Nonreciprocal Phonon Laser in an Asymmetric Cavity with an Atomic Ensemble

Phonon lasers, as a novel kind of lasers for generating coherent sound oscillation, has attracted extensive attention. Here, we theoretically propose a nonreciprocal phonon laser in a hybrid optomechanical system, which is composed of an asymmetric Fabry–Pérot cavity, an ensemble of N identical two-level atoms, and a mechanical oscillator. The effective driving amplitude related to driving direction leads to an obvious difference in mechanical gain and threshold power, bringing about a nonrecipr...     

Toward an ion–photon quantum interface in an optical cavity

We demonstrate several building blocks for an ion–photon interface based on a trapped ⁴⁰Ca⁺ ion in an optical cavity. We identify a favorable experimental configuration and measure system parameters, including relative motion of the trapped ion and the resonator mode. A complete spectrum of cavity-assisted Raman transitions between the 4²S_1/2 and 3²D_5/2 manifolds is obtained. On two of these transitions, we generate orthogonally polarized cavity photons, and we demonstrate coherent manipulation of the corresponding pair of atomic states. Possible implementations of atom-photon entanglement and state mapping within the ion-cavity system are discussed.     

Dynamical Localization in an Asymmetric Two-Electron Quantum Dot Molecule by an Alternating-Current Electric Field

We investigate the dynamics of two interacting electrons in an asymmetric double coupled quantum dot under an ac electric field. The numerical results demonstrate that dynamical localization and Rabi oscillation still exist in such a system under the stronger electron correlation. The two electrons can be regarded as a quasiparticle, which move together between two dots similarly to a boson. The dynamics of two electrons in such a quantum system are mainly confined in a Q subspace, which is constructed by two double-occupied states.     

Quantum—Mechanical Simulation of an Atomic Beam Focused by an Optical Standing Wave

Recent experiments have demonstrated that the light pressure force from an optical standing wave (SW) focuses an atomic beajm to sub-micrometre dimensions.We start from a two-dimensional time-dependent Schrodinger equation and reduce in to a one-dimensional equation by a paraxial approximation.We calculate some theoretical limits on the focusing of an atomic beam by an SW optical field.It is found that two parameters,the atomic velocity and the intensity of the laser beam,play an important role in determining the deposition quality.     

Metastable π junction between an s(±)-wave and an s-wave superconductor

We examine a contact between a superconductor whose order parameter changes sign across the Brillioun zone, and an ordinary, uniform-sign superconductor. Within a Ginzburg-Landau-type model, we find that if the barrier between the two superconductors is not too high, the frustration of the Josephson coupling between different portions of the Fermi surface across the contact can lead to surprising consequences. These include time-reversal symmetry breaking at the interface and unusual energy-phase relations with multiple local minima. We propose this mechanism as a possible explanation for the half-integer flux quantum transitions in composite niobium-iron pnictide superconducting loops, which were discovered in recent experiments [C.-T. Chen et al., Nature Phys. 6, 260 (2010).].     

Effect of an intermediate layer on the strength of an ice−substrate interface

The purpose of this investigation is quantitative determination of deformational changes in the ice structure immediately upon displacement under conditions of high hydrostatic pressure by the method of acoustic emission and estimation of the effect of the structure on the ice?substrate adhesive bond strength. The relation between the reciprocal acoustic compliance of ice, the size of mobile elements of its structure, their resonance eigenfrequency, and the density is established. The model is verified. The correlation of the amplitude?frequency spectra of the acoustic emission on the frictional contact with the acoustic spectra of eigenvibrations on glaciers from remote sources is confirmed. The results obtained can be used for distant study of the modes of motion of ice in glaciers.     

Can an electric field induce an antiferroelectric phase out of a ferroelectric phase?

It has been widely accepted that electric fields favor the ferroelectric phase with parallel electric dipoles over the antiferroelectric phase. With detailed measurements in polycrystalline ceramics of Pb(0.99)Nb(0.02[(Zr(0.57)Sn(0.43)(1-y)Ti(y)](0.98)O(3), we demonstrate in this Letter that electric fields can induce an antiferroelectric phase out of a ferroelectric phase, i.e., trigger an apparently unlikely ferroelectric-to-antiferroelectric phase transition. We suggest that it is caused by the volume contraction from the converse piezoelectric effect at the coercive field with a reversed polarity.     

Suszeptibilitätsmessungen an anisotropen Nickeleisen-Schichten

A d. c. field was applied along one of the anisotropy axes of evaporated nickel-iron films with uniaxial anisotropy, and a small a. c. field was applied perpendicular to the d. c. field. The magnetization amplitude parallel to the a. c. field was measured. The dependence of the susceptibility, measured like this, on the d. c. field strength corresponds to the single domain theory only for films with a smallH _c/H_K ratio or for large d. c. fields. The deviations from the single domain theory and the losses occurring can be explained by the ripple structure of the magnetization in polycrystalline films.     

Sheath Structure of an Electronegative Plasma

We investigate the sheath structure of an electronegative plasma at steady state with the assumptions of cold positive ions and hot negative ions. The modified Bohm criterion is obtained with the Sagdeev potential by introducing a modified ion sound velocity. At the same time the electric potential, net space charge and particles densities in the sheath are analysed in several cases of different temperature ratios of electrons to negative ions and different density ratios of negative ions to positive ions.     

Is Dark Energy an illusion?

Much evidence has accumulated that within the context of general relativistic Friedmann-Robertson-Walker (FRW) cosmology there must exist a new, and gravitationally repulsive, substance in the Universe. The effect of this new type of energy density on the expansion of the Universe is to cause its acceleration, and the name that is given to it is ‘Dark Energy’. To say whether or not Dark Energy really exists, however, requires a definite model for the Universe. That is, to be sure of the existence of Dark Energy, and the cosmological acceleration it causes, we must first be sure of the cosmological model we are using to interpret our observations. This is the subject of the present contribution, which will concentrate on the observational status of the Copernican Principle, which is at the heart of the FRW model. In particular, we will outline recent progress that has been made toward answering the question ‘can the observations usually requiring the existence of Dark Energy be accounted for without introducing any new and exotic types of energy density, if we are prepared to give up some of the assumptions of the standard cosmological model?’, or, alternatively, ‘is Dark Energy an illusion?’.     

Imaging an atomic beam using fluorescence

A fluorescence detection scheme is applied to image an atomic beam. Using two laser diodes as the sources of detection light and pumping light respectively, the fluorescence image of the atomic beam is then observed by a commercial CCD-camera, which is corresponding to the atomic state and velocity distribution. The detection scheme has a great utilization in the experiments of cold atoms and atomic optics.     

Solitons in a Heisenberg Spin Chain with an Easy Axis Under an Oscillating Magnetic Field

The Lax pair given for the equations of motion of a continuum-Heisenberg-spin chain of an easy axis in an oscillating magnetic field.Using an inverse scattering transformation we derive soliton solutions for the case of the easy axis.     

Does general relativity allow an observer to view an eternity in a finite time?

I investigate whether there are general relativistic spacetimes that allow an observerµ to collect in a finite time all the data from the worldline of another observer, where the proper length of's worldline is infinite. The existence of these spacetimes has a bearing on certain problems in computation theory. A theorem shows that most standard spacetimes cannot accommodate this scenario. There are however spacetimes which can: anti-de Sitter spacetime is one example.     

Schrodinger Equation for an Open System

We present a Schrodinger (Liouville) type of equation for a quantum open system.It has a correlated part,and various master equations may be its special cases.It also has significant applications for constructing decoherencefree subspace for quantum computation.It is related to the original Schrodinger (Liouville)equation for the total system through a non-unitary similarity transformation.It is unnecessary for its correlated part to be self-adjoint,so there is a complex spectrum for the corresponding Hamiltonian (Liouvillian),which enables the time evolution of states to be asymmetric.This shows just the correlation to produce evolution of world.