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

M Kristen,X Wu,A Schneider,A Stehli,J Long,M Weides,A V Ustinov,D P Pappas,R Lake,S Danilin,H S Ku,T Wolz

doi:10.1038/s41534-020-00287-w

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.

Highlights

Implementing a fault-tolerant quantum processor requires gate fidelities far exceeding a threshold of 99%1–4
The collective response of all microwave components to an incident signal is described by the transfer function of the system
If the transfer function is known, digital signal processing techniques allow for full control over the shape of applied pulses

Summary

Introduction

Implementing a fault-tolerant quantum processor requires gate fidelities far exceeding a threshold of 99%1–4. In superconducting qubits, these gates are realized by on or near-resonant microwave pulses[5]. On the way to the circuit, the shape of these pulses is distorted by multiple passive microwave components such as attenuators, circulators and wires. These distortions negatively affect the gate fidelities if they are not accounted for. The collective response of all microwave components to an incident signal is described by the transfer function of the system. If the transfer function is known, digital signal processing techniques allow for full control over the shape of applied pulses

Methods

Results

Conclusion