Feedback-Driven Ground-State Search in Coupled Laser Arrays

TL;DR

This paper introduces a feedback-driven annealing method in semiconductor laser arrays that enhances the ability to find ground states in complex energy landscapes, offering a scalable approach for solving hard optimization problems.

Contribution

It demonstrates a novel intrinsic feedback mechanism in laser arrays that enables effective escape from local minima during ground-state searches, with tunable timescales controlling defect suppression.

Findings

Nearly 100% ground-state probability achieved in experiments.

Defect suppression governed by the ratio of amplitude stabilization and phase locking timescales.

Identical timescale ratios lead to similar defect probabilities, independent of specific parameters.

Abstract

Optimisation problems, which appear in numerous fields of science and industry, are challenging to solve even with modern supercomputers. Many such problems can be mapped onto ground-state searches of spin Hamiltonians, implemented on various physical platforms whose intrinsic dynamics are analogous to spin systems. However, the complex energy landscape of spin Hamiltonians often traps the system in local minima, preventing the system from reaching the ground-state (global minimum). We demonstrate an intrinsic feedback-driven annealing mechanism in class-B semiconductor laser arrays arising from the interplay of internal ($\alpha$) and external ($\eta$) coupling. The instantaneous phase configuration self-modulates amplitude fluctuations, which act as an effective temperature, dynamically reshaping the potential and enabling the system to escape from local minima. Using a one-dimensional ring laser array, we analyze defect formation in the $\alpha$-$\eta$ parameter space and identify an optimal regime achieving nearly 100% ground-state probability. Although both $\alpha$ and $\eta$ are essential for the feedback loop, defect suppression results from modifying two competing timescales: amplitude stabilization (t_amp) and phase locking (t_phase), analogous to the Kibble-Zurek mechanism. These timescales can be tuned independently via $\alpha$ or $\eta$. Identical timescale ratios yield identical defect probabilities, confirming that relative timescales, not specific parameters, govern defect formation. Our findings establish internal feedback-driven annealing as a practical route to ground-state search in semiconductor laser arrays, providing a foundation for efficient and scalable laser-based spin simulators for tackling hard optimization problems.