Environmental effects in the third moment of voltage fluctuations in a tunnel junction

We present the first measurements of the third moment of the voltage fluctuations in a conductor. This technique can provide new and complementary information on the electronic transport in conducting systems. The measurement was performed on non-superconducting tunnel junctions as a function of voltage bias, for various temperatures and bandwidths up to 1GHz. The data demonstrate the significant effect of the electromagnetic environment of the sample.Comment: Major revision. More experimental results. New interpretation. 4 pages, 3 figure

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

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

Two-junction superconductor-normal metal single-electron trap in a combined on-chip RC environment

Dissipative properties of the electromagnetic environment as well as on-chip RC filtering are shown to suppress random state switchings in the two-junction superconductor(S) - normal metal(N) electron trap. In our experiments, a local high-ohmic resistor increased the hold time of the trap by up to two orders of magnitude. A strong effect of on-chip noise filtering was observed for different on-chip geometries. The obtained results are promising for realization of the current standard on the basis of the S-N hybrid turnstile.Comment: 4 pages 3 figures LT2

Quantum percolation in granular metals

Theory of quantum corrections to conductivity of granular metal films is developed for the realistic case of large randomly distributed tunnel conductances. Quantum fluctuations of intergrain voltages (at energies E much below bare charging energy scale E_C) suppress the mean conductance \bar{g}(E) much stronger than its standard deviation \sigma(E). At sufficiently low energies E_* any distribution becomes broad, with \sigma(E_*) ~ \bar{g}(E_*), leading to strong local fluctuations of the tunneling density of states. Percolative nature of metal-insulator transition is established by combination of analytic and numerical analysis of the matrix renormalization group equations.Comment: 6 pages, 5 figures, REVTeX

Density of states in a superconductor carrying a supercurrent

We have measured the tunneling density of states (DOS) in a superconductor carrying a supercurrent or exposed to an external magnetic field. The pair correlations are weakened by the supercurrent, leading to a modification of the DOS and to a reduction of the gap. As predicted by the theory of superconductivity in diffusive metals, we find that this effect is similar to that of an external magnetic field.Comment: To be published in Physical Review Letter

Classical limit of master equation for harmonic oscillator coupled to oscillator bath with separable initial conditions

The equation for the Wigner function describing the reduced dynamics of a single harmonic oscillator, coupled to an oscillator bath, was obtained by Karrlein and Grabert [Phys. Rev. E, vol. 55, 153 (1997)]. It was shown that for some special correlated initial conditions the equation reduces, in the classical limit, to the corresponding classical Fokker-Planck equation obtained by Adelman [J. Chem Phys., vol. 64, 124 (1976)]. However for separable initial conditions the Adelman equations were not recovered. We resolve this problem by showing that, for separable initial conditions, the classical Langevin equation obtained from the oscillator bath model is somewhat different from the one considered by Adelman. We obtain the corresponding Fokker-Planck equation and show that it exactly matches the classical limit of the equation for the Wigner function obtained from the master equation for separable initial conditions. We also discuss why the special correlated initial conditions correspond to Adelman's solution.Comment: 12 page

Characteristics associated with inappropriate hospital use in elderly patients admitted to a general internal medicine service

Our objective was to identify patient characteristics associated with inappropriate hospital days in a cohort of elderly medical inpatients. This prospective cohort study included a total of 196 patients aged 75 years and older, who were consecutively admitted over eight months to the internal medicine service of a regional, non-academic public hospital located in a rural area of Western Switzerland. Patients with severe cognitive impairment, terminal disease, or previously living in a nursing home were excluded. Data on demographics, medical, physical, social and mental status were collected at admission. A blinded hospitalization review was performed concurrently using a modified version of the Appropriateness Evaluation Protocol (AEP). Subjects' mean age was 82.4 years; 63.3% were women. Median length of stay was 8 days. Overall, 68 patients (34.7%) had at least one inappropriate day during their stay, including 18 patients (9.2%) whose hospital admission and entire stay were considered inappropriate. Most inappropriate days were due to discharge delays (87.1%), primarily to nursing homes (59.3%). Univariate analysis showed that subjects with inappropriate days were more likely to be living alone (69.1 vs 48.4%, p=0.006), and receiving formal in-home help (48.5 vs 32.8%, p=0.031). In addition, they were more impaired in basic and instrumental activities of daily living BADLs, and IADLs, p<0.001 and p=0.015, respectively), and more frequently had a depressed mood [29.4 vs 10.9%, p=0.001 with a score ≥ 6 at the Geriatric Depression Scale (GDS), short form]. Using multivariate analysis, independent associations remained for patients living alone (OR 2.6, 95%CI 1.2-5.8, p=0.016), those with a depressed mood (OR 2.8, 95%CI 1.1-7.3, p=0.032), with BADL dependencies (OR 1.5, 95%CI 1.2-1.8, p=0.001), and IADL dependencies (OR 1.3, 95%CI 1.0-1.6, p=0.032). Cardiovascular (OR 0.2, 95%CI 0.1-0.7, p=0.008) and pulmonary admission diagnoses (OR 0.1, 95%CI 0.0-0.7, p=0.022) were inversely associated with inappropriate hospital days. In conclusion, patients living alone, functionally impaired and showing depressive symptoms were at increased risk for inappropriate hospital days. These characteristics might permit better targeting for early discharge planning in these at-risk subjects, and contribute to avoiding premature discharge of other vulnerable elderly patients. Whether these interventions for at-risk patients will also result in prevention of hospitalization hazards, such as deconditioning and related functional decline, will require further stud

Tunneling into Nonequilibrium Luttinger Liquid with Impurity

We evaluate tunneling rates into/from a voltage biased quantum wire containing weak backscattering defect. Interacting electrons in such a wire form a true nonequilibrium state of the Luttinger liquid (LL). This state is created due to inelastic electron backscattering leading to the emission of nonequilibrium plasmons with typical frequency $\hbar \omega \leq U$. The tunneling rates are split into two edges. The tunneling exponent at the Fermi edge is positive and equals that of the equilibrium LL, while the exponent at the side edge $E_F-U$ is negative if Coulomb interaction is not too strong.Comment: 4+ pages, 5 figure

Collective transport in the insulating state of Josephson junction arrays

We investigate collective Cooper-pair transport of one- and two-dimensional Josephson junction arrays in the insulating state. We derive an analytical expression for the current-voltage characteristic revealing thermally activated conductivity at small voltages and threshold voltage depinning. The activation energy and the related depinning voltage represent a dynamic Coulomb barrier for collective charge transfer over the whole system and scale with the system size. We show that both quantities are non-monotonic functions of magnetic field. We propose that formation of the dynamic Coulomb barrier as well as the size scaling of the activation energy and the depinning threshold voltage, are consequences of the mutual phase synchronization. We apply the results for interpretation of experimental data in disordered films near the superconductor-insulator transition.Comment: 4 pages, 2 figures; typos corrected, new figures, an improved fit to experimental dat