Abstract
Transmon qubits experience open-system effects that manifest as noise at a broad range of frequencies. We present a model of these effects using the Redfield master equation with a hybrid bath consisting of low- and high-frequency components. We use two-level fluctuators to simulate -like noise behavior, which is a dominant source of decoherence for superconducting qubits. By measuring quantum state fidelity under free evolution with and without dynamical decoupling (DD), we can fit the low- and high-frequency noise parameters in our model. We train and test our model using experiments on quantum devices available through IBM quantum experience. Our model accurately predicts the fidelity decay of random initial states, including the effect of DD pulse sequences. We compare our model with two simpler models and confirm the importance of including both high frequency and noise in order to accurately predict transmon behavior.
- Received 16 March 2023
- Revised 26 October 2023
- Accepted 16 January 2024
DOI:https://doi.org/10.1103/PRXQuantum.5.010320
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
Quantum computing represents the next frontier in our technological advancement, with the potential to solve problems that are far beyond the reach of current computers. At the heart of these powerful machines are quantum bits (qubits), with transmon qubits being one of the most promising types for building a quantum computer. However, a significant hurdle in harnessing their full potential is “noise”—unwanted disturbances that introduce errors and can disrupt quantum calculations. Modeling this noise is essential for designing optimal control schemes that can suppress its effects. Past studies have taken several approaches to modeling the noise, but all have some drawbacks. Our work tackles the crucial question of how to model this noise both rigorously and resource efficiently.
We develop a new method to understand and model the impact of noise on transmon qubits. Traditional methods have either oversimplified the problem or have been too resource intensive to be practical. Most of the literature represents the noise with Pauli-like operators in a Markovian master equation, which fails to capture the non-Markovian nature of some noise and oversimplifies the multilevel transmon Hamiltonian. In our work, we propose and implement a simple noise modeling procedure that captures both the noise strength and frequency along different axes using a few simple free-evolution and dynamical decoupling experiments. We start with a model with a small number of free parameters consisting of both a quantum and a classical bath. By conducting a series of straightforward experiments, we show that the model can predict the fidelity decay of random initial states with and without dynamical decoupling pulses.
This innovation is not just limited to transmon qubits; it can be adapted to various types of qubits with minimal adjustments. Considering that our noise-learning method requires a small number of measurements and is broadly applicable, we expect that it will become a useful methodology for labs in their analysis of how the noise afflicting their experimental systems evolves as a function of time, which full noise spectroscopy is too slow to do effectively. Our method can also be used as part of processor calibration routines and can be repeated several times throughout the calibration cycle itself. This method will detect drift in the calibration and can be used to quickly quantify changes in the noise characteristics.
