Elizabeth Crosson¹, Tameem Albash^1,2, Itay Hen^3,4, and A. P. Young⁵

Quantum 4, 334 (2020) https://doi.org/10.22331/q-2020-09-24-334

Quantum fluctuations driven by non-stoquastic Hamiltonians have been conjectured to be an important and perhaps essential missing ingredient for achieving a quantum advantage with adiabatic optimization. We introduce a transformation that maps every non-stoquastic adiabatic path ending in a classical Hamiltonian to a corresponding stoquastic adiabatic path by appropriately adjusting the phase of each matrix entry in the computational basis. We compare the spectral gaps of these adiabatic paths and find both theoretically and numerically that the paths based on non-stoquastic Hamiltonians have generically smaller spectral gaps between the ground and first excited states, suggesting they are less useful than stoquastic Hamiltonians for quantum adiabatic optimization. These results apply to any adiabatic algorithm which interpolates to a final Hamiltonian that is diagonal in the computational basis.

¹Center for Quantum Information and Control (CQuIC), Department of Physics and Astronomy , University of New Mexico, Albuquerque, NM 87131, USA
²Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM 87131, USA
³Information Sciences Institute, University of Southern California, Marina del Rey, California 90292, USA
⁴Department of Physics and Astronomy and Center for Quantum Information Science & Technology, University of Southern California, Los Angeles, California 90089, USA
⁵Department of Physics, University of California, Santa Cruz, California 95064, USA