Botimer and Taborek (2016) measured the mass flux of superfluid $^4$He through a capillary into an evacuated chamber for various temperatures and pressures of the reservoir chamber. They found a sharp transition from low flux at low pressures to high flux at large pressures. Here it is shown that the superfluid condition of chemical potential equality predicts the induced temperature and also the transition pressure, which is attributed to the transition from a semispherical cap to a pool of $^4$He at the exit of the capillary. The results show that the two-fluid equations of superfluid flow, Landau's phonon-roton theory, and Feynman's critical vortex theory are unnecessary for a quantitative account of the measured transition pressure.
We study numerically nonuniform quantum turbulence of coflow in a square channel by the vortex filament model. Coflow means that superfluid velocity $\bm{v}_s$ and normal fluid velocity $\bm{v}_n$ flow in the same direction. Quantum turbulence for thermal counterflow has been long studied theoretically and experimentally. In recent years, experiments of coflow are performed to observe different features from thermal counterflow. By supposing that $\bm{v}_s$ is uniform and $\bm{v}_n$ takes the Hagen-Poiseiulle profile, our simulation finds that quantized vortices are distributed inhomogeneously. Vortices like to accumulate on the surface of a cylinder with $\bm{v}_s \simeq \bm{v}_n$. Consequently, the vortex configuration becomes degenerate from three-dimensional to two-dimensional.
A general discussion of the simulation procedure of the full susceptibility tensor and isothermal magnetization pseudovector for compounds comprising weakly-interacting magnetic centers is presented. A single-crystal-sample as well as a powder-sample case are considered. The procedure is used to obtain explicit expressions for the full susceptibility tensor for spins S=1, 3/2, 2, and 5/2 for non-vanishing rhombic local anisotropy and any form of spectroscopic tensor.
The newly popular topic of "phonon diodes" is discussed in the context of a broader issue of reciprocity in reflection/transmission (R-T) of waves. We first review a theorem well known in electromagnetism and optics but underappreciated in acoustics and phonon physics, stating that the matrix of R-T coefficients for properly normalized amplitudes is symmetric for linear systems that conform to power conservation and time reversibility for wave fields. It is shown that linear structures proposed for "acoustic diodes" in fact do obey R-T reciprocity, and thus should not strictly be called diodes or isolators. We also review examples of nonlinear designs violating reciprocity, and conclude that an efficient acoustic isolator has not yet been demonstrated. Finally, we consider the relationship between acoustic isolators and "thermal diodes", and show that ballistic phonon transport through a linear structure, whether an acoustic diode or not, is unlikely to form the basis for a thermal diode.
It is shown that the limiting transition from the geometrical configuration "plate -plate" to configuration "small particle -plate" being frequently used in the theory of Lifshitz -Pitaevskii, is not continually true. On the other hand, the known solution to the problem in the last configuration can be used to verify the generalizations of the theory being worked out in the former configuration.
We present an introductory overview of the use of spin chains as quantum wires, which has recently developed into a topic of lively interest. The principal motivation is in connecting quantum registers without resorting to optics. A spin chain is a permanently coupled 1D system of spins. When one places a quantum state on one end of it, the state will be dynamically transmitted to the other end with some efficiency if the spins are coupled by an exchange interaction. No external modulations or measurements on the body of the chain, except perhaps at the very ends, is required for this purpose. For the simplest (uniformly coupled) chain and the simplest encoding (single qubit encoding), however, dispersion reduces the quality of transfer. We present a variety of alternatives proposed by various groups to achieve perfect quantum state transfer through spin chains. We conclude with a brief discussion of the various directions in which the topic is developing.
A new scheme to calculate the exchange tensor $\underline{\underline{J}}_{ij}$ describing in a phenomenological way the anisotropic exchange coupling of two moments in a magnetically ordered system is presented. The ab-initio approach is based on spin-polarised relativistic multiple-scattering theory within the framework of spin-density functional theory. The scheme is applied to ferromagnetic CrTe as well as the diluted magnetic semiconductor (DMS) system Ga$_{1-x}$Mn$_{x}$As. In the later case the results show that there is a noticeable anisotropy in the exchange coupling present, although not as pronounced as suggested in recent theoretical investigations.
From an extensive calculation of static properties of a trapped Fermi superfluid at zero temperature using a density-functional formulation, we demonstrate a universal behavior of its observables, such as energy, chemical potential, radius etc., over the crossover from the BCS limit to unitarity leading to scaling over many orders of magnitude in fermion number. This scaling allows to predict the static properties of the system, with a large number ($\sim 10^5$) of fermions, over the crossover with an error of 1-2%, from the knowledge of those for a small number ($\sim 10$) of fermions.
We review the main properties of Spin Waves condensation to a coherent quantum state, named Homogeneously Precessing Domain (HPD). We describe the long range coherent transport of magnetization by Spin Supercurrent in antiferromagnetic superfluid 3He. This quantum phenomenon was discovered 20 years ago. Since then, many magnetic extensions of superconductivity and superfluidity have been observed: spin Josephson phenomena, spin current vortices, spin phase slippage, long distance magnetization transport by spin supercurrents, etc. Several new supercurrent phenomena have been discovered, like magnetically excited coherent quantum states, NMR in the molecular Landau field, spin-current turbulence, formation of stable non-topological solitons etc.
We consider cold polar molecules confined in a helical optical lattice similar to those used in holographic microfabrication. An external electric field polarizes molecules along the axis of the helix. The large-distance inter-molecular dipolar interaction is attractive but the short-scale interaction is repulsive due to geometric constraints and thus prevents collapse. The interaction strength depends on the electric field. We show that a zero-temperature second-order liquid-gas transition occurs at a critical field. It can be observed under experimentally accessible conditions.
We show that dark solitons in 1D bose systems may be excited by resonant absorption of single quanta of an external ac field. The energy of the quantum $\hbarω$ should be slightly blue-detuned from the energy of a soliton with momentum $\hbar q$, where $q$ is the external field wavenumber $q$. We calculate the absorption cross-section and show that it has power-law dependence on the frequency detuning. This reflects the quantum nature of the absorption process and the orthogonality catastrophe phenomenon associated with it.
We map out the phase diagram of a dilute two-component atomic fermion gas with unequal populations and masses under a Feshbach resonance. As in the case of equal masses, no uniform phase is stable for an intermediate coupling regime. For majority component heavier, the unstable region moves towards the BEC side. When the coupling strength is increased from the normal phase, there is an increased parameter space where the transition is into the FFLO state. The converse is true if the majority is light.
A new type of Coulomb gas is defined, consisting of arbitrary numbers of point charges of two species executing Brownian motions under the influence of their mutual electrostatic repulsion. Being a generalization of a model of identical particles introduced by Dyson as a dynamical system describing non-equilibrium state of various random matrix ensembles, our system gives an exact mathematical description of the Brownian motion of charges of magnitudes $ Q_1 $ and $ Q_2 $, such that $ βQ_1 Q_2 = 1 $ on the line or circle, where $β$ is an inverse temperature of the gas.
Phase transitions in the three-dimensional diluted Ising antiferromagnet in an applied magnetic field are analyzed numerically. It is found that random magnetic field in a system with spin concentration below a certain threshold induces a crossover from second-order phase transition to first-order transition to a new phase characterized by a spin-glass ground state and metastable energy states at finite temperatures.
We make an estimate of the possible range of $ΔT_c$ induced by high-pressure effects in post-metallic superconductors by using the theory of {\it extended irreversible/reversible thermodynamics} and Pippard's length scale. The relationship between the increment of the superconducting temperature and the increase of the pressure is parabolic.
Nodal domains are studied both for real $ψ_R$ and imaginary part $ψ_I$ of the wavefunctions of an open microwave cavity and found to show the same behavior as wavefunctions in closed billiards. In addition we investigate the variation of the number of nodal domains and the signed area correlation by changing the global phase $φ_g$ according to $ψ_R+iψ_I=e^{iφ_g}(ψ_R'+iψ_I')$. This variation can be qualitatively, and the correlation quantitatively explained in terms of the phase rigidity characterising the openness of the billiard.
Brownian motors are devices which "rectify" Brownian motion, i.e. they can generate a current of particles out of unbiased fluctuations. Brownian motors are important for the understanding of molecular motors, and are also promising for the realization of new nanolelectronic devices. Among the different systems that can be used to study Brownian motors, cold atoms in optical lattices are quite an unusual one: there is no thermal bath and both the potential and the fluctuations are determined by laser fields. In this article recent experimental implementations of Brownian motors using cold atoms in optical lattices are reviewed.
In a recent paper [PRL 91, 138103 (2003)] a new mechanism to explain the cold denaturation of proteins, based on the loss of local low-density water structure, has been proposed. In the present paper this mechanism is tested by means of full atom numerical simulations. In good agreement with this proposal, cold denaturation resulting in the unfolded state was found at the High Density Liquid (HDL) state of water, at which the amount of open tetragonal hydrogen bonds decreases at cooling.
This letter adresses the challenging problems posed to the Kubo-Anderson (KA) theory by the discovery of intermittent resonant fluorescence with a non-exponential distribution of waiting times. We show how to extend the KA theory from aged to aging systems, aging for a very extended time period or even forever, being a crucial consequence of non-Poisson statistics.