Exponential sensitivity to dephasing of electrical conduction through a quantum dot

According to random-matrix theory, interference effects in the conductance of a ballistic chaotic quantum dot should vanish proportional to (tau(phi)/tau(D))(p) when the dephasing time tau(phi) becomes small compared to the mean dwell time tau(D). Aleiner and Larkin have predicted that the power law crosses over to an exponential suppression proportional to exp((-tau(E)/tau(phi)) when tau(phi) drops below the Ehrenfest time tau(E). We report the first observation of this crossover in a computer simulation of universal conductance fluctuations. Their theory also predicts an exponential suppression proportional to exp((-tau(E)/tau(D)) in the absence of dephasing--which is not observed. We show that the effective random-matrix theory proposed previously for quantum dots without dephasing explains both observations.     

Shot noise in ballistic quantum dots with a mixed classical phase space

We investigate shot noise for quantum dots whose classical phase space consists of both regular and chaotic regions. The noise is systematically suppressed below the universal value of fully chaotic systems, by an amount which varies with the positions of the leads. We analyze the dynamical origin of this effect by a novel way to incorporate diffractive impurity scattering. The dependence of the shot noise on the scattering rate shows that the suppression arises due to the deterministic nature of transport through regular regions and along short chaotic trajectories. Shot noise can be used to probe phase-space structures of quantum dots with generic classical dynamics.     

Superconducting terminals as sensitive probes for scarred states

When a quantum-chaotic normal conductor is coupled to a superconductor, the random-matrix theory (RMT) predicts that a gap opens up in the excitation spectrum which is of universal size E(g)(RMT) approximately 0.3 Planck/t(D), where t(D) is the mean scattering time between Andreev reflections. We show that a scarred state of long lifetime t(S)>t(D) suppresses the excitation gap over a window DeltaE approximately 2E(g)(RMT) which can be much larger than the narrow resonance width GammaS= Planck/t(S) of the scar in the normal system. The minimal value of the excitation gap within this window is given by GammaS/2相似文献   

Antibunched photons emitted by a quantum point contact out of equilibrium

Motivated by the experimental search for "GHz nonclassical light," we identify the conditions under which current fluctuations in a narrow constriction generate sub-Poissonian radiation. Antibunched electrons generically produce bunched photons, because the same photon mode can be populated by electrons decaying independently from a range of initial energies. Photon antibunching becomes possible at frequencies close to the applied voltage V x e/variant Planck's over 2pi, when the initial energy range of a decaying electron is restricted. The condition for photon antibunching in a narrow frequency interval below eV/variant Planck's over 2pi reads [SigmanTn(1-Tn)]2<2Sigman[Tn(1-Tn)]2, with Tn an eigenvalue of the transmission matrix. This condition is satisfied in a quantum point contact, where only a single Tn differs from 0 or 1. The photon statistics is then a superposition of binomial distributions.     

Anomalous wave function statistics on a one-dimensional lattice with power-law disorder

Within a general framework, we discuss the wave function statistics in the Lloyd model of Anderson localization on a one-dimensional lattice with a Cauchy distribution for random on-site potential. We demonstrate that already in leading order in the disorder strength, there exists a hierarchy of anomalies in the probability distributions of the wave function, the conductance, and the local density of states, for every energy which corresponds to a rational ratio of wavelength to lattice constant. Power-law rather than log-normal tails dominate the short-distance wave-function statistics.     

Search for two-scale localization in disordered wires in a magnetic field

A recent paper [A. V. Kolesnikov and K. B. Efetov, Phys. Rev. Lett. 83, 3689 (1999)] predicts a two-scale behavior of wave function decay in disordered wires in the crossover regime from preserved to broken time-reversal symmetry. We have tested this prediction by a transmission approach, relying on the Borland conjecture that relates the decay length of the transmittance to the decay length of the wave functions. Our numerical simulations show no indication of two-scale behavior.     

Counting statistics of photons produced by electronic shot noise

A theory is presented for the photodetection statistics of radiation produced by current fluctuations in a phase-coherent conductor. Deviations are found from the Poisson statistics that would result from a classical current. For detection in a narrow frequency interval delta omega, the photocount distribution has the negative-binomial form of blackbody radiation if e delta omega is less than the mean current I in the conductor. When electronic localization sets in, I drops below e delta omega and a different type of super-Poissonian photon statistics results.