Two Qubit Correlated Noise and Crosstalk Characterization

Spatiotemporally correlated noise and crosstalk have a negative impact on error correcting schemes. We propose and validate a nonparametric quantum noise spectroscopy protocol to measure the spectra associated with spatiotemporally correlated dephasing noise and fluctuating crosstalk on two qubits. This method is also used to estimate the static components of the crosstalk and the dephasing noise processes acting on each qubit. Our scheme reconstructs the real and imaginary components of the two-qubit cross-spectrum by using two fixed total time pulse sequences and performing single qubit and joint two-qubit measurements to separately resolve spatially correlated noise processes from the individual noise spectra of the participating qubits. We benchmark our protocol by reconstructing the spectra of engineered spatiotemporally correlated noise processes produced by Schrodinger Wave Autoregressive Moving Average, a technique developed by our group [1] to generate phase error on qubit control lines. Our results demonstrate the utility of our protocol in characterizing spatiotemporally correlated noise and crosstalk in a multiqubit device for potential use in noise-adapted control or error mitigation schemes.

[1] Murphy, Andrew, et al. "Universal-dephasing-noise injection via Schrödinger-wave autoregressive moving-average models." Physical Review Research 4.1 (2022): 013081.