Quantum Sensors for Microscopic Tunneling Systems

TL;DR

This paper introduces a method to detect and control individual tunneling Two-Level-Systems (TLS) in thin-film materials using superconducting qubits, aiding the development of low-loss quantum materials.

Contribution

It presents a novel hybrid quantum system approach for spectroscopic characterization of individual TLS in various materials.

Findings

Demonstrated spectroscopic detection of TLS resonances.

Evaluated TLS coupling to strain and electric fields.

Found evidence of strong interactions between TLS.

Abstract

The anomalous low-temperature properties of glasses arise from intrinsic excitable entities, so-called tunneling Two-Level-Systems (TLS), whose microscopic nature has been baffling solid-state physicists for decades. TLS have become particularly important for micro-fabricated quantum devices such as superconducting qubits, where they are a major source of decoherence. Here, we present a method to characterize individual TLS in virtually arbitrary materials deposited as thin-films. The material is used as the dielectric in a capacitor that shunts the Josephson junction of a superconducting qubit. In such a hybrid quantum system the qubit serves as an interface to detect and control individual TLS. We demonstrate spectroscopic measurements of TLS resonances, evaluate their coupling to applied strain and DC-electric fields, and find evidence of strong interaction between coherent TLS in the sample material. Our approach opens avenues for quantum material spectroscopy to investigate the structure of tunneling defects and to develop low-loss dielectrics that are urgently required for the advancement of superconducting quantum computers.