Abstract
As quantum devices make steady progress towards intermediate scale and fault-tolerant quantum computing, it is essential to develop rigorous and efficient measurement protocols that account for known sources of noise. Most existing quantum characterization protocols such as gate-set tomography and randomized benchmarking assume the noise acting on the qubits is Markovian. However, this assumption is often not valid, as for the case of charge noise or hyperfine nuclear spin noise. Here, we present a general framework for quantum process tomography (QPT) in the presence of time-correlated noise. We further introduce fidelity benchmarks that quantify the relative strength of different sources of Markovian and non-Markovian noise. As an application of our method, we perform a comparative theoretical and experimental analysis of silicon spin qubits. We first develop a detailed noise model that accounts for the dominant sources of noise and validate the model against experimental data. Applying our framework for time-correlated QPT, we find that the number of independent parameters needed to characterize one- and two-qubit gates can be compressed by and , respectively, when compared to the fully generic case. These compressions reduce the amount of tomographic measurements needed in experiment, while also significantly speeding up numerical simulations of noisy quantum circuit dynamics compared to time-dependent Hamiltonian simulation. Using this compressed noise model, we find good agreement between our theoretically predicted process fidelities and two-qubit interleaved randomized benchmarking fidelities of 99.8% measured in recent experiments on silicon spin qubits. More broadly, our formalism can be directly extended to develop efficient and scalable tuning protocols for high-fidelity control of large arrays of quantum devices with non-Markovian noise.
- Received 14 August 2023
- Accepted 9 January 2024
DOI:https://doi.org/10.1103/PRXQuantum.5.010306
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
Will be supplied soon.Solid-state qubits based on superconducting circuits and spins in silicon are often plagued by slow drift and low-frequency noise that challenge conventional approaches to calibration and characterization. These noise sources display long time correlations that violate the standard assumption of Markovian noise. In this work, we develop a systematic approach to rapidly and efficiently characterize time-correlated noise sources in quantum gate operations. Our approach is experimentally validated against state-of-the-art experiments on silicon spin qubits.
Looking toward future work, we expect our approach to inform approaches to automatic tuning of quantum devices. Autotuning methods are crucially needed in solid-state qubit devices to enable the high-fidelity operation needed for continuous operation with quantum error correction. A further frontier is to adapt our results to quantum sources of non-Markovian noise such as nuclear spins and strongly coupled two-level systems.
