48 research outputs found
Determination of tunneling charge via current measurements
We consider a tunnel junction between two arbitrary non-linear systems in any
dimension, which can be different. We show that the tunneling charge can be
detected using three alternative methods based on current measurements. Besides
being technically easier compared to noise measurements, these methods present
valuable advantages: they do not require the knowledge of the underlying
models, and some are accessible in the experimentally convenient low-voltage
regime, where heating effects are reduced. The first method is based on the AC
conductance, while the two others are based on photo-assisted current (PAC) and
can be implemented for any time-dependence of the tunneling amplitude. These
are promising for edge states in the regime of the fractional quantum Hall
effect (FQHE): the Hamiltonian does not have to be specified and can
incorporate non-universal interactions between the edges, and it is more
convenient to use an AC gate voltage rather than an AC bias. These methods
apply for instance to weak barriers in 1-D systems,
Superconductor-Insulator-Normal (SIN) or graphene-like structures.Comment: The form has been improved, with additional useful comments,
citations have been added. 7 pages, one figur
Shot noise of weak cotunneling current: Non-equilibrium fluctuation-dissipation theorem
We study the noise of the cotunneling current through one or several
tunnel-coupled quantum dots in the Coulomb blockade regime. We consider the
regime of weak (elastic and inelastic) cotunneling, and prove a non-equilibrium
fluctuation-dissipation theorem which leads to a universal expression for the
noise-to-current ratio (Fano factor).Comment: 5 pages, 1 figure, submitted for "Electronic Correlations: From meso-
to nano-physics", edited by G. Montambaux and T. Martin, XXXVI Rencontres de
Moriond, 200
Transport and Noise of Entangled Electrons
We consider a scattering set-up with an entangler and beam splitter where the
current noise exhibits bunching behavior for electronic singlet states and
antibunching behavior for triplet states. We show that the entanglement of two
electrons in the double-dot can be detected in mesoscopic transport
measurements. In the cotunneling regime the singlet and triplet states lead to
phase-coherent current contributions of opposite signs and to Aharonov-Bohm and
Berry phase oscillations in response to magnetic fields. We analyze the Fermi
liquid effects in the transport of entangled electrons.Comment: 9 pages, Latex, uses lamuphys.sty (included), 1 eps figure embedded
with epsf, to appear in Proceedings of the XVI Sitges Conference (Lecture
Notes in Physics, Springer
Stochastic Field Theory for Transport Statistics in Diffusive Systems
We present a field theory for the statistics of charge and current
fluctuations in diffusive systems. The cumulant generating function is given by
the saddle-point solution for the action of this field theory. The action
depends on two parameters only: the local diffusion and noise coefficients,
which naturally leads to the universality of the transport statistics for a
wide class of multi-dimensional diffusive models. Our theory can be applied to
semi-classical mesoscopic systems, as well as beyond mesoscopic physics.Comment: Submitted to the proceedings of the XXXIXth Rencontres de Moriond (La
Thuile, 2004) "Quantum information and decoherence in nanosystems
Fluctuation Statistics in Networks: a Stochastic Path Integral Approach
We investigate the statistics of fluctuations in a classical stochastic
network of nodes joined by connectors. The nodes carry generalized charge that
may be randomly transferred from one node to another. Our goal is to find the
time evolution of the probability distribution of charges in the network. The
building blocks of our theoretical approach are (1) known probability
distributions for the connector currents, (2) physical constraints such as
local charge conservation, and (3) a time-scale separation between the slow
charge dynamics of the nodes and the fast current fluctuations of the
connectors. We derive a stochastic path integral representation of the
evolution operator for the slow charges. Once the probability distributions on
the discrete network have been studied, the continuum limit is taken to obtain
a statistical field theory. We find a correspondence between the diffusive
field theory and a Langevin equation with Gaussian noise sources, leading
nevertheless to non-trivial fluctuation statistics. To complete our theory, we
demonstrate that the cascade diagrammatics, recently introduced by Nagaev,
naturally follows from the stochastic path integral. We extend the
diagrammatics to calculate current correlation functions for an arbitrary
network. One primary application of this formalism is that of full counting
statistics (FCS). We stress however, that the formalism is suitable for general
classical stochastic problems as an alternative to the traditional master
equation or Doi-Peliti technique. The formalism is illustrated with several
examples: both instantaneous and time averaged charge fluctuation statistics in
a mesoscopic chaotic cavity, as well as the FCS and new results for a
generalized diffusive wire.Comment: Final version accepted in J. Math. Phys. Discussion of conservation
laws, Refs., 1 Fig., and minor extensions added. 23 pages, 9 figs.,
double-column forma