Locally Suppressed Transverse-Field Protocol for Diabatic Quantum Annealing

TL;DR

The paper introduces the LSTF protocol, a heuristic method that enables diabatic quantum annealing on stoquastic problems by manipulating local fields to create energy gap double minima, facilitating quantum speed-ups and experimental testing.

Contribution

It proposes the LSTF protocol to make stoquastic problems compatible with DQA, enabling new experiments and potential speed-ups in quantum annealing.

Findings

LSTF creates double minima in energy gaps for diabatic transitions.

LSTF allows DQA experiments on existing hardware with independent control.

Relaxation rate depends only on the target qubit, aiding decoherence analysis.

Abstract

Diabatic quantum annealing (DQA) is an alternative algorithm to adiabatic quantum annealing (AQA) that can be used to circumvent the exponential slowdown caused by small minima in the annealing energy spectrum. We present the locally suppressed transverse-field (LSTF) protocol, a heuristic method for making stoquastic optimization problems compatible with DQA. We show that, provided an optimization problem intrinsically has magnetic frustration due to inhomogeneous local fields, a target qubit in the problem can always be manipulated to create a double minimum in the energy gap between the ground and first excited states during the evolution of the algorithm. Such a double energy minimum can be exploited to induce diabatic transitions to the first excited state and back to the ground state. In addition to its relevance to classical and quantum algorithmic speed-ups, the LSTF protocol enables DQA proof-of-principle and physics experiments to be performed on existing hardware, provided independent controls exist for the transverse qubit magnetization fields. We discuss the implications on the coherence requirements of the quantum annealing hardware when using the LSTF protocol, considering specifically the cases of relaxation and dephasing. We show that the relaxation rate of a large system can be made to depend only on the target qubit presenting new opportunities for the characterization of the decohering environment in a quantum annealing processor.