Beam splitting and Hong-Ou-Mandel interference for stored light

Storing and release of a quantum light pulse in a medium of atoms in the tripod configuration are studied. Two complementary sets of control fields are defined, which lead to independent and complete photon release at two stages. The system constitutes a new kind of a flexible beam splitter in which the input and output ports concern photons of the same direction but well separated in time. A new version of Hong-Ou-Mandel interference is discussed.Comment: 8 pages, 3 figure

Persistent currents in a bosonic mixture in the ring geometry

In this paper we analyze the possibility of persistent currents of a two-species bosonic mixture in the one-dimensional ring geometry. We extend the arguments used by Bloch to obtain a criterion for the stability of persistent currents for the two-species system. If the mass ratio of the two species is a rational number, persistent currents can be stable at multiples of a certain total angular momenta. We show that the Bloch criterion can also be viewed as a Landau criterion involving the elementary excitations of the system. Our analysis reveals that persistent currents at higher angular momenta are more stable for the two-species system than previously thought.Comment: 20 pages and 7 figure

Sound Propagation in Elongated Bose-Einstein Condensed Clouds

We consider propagation of sound pulses along the long axis of a Bose-Einstein condensed cloud in a very anisotropic trap. In the linear regime, we demonstrate that the square of the velocity of propagation is given by the square of the local sound velocity, $c^2=nU_0/m$, averaged over the cross section of the cloud. We also carry out calculations in the nonlinear regime, and determine how the speed of the pulse depends on its amplitude.Comment: 4 pages, revtex, 3 eps figure

Bogoliubov sound speed in periodically modulated Bose-Einstein condensates

We study the Bogoliubov excitations of a Bose-condensed gas in an optical lattice. Of primary interest is the long wavelength phonon dispersion for both current-free and current-carrying condensates. We obtain the dispersion relation by carrying out a systematic expansion of the Bogoliubov equations in powers of the phonon wave vector. Our result for the current-carrying case agrees with the one recently obtained by means of a hydrodynamic theory.Comment: 16 pages, no figure

Velocity of sound in a Bose-Einstein condensate in the presence of an optical lattice and transverse confinement

We study the effect of the transverse degrees of freedom on the velocity of sound in a Bose-Einstein condensate immersed in a one-dimensional optical lattice and radially confined by a harmonic trap. We compare the results of full three-dimensional calculations with those of an effective 1D model based on the equation of state of the condensate. The perfect agreement between the two approaches is demonstrated for several optical lattice depths and throughout the full crossover from the 1D mean-field to the Thomas Fermi regime in the radial direction.Comment: final versio

Effects of contractile protein phosphorylation on force development in permeabilized rat cardiac myocytes

The phosphorylation status of myofibrillar proteins influences the Ca2+ responsiveness of the myofilaments,but the contribution of and the interaction between the individual components is poorly characterized. Therefore, in Langendorff perfused rat hearts (n=30), the phosphorylation levels of cardiac myosin binding protein-C (cMyBP-C), troponin I and T (cTnI, cTnT) and myosin light chain 1 and 2 (MLC-1, MLC-2) were determined by 1- and 2-dimensional gel electrophoresis. Isometric force development, its Ca2+-sensitivity, the rate of tension redevelopment (ktr) and passive force (Fpas) were studied at optimal sarcomere length (2.2 μm) in mechanically isolated,permeabilized cardiomyocytes at 15 °C. Protein phosphorylation was varied by: 1) blocking spontaneous cardiac activity by lidocaine (0.35 mM; Quiescence); 2) electrical stimulation of the hearts at 5 Hz (Contraction) and 3. treatment of contracting hearts with Isoprenaline (1 μM). MLC-2 phosphorylation was increased in the Contraction group almost 2-fold, relative to the Quiescence group, whereas cMyBP-C and cTnI phosphorylation remained the same. Isoprenaline resulted in 3.7-fold increases in both cMyBP-C and cTnI phosphorylation, but did not result in a further increase in MLC-2 phosphorylation.No significant differences were found in maximum force and ktr between groups, both before and after protein kinase A (PKA) treatment. Ca2+-sensitivity in the Contraction and Isoprenaline groups was significantly reduced in comparison to the Quiescence group. These differences were largely abolished by PKA and Fpas was reduced. These results highlight the impact of PKA-dependent phosphorylation on Ca2+-sensitivity and provide evidence for an interaction between the effects of TnI and MLC-2 phosphorylation

Solitary waves in clouds of Bose-Einstein condensed atoms

We consider the conditions under which solitary waves can exist in elongated clouds of Bose-Einstein condensed atoms. General expressions are derived for the velocity, characteristic size, and spatial profile of solitary waves, and the low- and high-density limits are examined.Comment: 6 pages, revtex, 1 ps figur

Thomas-Fermi-Dirac-von Weizsacker hydrodynamics in laterally modulated electronic systems

We have studied the collective plasma excitations of a two-dimensional electron gas with an arbitrary lateral charge-density modulation. The dynamics is formulated using a previously developed hydrodynamic theory based on the Thomas-Fermi-Dirac-von Weizsacker approximation. In this approach, both the equilibrium and dynamical properties of the periodically modulated electron gas are treated in a consistent fashion. We pay particular attention to the evolution of the collective excitations as the system undergoes the transition from the ideal two-dimensional limit to the highly-localized one-dimensional limit. We also calculate the power absorption in the long-wavelength limit to illustrate the effect of the modulation on the modes probed by far-infrared (FIR) transmission spectroscopy.Comment: 27 page Revtex file, 15 Postscript figure

Critical velocity in cylindrical Bose-Einstein condensates

We describe a dramatic decrease of the critical velocity in elongated cylindrical Bose-Einstein condensates which originates from the non-uniform character of the radial density profile. We discuss this mechanism with respect to recent measurements at MIT.Comment: 3 pages, 2 eps figures, revised according to referee's comment

Landau damping in trapped Bose-condensed gases

We study Landau damping in dilute Bose-Einstein condensed gases in both spherical and prolate ellipsoidal harmonic traps. We solve the Bogoliubov equations for the mode spectrum in both of these cases, and calculate the damping by summing over transitions between excited quasiparticle states. The results for the spherical case are compared to those obtained in the Hartree-Fock approximation, where the excitations take on a single-particle character, and excellent agreement between the two approaches is found. We have also taken the semiclassical limit of the Hartree-Fock approximation and obtain a novel expression for the Landau damping rate involving the time dependent self-diffusion function of the thermal cloud. As a final approach, we study the decay of a condensate mode by making use of dynamical simulations in which both the condensate and thermal cloud are evolved explicitly as a function of time. A detailed comparison of all these methods over a wide range of sample sizes and trap geometries is presented.Comment: 18 pages, 13 figures, submitted to the New Journal of Physics focus issue on Quantum Gase