11,690 research outputs found
Internal Josephson-Like Tunneling in Two-Component Bose-Einstein Condensates Affected by Sign of the Atomic Interaction and External Trapping Potential
We study the Josephson-like tunneling in two-component Bose-Einstein
condensates coupled with microwave field in respond to various attractive and
repulsive atomic interaction under the various aspect ratio of trapping
potential and the gravitational field. It is very interesting to find that the
dynamic of Josephson-like tunneling can be controlled from fast damped
oscillations and asymmetric occupation to nondamped oscillation and symmetric
occupation.Comment: 4 pages, 5 figure
Ratchet-like dynamics of fluxons in annular Josephson junctions driven by bi-harmonic microwave fields
Experimental observation of the unidirectional motion of a topological
soliton driven by a bi-harmonic ac force of zero mean is reported. The
observation is made by measuring the current-voltage characteristics for a
fluxon trapped in an annular Josephson junction that was placed into a
microwave field. The measured dependence of the fluxon mean velocity (rectified
voltage) at zero dc bias versus the phase shift between the first and second
harmonic of the driving force is in qualitative agreement with theoretical
expectations.Comment: 6 figure
Low-temperature transport through a quantum dot between two superconductor leads
We consider a quantum dot coupled to two BCS superconductors with same gap
energies . The transport properties are investigated by means of
infinite- noncrossing approximation. In equilibrium density of states, Kondo
effect shows up as two sharp peaks around the gap bounds. Application of a
finite voltage bias leads these peaks to split, leaving suppressed peaks near
the edges of energy gap of each lead. The clearest signatures of the Kondo
effect in transport are three peaks in the nonlinear differential conductance:
one around zero bias, another two at biases . This result is
consistent with recent experiment. We also predict that with decreasing
temperature, the differential conductances at biases anomalously
increase, while the linear conductance descends.Comment: replaced with revised versio
Statistics of voltage fluctuations in resistively shunted Josephson junctions
The intrinsic nonlinearity of Josephson junctions converts Gaussian current
noise in the input into non-Gaussian voltage noise in the output. For a
resistively shunted Josephson junction with white input noise we determine
numerically exactly the properties of the few lowest cumulants of the voltage
fluctuations, and we derive analytical expressions for these cumulants in
several important limits. The statistics of the voltage fluctuations is found
to be Gaussian at bias currents well above the Josephson critical current, but
Poissonian at currents below the critical value. In the transition region close
to the critical current the higher-order cumulants oscillate and the voltage
noise is strongly non-Gaussian. For coloured input noise we determine the third
cumulant of the voltage.Comment: 9 pages, 5 figure
High Frequency Quantum Admittance and Noise Measurement with an On-chip Resonant Circuit
By coupling a quantum detector, a superconductor-insulator-superconductor
junction, to a Josephson junction \textit{via} a resonant circuit we probe the
high frequency properties, namely the ac complex admittance and the current
fluctuations of the Josephson junction at the resonant frequencies. The
admittance components show frequency dependent singularities related to the
superconducting density of state while the noise exhibits a strong frequency
dependence, consistent with theoretical predictions. The circuit also allows to
probe separately the emission and absorption noise in the quantum regime of the
superconducting resonant circuit at equilibrium. At low temperature the
resonant circuit exhibits only absorption noise related to zero point
fluctuations, whereas at higher temperature emission noise is also present.Comment: 15 pages, 15 figure
Superconductive pumping of nanomechanical vibrations
We demonstrate that a supercurrent can pump energy from a battery that
provides a voltage bias into nanomechanical vibrations. Using a device
containing a nanowire Josephson weak link as an example we show that a
nonlinear coupling between the supercurrent and a static external magnetic
field leads to a Lorentz force that excites bending vibrations of the wire at
resonance conditions. We also demonstrate the possibility to achieve more than
one regime of stationary nonlinear vibrations and how to detect them via the
associated dc Josephson currents and we discuss possible applications of such a
multistable nanoelectromechanical dynamics.Comment: 4 pages, 5 figure
Generation of tunable Terahertz out-of-plane radiation using Josephson vortices in modulated layered superconductors
We show that a moving Josephson vortex in spatially modulated layered
superconductors generates out-of-plane THz radiation. Remarkably, the magnetic
and in-plane electric fields radiated are of the same order, which is very
unusual for any good-conducting medium. Therefore, the out-of-plane radiation
can be emitted to the vacuum without the standard impedance mismatch problem.
Thus, the proposed design can be more efficient for tunable THz emitters than
previous proposals, for radiation only propagating along the ab-plane.Comment: 7 pages, 1 figure. Phys. Rev. B (2005), in pres
Symmetry breaking induced by random fluctuations for Bose-Einstein condensates in a double-well trap
This paper is devoted to the study of the dynamics of two weakly-coupled
Bose-Einstein condensates confined in a double-well trap and perturbed by
random external forces. Energy diffusion due to random forcing allows the
system to visit symmetry-breaking states when the number of atoms exceeds a
threshold value. The energy distribution evolves to a stationary distribution
which depends on the initial state of the condensate only through the total
number of atoms. This loss of memory of the initial conditions allows a simple
and complete description of the stationary dynamics of the condensate which
randomly visits symmetric and symmetry-breaking states.Comment: 12 pages, 6 figure
Analytic continuation of the Hurwitz Zeta Function with physical application
A new formula relating the analytic continuation of the Hurwitz zeta function
to the Euler gamma function and a polylogarithmic function is presented. In
particular, the values of the first derivative of the real part of the analytic
continuation of the Hurwitz zeta function for even negative integers and the
imaginary one for odd negative integers are explicitly given. The result can be
of interest both on mathematical and physical side, because we are able to
apply our new formulas in the context of the Spectral Zeta Function
regularization, computing the exact pair production rate per space-time unit of
massive Dirac particles interacting with a purely electric background field.Comment: Replaced version, minor changes. 9 pages, to be published in J. Math.
Phy
Observation of mesoscopic conductance fluctuations in YBaCuO grain boundary Josephson Junctions
Magneto-fluctuations of the normal resistance R_N have been reproducibly
observed in high critical temp erature superconductor (HTS) grain boundary
junctions, at low temperatures. We attribute them to mesoscopic transport in
narrow channels across the grain boundary line. The Thouless energy appears to
be the relevant energy scale. Our findings have significant implications on
quasiparticle relaxation and coherent transport in HTS grain boundaries.Comment: Revised version, minor changes. 4 pages, 4 figure
- …