Interacting Defects Generate Stochastic Fluctuations in Superconducting Qubits

TL;DR

This study investigates how interactions among two-level systems in amorphous dielectrics cause stochastic fluctuations in superconducting qubits, combining long-term measurements with simulations to understand the underlying physics.

Contribution

It introduces a comprehensive model explaining stochastic fluctuations in qubits due to TLS interactions, supported by experimental data and extensive simulations.

Findings

Stochastic fluctuations in qubits are caused by TLS interactions.

Low-frequency TLSs are about 1000 times more numerous than high-frequency TLSs.

Simulations accurately reproduce experimental fluctuation patterns.

Abstract

Amorphous dielectric materials have been known to host two-level systems (TLSs) for more than four decades. Recent developments on superconducting resonators and qubits enable detailed studies on the physics of TLSs. In particular, measuring the loss of a device over long time periods (a few days) allows us to investigate stochastic fluctuations due to the interaction between TLSs. We measure the energy relaxation time of a frequency-tunable planar superconducting qubit over time and frequency. The experiments show a variety of stochastic patterns that we are able to explain by means of extensive simulations. The model used in our simulations assumes a qubit interacting with high-frequency TLSs, which, in turn, interact with thermally activated low-frequency TLSs. Our simulations match the experiments and suggest the density of low-frequency TLSs is about three orders of magnitude larger than that of high-frequency ones.