turn, can circumvent the small gaps [2]. Finally, I share recent results using QuEra's programmable quantum simulator. We experimentally realize a sweep-quench-sweep quantum algorithm that can provide a shortcut to adiabaticity for a certain class of problems where adiabatic algorithms fail.

[1] Schiffer, B., Tura, J., & Cirac, J. I. (2022). Adiabatic spectroscopy and a variational quantum adiabatic algorithm. PRX Quantum, 3(2), 020347.

[2] Schiffer, B., Wild, D. S., Maskara, N., Cain, M., Lukin, M. D., & Samajdar, R. (2024). Circumventing superexponential runtimes for hard instances of quantum adiabatic optimization. Physical Review Research, 6(1), 013271.