Abstract
In order to characterize and calibrate quantum processing devices, a large amount of measurement data has to be collected. Active qubit reset increases the speed at which data can be gathered but requires additional hardware and/or calibration. The experimental apparatus can, however, be operated at elevated repetition rates without reset. In this case, the outcome of a first measurement serves as the initial state for the next experiment. Rol et al. have used this restless operation mode to accelerate the calibration of a single-qubit gate by measuring fixed-length sequences of Clifford gates that compose to gates [Phys. Rev. Appl. 7, 041001 (2017)]. However, we find that when measuring pulse sequences that compose to arbitrary operations, distortion appears in the measured data. Here, we extend the restless methodology by showing how to efficiently analyze restless measurements and correct distortions to achieve an identical outcome and accuracy as compared to measurements in which the superconducting qubits are reset. This allows us to rapidly characterize and calibrate qubits. We illustrate this bias-corrected restless measurements method by measuring a Rabi oscillation at a repetition rate without any reset, for a qubit with a decay rate of . We also show that we can measure a single- and a two-qubit average gate fidelity using randomized benchmarking 20 and 8 times faster, respectively, than measurements that reset the qubits through decay.
- Received 22 October 2020
- Revised 11 February 2021
- Accepted 18 March 2021
DOI:https://doi.org/10.1103/PRXQuantum.2.020324
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Calibration measurements require a significant portion of the available up time in current quantum computing systems. Here, we demonstrate how to speed up common single- and two-qubit characterization measurements such as Rabi oscillations and randomized benchmarking by deliberately omitting the qubit reset mechanism. Usually, reset of the qubits is achieved by taking advantage of the intrinsic ground-state decay, which accounts for up to 98% of the total run time of experimental sequences. By omitting the relaxation-based reset mechanism, we can speed up calibration and characterization measurements by factors of 20 for randomized benchmarking and 250 for Rabi-oscillation measurements. The speed limits are then exclusively set by the time it takes to execute the control sequence of the qubit.
We give a detailed description of the data analysis method that we develop to alleviate the effects of measuring the qubit without intermediate resets and present an in-depth performance analysis of our method in comparison to standard qubit readout procedures. We show that both speed and accuracy are comparable to alternative methods such as active qubit reset, all without the need for additional control hardware or real-time feedback.
