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  • Open Access

Continuous-time quantum control across an exponentially small bottleneck in a frustrated Ising ring model

Vincenzo Roberto Arezzo1,*, Kiran Thengil1, and Giuseppe E. Santoro1,2

  • *Contact author: varezzo@sissa.it
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Phys. Rev. A 114, 042438 – Published 19 October, 2026

DOI: https://doi.org/10.1103/wwqn-c9cb

Abstract

Continuous-time quantum annealing (QA) is a strategy for preparing the ground state of nontrivial many-body systems. In its standard form, the dynamics is generated by a time-dependent interpolation between a simple driving Hamiltonian and the target problem Hamiltonian, usually implemented through a linear schedule. This approach faces the crucial bottleneck of small spectral gaps, which may require exponentially long annealing times to ensure adiabaticity. Here, we show how to implement quantum control over the annealing schedule in a frustrated Ising ring, one of the simplest models exhibiting an exponentially small bottleneck gap. By optimizing smooth continuous-time annealing schedules with a dressed chopped random basis (CRAB) approach, and using a digitized representation of the dynamics to efficiently evaluate gradients, we construct protocols that strongly outperform standard fixed schedules. The optimized dynamics bypasses the bottleneck through a strongly nonadiabatic mechanism, leading to efficient ground-state preparation despite the exponentially small minimum gap. In particular, the annealing time required to reach a fixed residual-energy threshold is found to grow linearly with system size rather than exponentially. We further examine a lowest-order variational counterdiabatic correction and find that, once schedule optimization is allowed, it does not lead to any improvement.

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Phys. Rev. A 114, 042438– Published 19 October, 2026
  • Received 10 June 2026
  • Accepted 30 September 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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