What do phase space methods tell us about disordered quantum systems?

Introduction Phase space methods in quantum mechanics - The Wigner function - The Husimi function - Inverse participation ratio Anderson model in phase space - Husimi functions - Inverse participation ratiosComment: 14 pages, 4 figures. To be published in "The Anderson Transition and its Ramifications - Localisation, Quantum Interference, and Interactions", ed. by T. Brandes and S. Kettemann, Lecture Notes in Physics (http://link.springer.de/series/lnpp/) (Springer Verlag, Berlin-Heidelberg-New York

Conductance fluctuations in metallic nanogaps made by electromigration

We report on low temperature conductance measurements of gold nanogaps fabricated by controlled electromigration. Fluctuations of the conductance due to quantum interferences and depending both on bias voltage and magnetic field are observed. By analyzing the voltage and magnetoconductance correlation functions we determine the type of electron trajectories generating the observed quantum interferences and the effective characteristic time of phase coherence in our device.Comment: 5 pages, 4 figures, to appear in J. Appl. Phy

Coherent phonon dynamics at the martensitic phase transition of Ni_2MnGa

We use time-resolved optical reflectivity to study the laser stimulated dynamics in the magnetic shape memory alloy Ni_2MnGa. We observe two coherent optical phonons, at 1.2 THz in the martensite phase and at 0.7 THz in the pre-martensite phase, which we interpret as a zone-folded acoustic phonon and a heavily damped amplitudon respectively. In the martensite phase the martensitic phase transition can be induced by a fs laser pulse on a timescale of a few ps.Comment: 3 figure

Promoting a Shared Vision: Identifying Intersections Between Food and Fiber Systems Literacy Benchmarks and Illinois State Board of Education Standards

Understanding of agricultural systems has been an accepted and necessary aspect of a child’s education for centuries. Conventional agricultural education has proven effective in creating well-trained agricultural professionals and scholars, but has had the unintentional effect of limiting access to agricultural concepts to the non-agricultural student. This effect has potentially negative cultural consequences considering the importance agricultural issues. In response, agricultural educators have carried out an initiative to promote agricultural literacy in the classroom through an integration of agricultural concepts into core curriculum. A Guide to Food and Fiber Systems Literacy Benchmarks (Leising, 1998) is an example of programs that assess students’ level of agricultural literacy. However, integration of agricultural concepts into core curriculum without undermining state required standards is considered a primary obstacle in reaching goals in agricultural literacy. This research article uses the conceptual model proposed by Agnew, Powell, & Trexler (2008) which promotes a clarified vision for joining the differing educational paradigms. In particular, this article uses the method of exploring intersections in food and fiber systems literacy benchmarks with Illinois State Board of Education performance indicators in order to construct simple and comprehensive lesson units that meet both sets of educational standards

Low noise buffer amplifiers and buffered phase comparators for precise time and frequency measurement and distribution

Extremely low noise, high performance, wideband buffer amplifiers and buffered phase comparators were developed. These buffer amplifiers are designed to distribute reference frequencies from 30 KHz to 45 MHz from a hydrogen maser without degrading the hydrogen maser's performance. The buffered phase comparators are designed to intercompare the phase of state of the art hydrogen masers without adding any significant measurement system noise. These devices have a 27 femtosecond phase stability floor and are stable to better than one picosecond for long periods of time. Their temperature coefficient is less than one picosecond per degree C, and they have shown virtually no voltage coefficients

Primary tunnel junction thermometry

We describe the concept and experimental demonstration of primary thermometry based on a four probe measurement of a single tunnel junction embedded within four arrays of junctions. We show that in this configuration random sample specific and environment-related errors can be avoided. This method relates temperature directly to Boltzmann constant, which will form the basis of the definition of temperature and realization of official temperature scales in the future

The Bright Side of Coulomb Blockade

We explore the photonic (bright) side of dynamical Coulomb blockade (DCB) by measuring the radiation emitted by a dc voltage-biased Josephson junction embedded in a microwave resonator. In this regime Cooper pair tunneling is inelastic and associated to the transfer of an energy 2eV into the resonator modes. We have measured simultaneously the Cooper pair current and the photon emission rate at the resonance frequency of the resonator. Our results show two regimes, in which each tunneling Cooper pair emits either one or two photons into the resonator. The spectral properties of the emitted radiation are accounted for by an extension to DCB theory.Comment: 4 pages, 4 figures + 3 pages, 1 figure supplementary materia

Macroscopic quantum tunneling in globally coupled series arrays of Josephson junctions

We present a quantitative analysis of an escape rate for switching from the superconducting state to a resistive one in series arrays of globally coupled Josephson junctions. A global coupling is provided by an external shunting impedance. Such an impedance can strongly suppress both the crossover temperature from the thermal fluctuation to quantum regimes, and the macroscopic quantum tunneling (MQT) in short Josephson junction series arrays. However, in large series arrays we obtain an enhancement of the crossover temperature, and a giant increase of the MQT escape rate. The effect is explained by excitation of a {\it spatial-temporal charge instanton} distributed over a whole structure. The model gives a possible explanation of recently published experimental results on an enhancement of the MQT in single crystals of high-$T_c$ superconductors.Comment: 4 pages, 3 figure

Evidence of Cooper pair pumping with combined flux and voltage control

We have experimentally demonstrated pumping of Cooper pairs in a single-island mesoscopic structure. The island was connected to leads through SQUID (Superconducting Quantum Interference Device) loops. Synchronized flux and voltage signals were applied whereby the Josephson energies of the SQUIDs and the gate charge were tuned adiabatically. From the current-voltage characteristics one can see that the pumped current increases in 1e steps which is due to quasiparticle poisoning on the measurement time scale, but we argue that the transport of charge is due to Cooper pairs.Comment: 4 page

A new non-perturbative approach to Quantum Brownian Motion

Starting from the Caldeira-Leggett (CL) model, we derive the equation describing the Quantum Brownian motion, which has been originally proposed by Dekker purely from phenomenological basis containing extra anomalous diffusion terms. Explicit analytical expressions for the temperature dependence of the diffusion constants are derived. At high temperatures, additional momentum diffusion terms are suppressed and classical Langivin equation can be recovered and at the same time positivity of the density matrix(DM) is satisfied. At low temperatures, the diffusion constants have a finite positive value, however, below a certain critical temperature, the Master Equation(ME) does not satisfy the positivity condition as proposed by Dekker.Comment: 5 page