Abstract
The quantum alternating operator ansatz (QAOA) is a prominent example of variational quantum algorithms. We propose a generalized QAOA called CD-QAOA, which is inspired by the counterdiabatic driving procedure, designed for quantum many-body systems and optimized using a reinforcement learning (RL) approach. The resulting hybrid control algorithm proves versatile in preparing the ground state of quantum-chaotic many-body spin chains by minimizing the energy. We show that using terms occurring in the adiabatic gauge potential as generators of additional control unitaries, it is possible to achieve fast high-fidelity many-body control away from the adiabatic regime. While each unitary retains the conventional QAOA-intrinsic continuous control degree of freedom such as the time duration, we consider the order of the multiple available unitaries appearing in the control sequence as an additional discrete optimization problem. Endowing the policy gradient algorithm with an autoregressive deep learning architecture to capture causality, we train the RL agent to construct optimal sequences of unitaries. The algorithm has no access to the quantum state, and we find that the protocol learned on small systems may generalize to larger systems. By scanning a range of protocol durations, we present numerical evidence for a finite quantum speed limit in the nonintegrable mixed-field spin- Ising and Lipkin-Meshkov-Glick models, and for the suitability to prepare ground states of the spin-1 Heisenberg chain in the long-range and topologically ordered parameter regimes. This work paves the way to incorporate recent success from deep learning for the purpose of quantum many-body control.
- Received 24 November 2020
- Revised 28 May 2021
- Accepted 15 July 2021
DOI:https://doi.org/10.1103/PhysRevX.11.031070
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.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Strongly correlated quantum many-body systems describe condensed-matter materials which, once understood, are expected to lead to new technologies based on quantum mechanics. It has recently been realized that ground-state properties that give rise to exotic quantum phenomena (such as superconductivity or topological states of matter) can be simulated on highly controllable AMO-based quantum simulators. A major obstacle to accessing this exciting new physics is the preparation of many-body ground states on the quantum simulator. Our work presents a new physics-inspired, machine-learning-based approach to fast and efficient many-body quantum control.
We develop a generalization of the quantum alternating operator ansatz—a well-established quantum control algorithm—specifically tailored to prepare quantum many-body states. To do this, we integrate counterdiabatic driving—a concept from quantum dynamics for transitionless driving—into a physics-informed ansatz. This allows us to construct a suitable control protocol space, designed for the specific many-body system of interest.
To find the optimal protocol in this large control space, we apply a novel reinforcement learning algorithm based on deep autoregressive neural networks. The resulting hybrid variational algorithm combines the best of the quantum alternating operator ansatz and counterdiabatic driving to enable the preparation of high-fidelity quantum many-body ground states in systems lacking closed-form analytical solutions.
Our study opens the door to identifying relevant control degrees of freedom in quantum many-body systems. The generalized quantum alternating operator ansatz that we develop is suitable for both digital and analog quantum simulators. In addition, this work displays a beneficial symbiosis between reinforcement learning and optimal quantum control.
