Accelerated characterization of superconducting qubit relaxation times through modulated AC-Stark shifts 

The improvement of superconducting qubit performance typically relies on the batch characterization of devices while changes are made to optimize the device design, materials, and fabrication flow. However, owing in part to the slow frequency fluctuations of near-resonant two-level system (TLS) defects that deleteriously couple to these devices, the relaxation times of superconducting qubits are known to drift significantly on the timescale of days. To faithfully benchmark the performance of a particular design and fabrication scheme, then, it has become standard practice to aggregate measurements which are averaged over long timescales and for many copies of the same device. This greatly impedes the pace at which qubit designs, materials choices, and fabrication processes can be assessed. 

Here, we report on progress towards using the AC Stark shift to accelerate the benchmarking of superconducting qubits by varying the qubit frequency in time, mimicking the frequency drift of TLSs. In contrast to previous work, which has used external bias voltages or the averaged response of many discrete Stark shift measurements, we explore here time-dependent Stark drives that effectively smear the frequency of fixed-frequency transmon qubits over a single measurement. This may facilitate a significant speedup in the time required to assess the relaxation time of a given device. Furthermore, because, we drive the Stark shift through the qubit’s readout resonator as opposed to a dedicated charge line, this technique requires minimal hardware overhead.