Optical Probe of Quantum Shot Noise Reduction at a Single-Atom Contact

Visible and infra-red light emitted at a Ag-Ag(111) junction has been investigated from tunneling to single atom contact conditions with a scanning tunneling microscope. The light intensity varies in a highly nonlinear fashion with the conductance of the junction and exhibits a minimum at conductances close to the conductance quantum. The data are interpreted in terms of current noise at optical frequencies, which is characteristic of partially open transport channels

Entanglement in a Noninteracting Mesoscopic Structure

We study the time dependent electron-electron and electron-hole correlations in a mesoscopic device which is splitting an incident current of free fermions into two spatially separated particle streams. We analyze the appearance of entanglement as manifested in a Bell inequality test and discuss its origin in terms of local spin-singlet correlations already present in the initial channel and the action of post-selection during the Bell type measurement. The time window over which the Bell inequality is violated is determined in the tunneling limit and for the general situation with arbitrary transparencies. We compare our results with alternative Bell inequality tests based on coincidence probabilities.Comment: 9 pages, 2 figure

Superconductor-metal transition in an ultrasmall Josephson junction biased by a noisy voltage source

Shot noise in a voltage source changes the character of the quantum (dissipative) phase transition in an ultrasmall Josephson junction: The superconductor-insulator transition transforms into the superconductor-metal transition. In the metallic phase the IV curve probes the voltage distribution generated by shot noise, whereas in the superconducting phase it probes the counting statistics of electrons traversing the noise junction.Comment: 4 pages, 3 figures. Corrected typos and style, added reference

A Josephson junction as a detector of Poissonian charge injection

We propose a scheme of measuring the non-Gaussian character of noise by a hysteretic Josephson junction in the macroscopic quantum tunnelling (MQT) regime. We model the detector as an (under)damped $LC$ resonator. It transforms Poissonian charge injection into current through the detector, which samples the injection statistics over a floating time window of length $\sim Q/\omega _{\rm J}$, where $Q$ is the quality factor of the resonator and $\omega_{\rm J}$ its resonance frequency. This scheme ought to reveal the Poisson character of charge injection in a detector with realistic parameters

Quantum conductance fluctuations in 3D ballistic adiabatic wires.

Quantum conductance of 3D ballistic wires with idealy flat boundaries obeys fluctuations with the properties quite distinguishable from those of universal conductance fluctuations: Both their amplitude and the sensitivity to the magnetic field flux $\Phi =HS$ penetrated into the sample cross-sectional area $S$ are different and depend on details of the cross-sectioanl shape of the wire. When the latter is integrable, conductance fluctuations have the enlarged amplitude $\delta G\sim\left[(e^2/h)^3G\right]^{1/4}$. When the cross-sectional shape of a wire is non-integrable, the irregular part of a conductance has the $e^ 2/h$ scale, whereas the correlation field is reduced to the value of $H_S\sim (\lambda_F/\sqrt S)^{1/2}(\Phi_0/S)$ and the correlation voltage of the nonlinear conductance fluctuations has the scale of $eV_c\sim\hbar^2/mS\sim E_F/(S/\lambda_F)$, where $\lambda_F=1/p_F$ is the Fermi wavelength.Comment: 5 pages, no pictures, to be published in "Coulomb and Interference Effects in Small Electronic Structures", ed. by D.Glattli, M.Sanquer and J.T.T.Van