Characterizing non-classical non-Gaussian noise: photon shot noise fluctuations*

Understanding how to accurately describe environmental noise is of crucial importance for designing control protocols that enable high-fidelity quantum operations. While standard approaches often assume classical Gaussian noise, going beyond these assumptions is important in many settings. Here, we consider both the non-classical and non-Gaussian nature of photon number fluctuations in a driven dissipative quantum resonator; such fluctuations can be a significant limitation on the performance of superconducting qubits. We extend the Keldysh approach for characterizing this quantum noise [1,2] to calculate its frequency-resolved third cumulant, the so-called bispectrum. We discuss how the quantum noise bispectrum directly reveals features of non-classicality and non-equilibrium bath dynamics. We also show how this quantum bispectrum could be measured using standard experimental tools in circuit QED.

[1] A. A. Clerk, Phys. Rev. A 84, 043824 (2011)
[2] P. P. Hofer and A. A. Clerk, Phys. Rev. Lett. 116, 013603 (2016)