Amplitude and frequency sensing of microwave fields with a superconducting transmon qudit

TL;DR

This paper introduces a method to accurately measure the amplitude and frequency of microwave signals on superconducting circuits using a transmon qudit, enhancing calibration and control in quantum computing.

Contribution

It demonstrates a novel on-chip sensing technique utilizing ac Stark shifts of transmon levels to infer microwave field properties over a broad frequency range.

Findings

Achieved energy sensitivity of approximately 10^{-4} for amplitude detection

Enabled detection of transfer function phase and amplitude over hundreds of MHz

Facilitated potential improvements in quantum gate fidelity and microwave field characterization

Abstract

Experiments with superconducting circuits require careful calibration of the applied pulses and fields over a large frequency range. This remains an ongoing challenge as commercial semiconductor electronics are not able to probe signals arriving at the chip due to its cryogenic environment. Here, we demonstrate how the on-chip amplitude and frequency of a microwave signal can be inferred from the ac Stark shifts of higher transmon levels. In our time-resolved measurements we employ Ramsey fringes, allowing us to detect the amplitude of the systems transfer function over a range of several hundreds of MHz with an energy sensitivity on the order of $10^{-4}$. Combined with similar measurements for the phase of the transfer function, our sensing method can facilitate pulse correction for high fidelity quantum gates in superconducting circuits. Additionally, the potential to characterize arbitrary microwave fields promotes applications in related areas of research, such as quantum optics or hybrid microwave systems including photonic, mechanical or magnonic subsystems.