Higher Threshold Parameters in pi pi Scattering

A family of threshold parameters which probe the stability of chiral predictions is considered. The relevant criteria for the choice of threshold parameters are discussed. Sum rules for these quantities are derived from dispersion relations and evaluated from effective range formulae. Good agreement with two-loop chiral estimates for many of these quantities is found and interesting discrepancies are discussed.Comment: 15 pages, LaTe

Chaotic dot-superconductor analog of the Hanbury Brown Twiss effect

As an electrical analog of the optical Hanbury Brown Twiss effect, we study current cross-correlations in a chaotic quantum dot-superconductor junction. One superconducting and two normal reservoirs are connected via point contacts to a chaotic quantum dot. For a wide range of contact widths and transparencies, we find large positive current correlations. The positive correlations are generally enhanced by normal backscattering in the contacts. Moreover, for normal backscattering in the contacts, the positive correlations survive when suppressing the proximity effect in the dot with a weak magnetic field.Comment: 4 pages, 3 figure

Quantum capacitance: a microscopic derivation

We start from microscopic approach to many body physics and show the analytical steps and approximations required to arrive at the concept of quantum capacitance. These approximations are valid only in the semi-classical limit and the quantum capacitance in that case is determined by Lindhard function. The effective capacitance is the geometrical capacitance and the quantum capacitance in series, and this too is established starting from a microscopic theory.Comment: 7 fig

Semiclassical theory of current correlations in chaotic dot-superconductor systems

We present a semiclassical theory of current correlations in multiterminal chaotic dot-superconductor junctions, valid in the absence of the proximity effect in the dot. For a dominating coupling of the dot to the normal terminals and a nonperfect dot-superconductor interface, positive cross correlations are found between currents in the normal terminals. This demonstrates that positive cross correlations can be described within a semiclassical approach. We show that the semiclassical approach is equivalent to a quantum mechanical Green's function approach with suppressed proximity effect in the dot.Comment: 5 pages, 3 figure

Charge-Relaxation and Dwell Time in the fluctuating Admittance of a Chaotic Cavity

We consider the admittance of a chaotic quantum dot, capacitively coupled to a gate and connected to two electron reservoirs by multichannel ballistic point contacts. For a dot in the regime of weak-localization and universal conductance fluctuations, we calculate the average and variance of the admittance using random-matrix theory. We find that the admittance is governed by two time-scales: the classical admittance depends on the RC-time of the quantum dot, but the relevant time scale for the weak-localization correction and the admittance fluctuations is the dwell time. An extension of the circular ensemble is used for a statistical description of the energy dependence of the scattering matrix.Comment: 7 pages, RevTeX, 1 figur

Quantized dynamics of a coherent capacitor

A quantum coherent capacitor subject to large amplitude pulse cycles can be made to emit or reabsorb an electron in each half cycle. Quantized currents with pulse cycles in the GHz range have been demonstrated experimentally. We develop a non-linear dynamical scattering theory for arbitrary pulses to describe the properties of this very fast single electron source. Using our theory we analyze the accuracy of the current quantization and investigate the noise of such a source. Our results are important for future scientific and possible metrological applications of this source.Comment: 4 pages, 2 figure

Orbital entanglement and violation of Bell inequalities in the presence of dephasing

We discuss orbital entanglement in mesoscopic conductors, focusing on the effect of dephasing. The entanglement is detected via violation of a Bell Inequality formulated in terms of zero-frequency current correlations. Following closely the recent work by Samuelsson, Sukhorukov and Buttiker, we investigate how the dephasing affects the possibility to violate the Bell Inequality and how system parameters can be adjusted for optimal violation.Comment: 9 pages, 2 figures. To appear in a special issue on "Quantum Computation at the Atomic Scale" in Turkish Journal of Physic

pi K scattering inputs to ChPT

Experimental information on low energy $\pi K$ scattering would shed light on the poorly known OZI suppressed sector of ChPT. I describe recent work aimed at generating such information based on available experimental data by setting up and then solving with appropriate boundary conditions a non linear system of equations of the Roy and Steiner type. First results of this analysis are presented.Comment: Talk given at QCD'03 conference, 2-9 July 2003, Montpellie

Comment on "Observation of Spin Injection at a Ferromagnet-Semiconductor Interface, by P.R. Hammar et al

In a recent Letter Hammar et al. claim the observation of injection of a spin-polarized current in a two-dimensional electron gas (2DEG). This is an important observation, since, despite considerable effort of several groups, all attempts to realize spin-injection into a 2DEG using purely electrical measurements have failed sofar. However, in my opinion the claim made is not correct, and the observed behaviour can be explained by a combination of a magneto resistance (Hall) effect (e.g. generated by the fringe magnetic fields present at the edges of the ferromagnetic electrode), with a {\it spin-independent} rectification effect due to the presence of a metal- semiconductor junction.Comment: accepted for PRL, 1 pag

Interference in presence of Dissipation

We study a particle on a ring in presence of various dissipative environments. We develop and solve a variational scheme assuming low frequency dominance. We analyze our solution within a renormalization group (RG) scheme to all orders which reproduces a 2 loop RG for the Caldeira-Legget environment. In the latter case the Aharonov-Bohm (AB) oscillation amplitude is exponential in -R^2 where R is the ring's radius. For either a charge or an electric dipole coupled to a dirty metal we find that the metal induces dissipation, however the AB amplitude is ~ R^{-2} for large R, as for free particles. Cold atoms with a large electric dipole may show a crossover between these two behaviors.Comment: 5 pages, added motivations and reference