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

Whispering gallery modes in optical fibers based on reflectionless potentials

We consider an optical fiber with nanoscale variation of the effective fiber radius supporting whispering gallery modes slowly propagating along the fiber, and reveal that the radius variation can be designed to support reflectionless propagation of these modes. We show that reflectionless modulations can realize control of transmission amplitude and temporal delay, while enabling close packing due to the absence of cross-talk, in contrast to conventional potentials.Comment: 4 pages, 3 figure