Bandwidth-Limited Control and Ringdown Suppression in High-Q Resonators

TL;DR

This paper introduces an optimal control theory-based pulse design that integrates ringdown suppression to improve quantum operations in high-Q resonators, reducing deadtime and enhancing measurement sensitivity.

Contribution

The authors develop a numerical pulse optimization method that includes ringdown suppression, significantly improving quantum control and measurement in high-Q resonator systems.

Findings

Reduced spectrometer deadtime with optimized pulses

Enhanced signal-to-noise ratio in measurements

Successful experimental demonstration on spin systems

Abstract

We describe how the transient behavior of a tuned and matched resonator circuit and a ringdown suppression pulse may be integrated into an optimal control theory (OCT) pulse-design algorithm to derive control sequences with limited ringdown that perform a desired quantum operation in the presence of resonator distortions of the ideal waveform. Inclusion of ringdown suppression in numerical pulse optimizations significantly reduces spectrometer deadtime when using high quality factor (high-Q) resonators, leading to increased signal-to-noise ratio (SNR) and sensitivity of inductive measurements. To demonstrate the method, we experimentally measure the free-induction decay of an inhomogeneously broadened solid-state free radical spin system at high Q. The measurement is enabled by using a numerically optimized bandwidth-limited OCT pulse, including ringdown suppression, robust to variations in static and microwave field strengths. We also discuss the applications of pulse design in high-Q resonators to universal control of anisotropic-hyperfine coupled electron-nuclear spin systems via electron-only modulation even when the bandwidth of the resonator is significantly smaller than the hyperfine coupling strength. These results demonstrate how limitations imposed by linear response theory may be vastly exceeded when using a sufficiently accurate system model to optimize pulses of high complexity.