Efficient continuous wave noise spectroscopy beyond weak coupling

Abstract

The optimization of quantum control for physical qubits relies on accurate noise characterization. Probing the spectral density $S(\omega )$ of semi-classical phase noise using a spin interacting with a continuous-wave (CW) resonant excitation field has recently gained attention. CW noise spectroscopy protocols have been based on the generalized Bloch equations (GBE) or the filter function formalism, assuming weak coupling to a Markovian bath. However, this standard protocol can substantially underestimate $S(\omega )$ at low frequencies when the CW pulse amplitude becomes comparable to $S(\omega )$. Here, we derive the coherence decay function more generally by extending it to higher orders in the noise strength and discarding the Markov approximation. Numerical simulations show that this provides a more accurate description of the spin dynamics compared to a simple exponential decay, especially on short timescales. Exploiting these results, we devise a protocol that uses an experiment at a single CW pulse amplitude to extend the spectral range over which $S(\omega )$ can be reliably determined to $\omega =0$.

10 pages, 6 figures

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• Frame-Based Filter-Function Formalism for Quantum Characterization and Control
• Extending comb-based spectral estimation to multiaxis quantum noise
• The dynamical-decoupling-based spatiotemporal noise spectroscopy
• SchWARMA: A model-based approach for time-correlated noise in quantum circuits
• Estimation of the Laser Frequency Nosie Spectrum by Continuous Dynamical Decoupling
• Scalable quantum measurement error mitigation via conditional independence and transfer learning
• Filter Function Formalism and Software Package to Compute Quantum Processes of Gate Sequences for Classical Non-Markovian Noise