GHz experiment in Mesoscopic Physics

1
Non-Gaussian Shot Noise in a Tunnel Junction in
the Quantum Regime
Julien Gabelli Bertrand Reulet
Laboratoire de Physique des Solides Bât. 510,
Université Paris-Sud, 91405 Orsay, France
Aussois 22/03/07
2
Current fluctuations in conductors
Characterized by the Noise spectral density S2 in
A2/Hz
But it is not sufficient
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Gaussian vs. Non-Gaussian Noise
Current fluctuations in a tunnel junction at zero
frequency (hDfltlteV)
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Current statistics frequency?
Difficulty central limit theorem P(i)
almost gaussian
Full counting statistics measurement of PT(i)
by digitalizing the current i(t)
Yu. Bomze, G. Gershon, D. Shovkun, L. S. Levitov,
and M. ReznikovPhys. Rev. Lett. 95, 176601
(2005)
well defined only at zero frequency, charge
counting
what happens below the characteristic time th/eV
, Quantum regime ?
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Frequency dependence S2(w)
Noise spectral density S2(w) at finite frequency
(??gtgtkBT)
beating between spectral components w and -w
T35 mK f6 GHz
Experimental Data²
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Higher order moments at finite frequency
Frequency dependent higher order moments, S3
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Higher order moments at finite frequency
Frequency dependent higher order moments, S3
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Experimental setup S3(?,0)
50 W Al/Al2O3/Al, 15 µm² Lafe Spietz, Yale
Measurement of S3(?, 0) ?f(HF) ?f(LF) with
imperfect voltage bias ? voltage fluctuations ?
feedback and noise of the environment
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Feedback and noise of the environment
measured voltage
shot noise V dependent
Independent of V
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Feedback and noise susceptibility
Example of fluctuations (at w1) due to
environment
Kindermann,Nazarov, Beenakker PRL 90, 176802
(2003)
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Noise susceptibility
Noise dynamics measured at ?2 when excited at ? 1
New correlation function
Calculated and measured for a tunnel junction in
the quantum limit ??gtgteV,kBT
The noise does not follow the excitation
Vac
Vdc
J. Gabelli and B. Reulet, unpublished
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Feedback and noise susceptibility
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Feedback and noise susceptibility
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Fitting parameters (S3 temperature independent)
Data at different temperatures
Fit
Fitting parameters
compatible measurements
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S3 measurement
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Conclusion
We demonstrate experimentally S3(?,0) e2 I,
independent of ? even if ?? gt eV
J. Salo, F. W. J. Hekking, J. P. Pekola
Very non intuitive result if we consider a
photo-detection scheme
what is S3 in the regime ?? lt eV ?
correlation between electrons and photons
Observed in Quantum optics cf Y. Yamamoto, P.
Grangier
what happens in the quantum regime ?? gt eV ?
no photon but S3?0
Is S3(??gteV)?0 due to zero point fluctuations
detected with a linear amplifier ?
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Thanks to NS2 team
Marco Aprili Francesca Chiodi Rossella
Latempa Ivana Petkovic Edgar Patino Bertrand
Reulet