Breakdown of the weak coupling limit in quantum annealing
- URL: http://arxiv.org/abs/2111.07560v2
- Date: Tue, 10 May 2022 08:20:27 GMT
- Title: Breakdown of the weak coupling limit in quantum annealing
- Authors: Yuki Bando, Ka-Wa Yip, Huo Chen, Daniel A. Lidar and Hidetoshi
Nishimori
- Abstract summary: We report on experiments using the D-Wave 2000Q device.
We concentrate on the total and partial success probabilities, the latter being the probabilities of finding each of two degenerate ground states of all spins up or all spins down.
Our results present a challenge to the sufficiency of the weak system-bath coupling limit in describing the dynamics of current experimental quantum annealers.
- Score: 0.0
- License: http://creativecommons.org/licenses/by/4.0/
- Abstract: Reverse annealing is a variant of quantum annealing, in which the system is
prepared in a classical state, reverse-annealed to an inversion point, and then
forward-annealed. We report on reverse annealing experiments using the D-Wave
2000Q device, with a focus on the $p=2$ $p$-spin problem, which undergoes a
second order quantum phase transition with a gap that closes polynomially in
the number of spins. We concentrate on the total and partial success
probabilities, the latter being the probabilities of finding each of two
degenerate ground states of all spins up or all spins down, the former being
their sum. The empirical partial success probabilities exhibit a strong
asymmetry between the two degenerate ground states, depending on the initial
state of the reverse anneal. To explain these results, we perform open-system
simulations using master equations in the limits of weak and strong coupling to
the bath. The former, known as the adiabatic master equation (AME), with
decoherence in the instantaneous energy eigenbasis, predicts perfect symmetry
between the two degenerate ground states, thus failing to agree with the
experiment. In contrast, the latter, known as the polaron transformed Redfield
equation (PTRE), is in close agreement with experiment. Thus our results
present a challenge to the sufficiency of the weak system-bath coupling limit
in describing the dynamics of current experimental quantum annealers, at least
for reverse annealing on timescales of a microsecond or longer.
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