A scanning resonator for probing quantum coherent devices

TL;DR

This paper introduces a scanning resonator technique for probing quantum devices, enabling high-sensitivity, tunable measurements of qubits and materials without on-chip fabrication, at milliKelvin temperatures.

Contribution

The authors develop a tunable scanning resonator system that allows non-invasive, high-resolution characterization of quantum coherent devices and qubits without on-chip resonator fabrication.

Findings

Resonator internal quality factor > 10000 in the single-photon regime

Capacitive imaging with zeptoFarad sensitivity and micron resolution

Successful characterization of transmon qubits' energy spectrum and coherence times

Abstract

Superconducting resonators with high quality factors are extremely sensitive detectors of the complex impedance of materials and devices coupled to them. This capability has been used to measure losses in multiple different materials and, in the case of circuit quantum electrodynamics (circuit QED), has been used to measure the coherent evolution of multiple different types of qubits. Here, we report on the implementation of a scanning resonator for probing quantum coherent devices. Our scanning setup enables tunable coherent coupling to systems of interest without the need for fabricating on-chip superconducting resonators. We measure the internal quality factor of our resonator sensor in the single-photon regime to be > 10000 and demonstrate capacitive imaging using our sensor with zeptoFarad sensitivity and micron spatial resolution at milliKelvin temperatures. We then use our setup to characterize the energy spectrum and coherence times of multiple transmon qubits with no on-chip readout circuitry. Our work introduces a new tool for using circuit QED to measure existing and proposed qubit platforms.