# Service de Physique de l'Etat Condensé

Dynamics and Third Cumulant of Quantum Noise
Julien Gabelli
Laboratoire de Physique des Solides, UMR8502 Bât.510, Université Paris-Sud
Mercredi 28/01/2009, 11:15
SPEC Salle Itzykson, Bât.774, Orme des Merisiers
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, in particular: \begin{enumerate} \item 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? \item For $eV < \hbar \omega$, 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. It is possible, as suggested by some theories \cite{Zaikin,Hekking}, that $S_3 \neq 0$ in this regime? \end{enumerate} \noindent With regard to these questions, we give theoretical and experimental answers to the environmental effects showing 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. \begin{thebibliography}{} \bibitem{Zaikin} A. Galaktionov, D. Golubev, and A. Zaikin, Statistics of current fluctuations in mesoscopic coherent conductors at nonzero frequencies,{\em Phys. Rev. B} {\bf 68} pp. 235333 (2003) \bibitem{Hekking} J. Salo, F. W. J. Hekking, and J. P. Pekola , Frequency-dependent current correlation functions from scattering theory, {\em Phys. Rev. B} {\bf 74} pp. 125427 (2006) \end{thebibliography}
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