High frequency dynamics and the third cumulant of quantum noise

The existence of the third cumulant S₃ of voltage fluctuations has demonstrated the non-Gaussian aspect of shot noise in electronic transport. Until now, measurements have been performed at low frequency, i.e. in the classical regime where voltage fluctuations arise from a charge transfer process. We report here the first measurement of S₃ at high frequency, in the quantum regime . In this regime, experimental results cannot be seen as a charge counting statistics problem any longer. This raises central questions as regards 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 , the noise is due to zero-point fluctuations and retains its equilibrium value: with G the conductance of the sample. Therefore, S₂ is independent of the bias voltage and no photon is emitted by the conductor. Is it possible, as suggested from some theories, that in this regime? For these questions, we give theoretical and experimental answers as regards the environmental effects, showing that they involve the dynamics of the quantum noise. Using these results, we investigate the question of the third cumulant of quantum noise in the tunnel junction.