Measuring the temperature dependence of individual two-level systems by direct coherent control

TL;DR

This paper introduces a novel technique for directly controlling and measuring the temperature-dependent coherence properties of individual two-level systems in phase qubits using microwave pulses, revealing quadratic temperature dependence of relaxation times.

Contribution

The work presents a new method for manipulating and characterizing single TLS in phase qubits, enabling direct measurement of temperature effects on their coherence.

Findings

Energy relaxation time T₁ decreases quadratically with temperature.

Dephasing time is T₁ limited across all temperatures.

First measurement of temperature dependence of TLS coherence.

Abstract

We demonstrate a new method to directly manipulate the state of individual two-level systems (TLS) in phase qubits. It allows one to characterize the coherence properties of TLS using standard microwave pulse sequences, while the qubit is used only for state readout. We apply this method to measure the temperature dependence of TLS coherence for the first time. The energy relaxation time $T_1$ is found to decrease quadratically with temperature for the two TLS studied in this work, while their dephasing time measured in Ramsey and spin-echo experiments is found to be $T_1$ limited at all temperatures.