Adiabatic reverse annealing is robust to low-temperature decoherence

TL;DR

This paper demonstrates that adiabatic reverse annealing remains effective in open quantum systems at low temperatures, with environmental effects sometimes even aiding the process, contrary to previous concerns about decoherence.

Contribution

The study provides an analytical understanding of ARA's robustness to decoherence, showing it can succeed at low temperatures and that environmental effects can sometimes be beneficial.

Findings

ARA can follow equilibrium states without phase transitions at low temperature.

High temperature can cause ARA to fail due to disorder or lack of transition paths.

Environment can sometimes facilitate ARA by creating transition-avoiding paths.

Abstract

Adiabatic reverse annealing (ARA) is an improvement to conventional quantum annealing (QA) that uses an initial guess at the desired ground state to circumvent problematic phase transitions. Despite encouraging results in the closed-system setting, Ref. [1] has suggested on the basis of numerical simulations that ARA may lose its advantage in the presence of decoherence. Here, we revisit this problem from a more analytical perspective. Using the $p$-spin model as a solvable example, together with the adiabatic master equation to describe the effects of the environment (valid at weak coupling), we show that ARA can in fact succeed in open systems but that the temperature of the environment plays a key role. We first demonstrate that, in the adiabatic limit, the system will follow the instantaneous equilibrium state as long as the protocol does not pass through any (finite-temperature) phase transitions. Given this, there are two distinct mechanisms by which ARA can break down at high temperature: either there are no paths that avoid transitions, or the equilibrium state itself is disordered. When the temperature is sufficiently low that neither of these occur, then ARA succeeds. Remarkably, there are even situations in which the environment benefits ARA: we find parameter values for which no transition-avoiding paths exist at zero temperature but such paths appear at non-zero temperature.