Resonator reset in circuit QED by optimal control for large open quantum systems

TL;DR

This paper introduces an optimized open GRAPE algorithm for large open quantum systems, significantly speeding up quantum control tasks like resonator reset in circuit QED by avoiding matrix exponential calculations.

Contribution

The paper presents a novel implementation of open GRAPE that reduces computational complexity and memory usage, enabling faster quantum control optimization in large open quantum systems.

Findings

Achieved over four times faster resonator reset compared to passive methods

Demonstrated polynomial speed-up over standard open GRAPE implementations

Reduced memory requirements for large-scale quantum control problems

Abstract

We study an implementation of the open GRAPE (Gradient Ascent Pulse Engineering) algorithm well suited for large open quantum systems. While typical implementations of optimal control algorithms for open quantum systems rely on explicit matrix exponential calculations, our implementation avoids these operations leading to a polynomial speed-up of the open GRAPE algorithm in cases of interest. This speed-up, as well as the reduced memory requirements of our implementation, are illustrated by comparison to a standard implementation of open GRAPE. As a practical example, we apply this open-system optimization method to active reset of a readout resonator in circuit QED. In this problem, the shape of a microwave pulse is optimized such as to empty the cavity from measurement photons as fast as possible. Using our open GRAPE implementation, we obtain pulse shapes leading to a reset time over four times faster than passive reset.