Plenarvorträge - DPG-Tagungen

Symposium Quantum Shot Noise in Nanostructures Montag
Fachsitzungen
– Haupt- und Kurzvorträge –
SYSN 1 Quantum Shot Noise in Nanostructures
Zeit: Montag 13:30–15:30 Raum: H1
Hauptvortrag SYSN 1.1 Mo 13:30 H1
Quantum Shot Noise in Nanostructures: From Schottky to Bell
— •Markus Büttiker — Département de Physique Theorique, Université
de Genève, CH-1211 Genéve 4, Switzerland.
For more than a decade, theoretical and experimental investigations
of noise properties have been at the forefront in our quest to understand
the transport properties of small electrical conductors. Initial work
aimed at characterizing shot noise with the help of Fano factors: the ratio
of the shot noise to full Poisson (Schottky) noise. Later the theory
was extended to include not only the second moment (shot noise) but
all higher order current correlations. We contrast fully quantum mechanical
approaches to this problem with semiclassical discussions. Current
fluctuations are often understood as simply a stochastic successive transfer
of particles. But an analysis of current-current fluctuations shows
that it is possible to invent geometries in which there is no Aharonov-
Bohm effect in the conductance (second order interference) but there is
very well an Aharonov-Bohm effect in noise-correlations (fourth order
interference). We demonstrate that this is a consequence of a two particle
Aharonov-Bohm effect: in the tunneling limit it can be connected
to orbitally entangled electron-hole states. We show that zero-frequency
noise-correlation measurements can be used to proof that these states
violate a Bell inequality.
Hauptvortrag SYSN 1.2 Mo 14:00 H1
Mesoscopic transition in the shot noise of diffusive SNS junctions
— •Francois Lefloch 1 , Christian Hoffmann 1 , Marc Sanquer
1 , and Bernard Pannetier 2 — 1 Département de Recherche
Fondamentale sur la Matière Condensée/SPSMS/LCP, CEA/Grenoble,
17 rue des Martyrs, 38054 Grenoble cedex 09, France — 2 Centre de
Recherches sur les Très Basses Températures-C.N.R.S. associated to Université
Joseph Fourier, 25 rue des Martyrs, 38042 Grenoble, France
We experimentally investigated the current noise in short diffusive Superconductor/Normal
metal/Superconductor junctions over a large range
of energy that covers the regimes of coherent and incoherent multiple Andreev
reflections. The transition between these two regimes, occurs at the
Thouless energy where a pronounced minimum in the current noise density
is observed. Above the Thouless energy, in the regime of incoherent
multiple Andreev reflections, the noise is very much enhanced compared
to a normal junction and grows linearly with the bias voltage. Semiclassical
theory describes accurately the experimental results over the
entire temperature range, but only if we take into account the voltage
dependence of the resistance which reflects the proximity effect. Below
the Thouless energy, the shot noise diverge as 1/eV and may indicate
the coherent transfer of multiple charges.
Hauptvortrag SYSN 1.3 Mo 14:30 H1
Quantum Noise: Challenge and Prospect — •Yuli V. Nazarov
— Department of NanoScience, Delft University of Technology,
Lorentzweg 1, 2628 CJ Delft, The Netherlands
The concept of full counting statistics does not just give a new dimension
to studies of electron transport: it gives it infinitely many dimensions.
To enter and conquer this new world is a challenge, better understanding
of nanophysics and quantum mechanics is the prospect.
SYSN 1.4 Mo 15:00 H1
Electron counting statistics and the Clauser-Horne inequality
— •Fabio Taddei 1 , Lara Faoro 2 , and Rosario Fazio 1 — 1 NEST-
INFM & Scuola Normale Superiore, Pisa, Italy — 2 ISI Foundation, Viale
Settimio Severo, 65, I-10133 Torino, Italy
We derive the Clauser-Horne (CH) inequality for the full electron
counting statistics in a mesoscopic multiterminal conductor and we discuss
its properties. We first consider the idealized situation in which a
flux of entangled electrons is generated by an entangler. Given a certain
average number of incoming entangled electrons, the CH inequality can
be evaluated for different numbers of transmitted particles. Strong violations
occur when the number of transmitted charges on the two terminals
is the same (Q1 = Q2), whereas no violation is found for Q1 �= Q2. We
then consider a three terminal normal beam splitter and a hybrid superconducting
structure. Interestingly, we find that the CH inequality is
violated for the three terminal normal device. As expected, we find full
violation of the CH inequality in the case of the superconducting system.
SYSN 1.5 Mo 15:15 H1
Suppression of shot noise by dynamical mechanisms —
•Henning Schomerus — MPIPKS Dresden, Nöthnitzer Str. 38, 01187
Dresden
The investigation of shot noise in mesoscopic systems has many merits,
one of the primary ones being the detection of system-specific details
that help to uncover dynamics and interactions. We identify three dynamical
mechanisms that reduce shot noise in ballistic quantum dots below
the universal prediction of random-matrix theory: a) direct processes, b)
dynamics along stable trajectories, and c) delay of diffraction for very
small wavelength. Mechanisms a) and b) are efficient means in the quest
to suppress shot noise in phase-coherent systems, while mechanism c)
elucidates the particle-wave duality and the correspondence principle in
the quantum-to-classical crossover.
[1] H.-S. Sim and H. Schomerus, Phys. Rev. Lett. 89, 066801 (2002).
[2] R. G. Nazmitdinov, H.-S. Sim, H. Schomerus, and I. Rotter, Phys.
Rev. B 66, 241302(R) (2002).
[3] J. Tworzydlo, A. Tajic, H. Schomerus, and C. W. J. Beenakker, Phys.
Rev. B 68, 115313 (2003).
SYSN 2 Quantum Shot Noise in Nanostructures
Zeit: Montag 16:00–17:45 Raum: H1
Hauptvortrag SYSN 2.1 Mo 16:00 H1
Environmental effects in the third moment of voltage fluctuations
in a tunnel junction — •Bertrand Reulet 1,2 , J. Senzier
1 , and Daniel E. Prober 1 — 1 Departments of Applied Physics
and Physics, Yale University, New Haven CT 06520-8284, USA —
2 Laboratoire de Physique des Solides, associé au CNRS, bâtiment 510,
Université Paris-Sud 91405 Orsay, France
We present the first measurements of the third moment of the voltage
fluctuations in a conductor. This technique can provide a new and complementary
information on the electronic transport in any kind of physical
system. The measurement was performed on non-superconducting
tunnel junctions as a function of voltage bias, for various temperatures
and frequency bandwidths up to 1GHz. The data demonstrate the importance
of the effect of the electromagnetic environment of the sample
on the voltage fluctuations.