Combating fluctuations in relaxation times of fixed-frequency transmon qubits with microwave-dressed states

TL;DR

This paper proposes using microwave-dressed states via off-resonance microwave drives to actively tune fixed-frequency transmon qubits, reducing relaxation time fluctuations caused by TLS defects and enhancing qubit stability.

Contribution

It introduces a method to tune transmon qubits by up to 20 MHz using ac-Stark shifts, actively mitigating TLS-induced fluctuations in fixed-frequency qubits.

Findings

Qubit frequency can be shifted up to 20 MHz with minimal control impact.

Microwave-dressed states effectively reduce relaxation time fluctuations.

Active tuning offers a new approach to improve qubit stability.

Abstract

With the long coherence time, the fixed-frequency transmon qubit is a promising qubit modality for quantum computing. Currently, diverse qubit architectures that utilize fixed-frequency transmon qubits have been demonstrated with high-fidelity gate performance. Nevertheless, the relaxation times of transmon qubits can have large temporal fluctuations, causing instabilities in gate performance. The fluctuations are often believed to be caused by nearly on-resonance couplings with sparse two-level-system (TLS) defects. To mitigate their impact on qubit coherence and gate performance, one direct approach is to tune the qubits away from these TLSs. In this work, to combat the potential TLS-induced performance fluctuations in a tunable-bus architecture unitizing fixed-frequency transmon qubits, we explore the possibility of using an off-resonance microwave drive to effectively tuning the qubit frequency through the ac-Stark shift while implementing universal gate operations on the microwave-dressed qubit. We show that the qubit frequency can be tuned up to 20 MHz through the ac-stark shift while keeping minimal impacts on the qubit control. Besides passive approaches that aim to remove these TLSs through more careful treatments of device fabrications, this work may offer an active approach towards mitigating the TLS-induced performance fluctuations in fixed-frequency transmon qubit devices.