Quantum Polyspectra for Uncompromising and Universal Evaluation of Quantum Measurements*

The analysis of a continuous measurement record poses a fundamental challenge in quantum measurement theory. Different approaches have been used in the past as records can, e.g., exhibit predominantly Gaussian noise, telegraph noise, or clicks at random times. This poster summarizes our latest findings, showing that quantum measurements from all the aforementioned cases can be analyzed in terms of higher-order temporal correlations of the detector output and be related to the Liouvillian of the measured quantum system. The comparison of temporal correlations via so-called quantum polyspectra is based on expressions derived without approximation from the stochastic master equation [1] and automated without requiring manual post-processing of the detector output. This allows for fitting of system parameters such as tunneling rates in a quantum transport experiment [2]. The very general stochastic master equation approach includes coherent quantum dynamics, environmental damping, and measurement backaction at arbitrary measurement strength. This enables a systematic evaluation of quantum measurements from the realms of conventional spin noise spectroscopy, quantum transport experiments, and, as our newest finding, ultra-weak measurements with stochastically arriving single photons [3,4]. [1] Hägele et al., PRB 98, 205143 (2018), [2] Sifft et al., PRR 3, 033123 (2021), [3] Sifft et al. PRA 107, 052203, [4] Sifft et al., arXiv:2310.10464