High Frequency Dynamics and Third Cumulant of Quantum Noise

TL;DR

This paper reports the first high-frequency measurement of the third cumulant of quantum noise in a tunnel junction, revealing how environmental effects influence non-Gaussian quantum fluctuations beyond classical charge transfer regimes.

Contribution

It provides the first experimental investigation of the third cumulant of quantum noise at high frequency, addressing environmental influences and zero-point fluctuation effects in quantum regimes.

Findings

Environmental effects significantly influence quantum noise measurements.

The third cumulant $S_3$ can be non-zero in the quantum regime.

Zero-point fluctuations maintain the equilibrium noise level $S_2= G \, \hbar \omega$.

Abstract

The existence of the third cumulant $S_{3}$ of voltage fluctuations has demonstrated the non-Gaussian aspect of shot noise in electronic transport. Until now, measurements have been performed at low frequency, \textit{i.e.} in the classical regime $\hbar \omega < eV, k_BT$ where voltage fluctuations arise from charge transfer process. We report here the first measurement of $S_3$ at high frequency, in the quantum regime $\hbar \omega > eV, k_BT$. In this regime, experiment cannot be seen as a charge counting statistics problem anymore. It raises central questions of the statistics of quantum noise: 1) the electromagnetic environment of the sample has been proven to strongly influence the measurement, through the possible modulation of the noise of the sample. What happens to this mechanism in the quantum regime? 2) For $\hbar \omega > eV$, the noise is due to zero point fluctuations and keeps its equilibrium value: $S_2= G \hbar \omega$ with $G$ the conductance of the sample. Therefore, $S_2$ is independent of the bias voltage and no photon is emitted by the conductor. Is it possible, as suggested by some theories, that $S_3 \neq 0$ in this regime? With regard to these questions, we give theoretical and experimental answers to the environmental effects showing that they involve dynamics of the quantum noise. Using these results, we investigate the question of the third cumulant of quantum noise in the a tunnel junction.