Non-Gaussian noise as a quantum environment

François Chapeau-Blondeau

Leigh Norris, Gerardo A. Paz-Silva, Lorenza Viola

We introduce open-loop quantum control protocols for characterizing the spectral properties of non-Gaussian noise, applicable to both classical and quantum dephasing environments. By engineering a multidimensional frequency comb via repetition of suitably designed pulse sequences, the desired high-order spectra may be related to observable properties of the qubit probe. We prove that access to a high time resolution is key to achieving spectral reconstruction over an extended bandwidth, overcoming the limitations of existing schemes. Non-Gaussian spectroscopy is demonstrated for a classical noise model describing quadratic dephasing at an optimal point, as well as a quantum spin-boson model out of equilibrium. In both cases, we obtain spectral reconstructions that accurately predict the qubit dynamics in the non-Gaussian regime.

Aritra Ghosh, Subhashish Banerjee, M. Bhattacharya

Efficient control of quantum devices requires the knowledge of their environmental noise, yet the commonly measured power spectrum does not fully characterize non-Gaussian fluctuations of realistic environments. Here we show that exceptional points (EPs) in the noise-averaged dephasing response can expose observable signatures of non-Gaussian statistics, distinguishing environments with identical lower-order statistics. We also introduce a theoretical model that describes dephasing environments in terms of identical independent noise sources while preserving the power spectrum. Given a calibrated single-source model, the largest EP order extracted from the measured dephasing response determines the number of sources and predicts the higher-order statistics of the combined noise. We illustrate an atomtronic readout that maps distinct EP signatures onto an evolving ensemble-averaged atomic interference pattern. Our results connect non-Hermitian dynamics to environmental noise statistics, providing a route to characterize noise in quantum devices used in computing, metrology, and precision measurement.

Youngkyu Sung, Félix Beaudoin, Leigh Norris +9 more

Most quantum control and quantum error-correction protocols assume that the noise causing decoherence is described by Gaussian statistics. However, the Gaussianity assumption breaks down when the quantum system is strongly coupled to a sparse environment or has a non-linear response to external degrees of freedom. Here, we experimentally validate an open-loop quantum control protocol that reconstructs the higher-order spectrum of a non-Gaussian dephasing process using a superconducting qubit as a noise spectrometer. This experimental demonstration of non-Gaussian noise spectroscopy protocol represents a major step towards the goal of demonstrating a complete noise spectral characterization of quantum devices.

David E. McClelland, N. Mavalvala, Roman Schnabel

Gregory A. L. White