From Pulses to Circuits and Back Again: A Quantum Optimal Control Perspective on Variational Quantum Algorithms

The last decade has witnessed remarkable progress in the development of quantum technologies. Although fault-tolerant devices likely remain years away, the noisy intermediate-scale quantum devices of today may be leveraged for other purposes. Leading candidates are variational quantum algorithms (VQAs), which have been developed for applications including chemistry, optimization, and machine learning, but whose implementations on quantum devices have yet to demonstrate improvements over classical capabilities. In this Perspective, we propose a variety of ways that the performance of VQAs could be informed by quantum optimal control theory. A major theme throughout is the need for sufficient control resources in VQA implementations; we discuss different ways this need can manifest, outline a variety of open questions, and look to the future.

Automated summary

The development of quantum technologies has made significant progress over the past decade. While fault-tolerant devices are still years away, current noisy intermediate-scale quantum devices can be used for other purposes. Variational quantum algorithms (VQAs) are a leading candidate, but their implementations on quantum devices have yet to show improvements over classical capabilities. This Perspective discusses various ways in which the performance of VQAs could be enhanced by quantum optimal control theory, highlighting the importance of sufficient control resources in VQA implementations and addressing open questions for the future.