Binary fluid amplifier solves stability and load problems

Digital fluid amplifier has load intensity, high stability, and operates at low reynolds numbers. It contains specially designed nozzles to provide uniform exit-velocity profiles and to ensure jets of low turbulence

The Trapped Polarized Fermi Gas at Unitarity

We consider population-imbalanced two-component Fermi gases under external harmonic confinement interacting through short-range two-body potentials with diverging s-wave scattering length. Using the fixed-node diffusion Monte Carlo method, the energies of the "normal state" are determined as functions of the population-imbalance and the number of particles. The energies of the trapped system follow, to a good approximation, a universal curve even for fairly small systems. A simple parameterization of the universal curve is presented and related to the equation of state of the bulk system.Comment: 4 pages, 2 tables, 2 figure

Superfluid phases of triplet pairing and neutrino emission from neutron stars

Neutrino energy losses through neutral weak currents in the triplet-spin superfluid neutron liquid are studied for the case of condensate involving several magnetic quantum numbers. Low-energy excitations of the multicomponent condensate in the timelike domain of the energy and momentum are analyzed. Along with the well-known excitations in the form of broken Cooper pairs, the theoretical analysis predicts the existence of collective waves of spin density at very low energy. Because of a rather small excitation energy of spin waves, their decay leads to a substantial neutrino emission at the lowest temperatures, when all other mechanisms of neutrino energy loss are killed by a superfluidity. Neutrino energy losses caused by the pair recombination and spin-wave decays are examined in all of the multicomponent phases that might represent the ground state of the condensate, according to modern theories, and for the case when a phase transition occurs in the condensate at some temperature. Our estimate predicts a sharp increase in the neutrino energy losses followed by a decrease, along with a decrease in the temperature, that takes place more rapidly than it would without the phase transition. We demonstrate the important role of the neutrino radiation caused by the decay of spin waves in the cooling of neutron stars.Comment: 24 pages, 5 figure

Zero sound in triplet-correlated superfluid neutron matter

The linear response of a superfluid neutron liquid onto external vector field is studied for the case of ^{3}P_{2}-\,^{3}F_{2} pairing. The consideration is limited to the case when the wave-length of the perturbation is large as compared to the coherence length in the superfluid matter and the transferred energy is small in comparison with the gap amplitude. The obtained results are used to analyse the collisionless phonon-like excitations of the condensate of superfluid neutrons. In particular, we analyze the case of neutron condensation into the state with $m_{j}=0$ which is conventionally considered as the preferable one in the bulk matter of neutron stars. Zero sound (if it exists) is found to be anisotropic and undergoes strong decrement below some temperature threshold depending substantially on the intensity of Fermi-liquid interactions.Comment: 16 pages, 2 figure

Signature of the electron-electron interaction in the magnetic field dependence of nonlinear I-V characteristics in mesoscopic systems

We show that the nonlinear I-V characteristics of mesoscopic samples with metallic conductivity should contain parts which are linear in the magnetic field and quadratic in the electric field. These contributions to the current are entirely due to the electron-electron interaction and consequently they are proportional to the electron-electron interaction constant. We also note that both the amplitude and the sign of the current exhibit random oscillations as a function of temperature

Theory of quantum paraelectrics and the metaelectric transition

We present a microscopic model of the quantum paraelectric-ferroelectric phase transition with a focus on the influence of coupled fluctuating phonon modes. These may drive the continuous phase transition first order through a metaelectric transition and furthermore stimulate the emergence of a textured phase that preempts the transition. We discuss two further consequences of fluctuations, firstly for the heat capacity, and secondly we show that the inverse paraelectric susceptibility displays T^2 quantum critical behavior, and can also adopt a characteristic minimum with temperature. Finally, we discuss the observable consequences of our results.Comment: 5 pages, 2 figure

Weak- to strong pinning crossover

Material defects in hard type II superconductors pin the flux lines and thus establish the dissipation-free current transport in the presence of a finite magnetic field. Depending on the density and pinning force of the defects and the vortex density, pinning is either weak-collective or strong. We analyze the weak- to strong pinning crossover of vortex matter in disordered superconductors and discuss the peak effect appearing naturally in this context.Comment: 4 pages, 2 figure

Nonequilibrium quantum phase transition in itinerant electron systems

We study the effect of the voltage bias on the ferromagnetic phase transition in a one-dimensional itinerant electron system. The applied voltage drives the system into a nonequilibrium steady state with a non-zero electric current. The bias changes the universality class of the second order ferromagnetic transition. While the equilibrium transition belongs to the universality class of the uniaxial ferroelectric, we find the mean-field behavior near the nonequilibrium critical point.Comment: Final version as accepted to Phys. Rev. Let

The Amplitude of Non-Equilibrium Quantum Interference in Metallic Mesoscopic Systems

We study the influence of a DC bias voltage V on quantum interference corrections to the measured differential conductance in metallic mesoscopic wires and rings. The amplitude of both universal conductance fluctuations (UCF) and Aharonov-Bohm effect (ABE) is enhanced several times for voltages larger than the Thouless energy. The enhancement persists even in the presence of inelastic electron-electron scattering up to V ~ 1 mV. For larger voltages electron-phonon collisions lead to the amplitude decaying as a power law for the UCF and exponentially for the ABE. We obtain good agreement of the experimental data with a model which takes into account the decrease of the electron phase-coherence length due to electron-electron and electron-phonon scattering.Comment: New title, refined analysis. 7 pages, 3 figures, to be published in Europhysics Letter

Quasiparticle decay rate of Josephson charge qubit oscillations

We analyze the decay of Rabi oscillations in a charge qubit consisting of a Cooper pair box connected to a finite-size superconductor by a Josephson junction. We concentrate on the contribution of quasiparticles in the superconductors to the decay rate. Passing of a quasiparticle through the Josephson junction tunes the qubit away from the charge degeneracy, thus spoiling the Rabi oscillations. We find the temperature dependence of the quasiparticle contribution to the decay rate for open and isolated systems. The former case is realized if a normal-state trap is included in the circuit, or if just one vortex resides in the qubit; the decay rate has an activational temperature dependence with the activation energy equal to the superconducting gap $\Delta$. In a superconducting qubit isolated from the environment, the activation energy equals $2\Delta$ if the number of electrons is even, while for an odd number of electrons the decay rate of an excited qubit state remains finite in the limit of zero temperature. We estimate the decay rate for realistic parameters of a qubit.Comment: 8 pages, 3 figures, final version as published in PRB, minor change