The eclipsing post-common envelope binary CSS21055: a white dwarf with a probable brown-dwarf companion

We report photometric observations of the eclipsing close binary CSS21055 (SDSS J141126+200911) that strongly suggest that the companion to the carbon-oxygen white dwarf is a brown dwarf with a mass between 0.030 and 0.074 Msun. The measured orbital period is 121.73min and the totality of the eclipse lasts 125s. If confirmed, CSS21055 would be the first detached eclipsing WD+BD binary. Spectroscopy in the eclipse could provide information about the companion's evolutionary state and atmospheric structure.Comment: 6 pages, 5 figure

Quantum whistling in superfluid 4He

Fundamental considerations predict that macroscopic quantum systems such as superfluids and the electrons in superconductors will exhibit oscillatory motion when pushed through a small constriction. Here we report the observation of these oscillations between two reservoirs of superfluid 4He partitioned by an array of nanometer-sized apertures. They obey the Josephson frequency equation and are coherent amongst all the apertures. This discovery at the relatively high temperature of 2K (2000 times higher than related phenomena in 3He) may pave the way for a new class of practical rotation sensors of unprecedented precision.Comment: 6 pages, 3 figures, to be published in Natur

Stationary Josephson effect in a weak-link between nonunitary triplet superconductors

A stationary Josephson effect in a weak-link between misorientated nonunitary triplet superconductors is investigated theoretically. The non-self-consistent quasiclassical Eilenberger equation for this system has been solved analytically. As an application of this analytical calculation, the current-phase diagrams are plotted for the junction between two nonunitary bipolar $f-$wave superconducting banks. A spontaneous current parallel to the interface between superconductors has been observed. Also, the effect of misorientation between crystals on the Josephson and spontaneous currents is studied. Such experimental investigations of the current-phase diagrams can be used to test the pairing symmetry in the above-mentioned superconductors.Comment: 6 pages and 6 figure

Pinhole calculations of the Josephson effect in 3He-B

We study theoretically the dc Josephson effect between two volumes of superfluid 3He-B. We first discuss how the calculation of the current-phase relationships is divided into a mesoscopic and a macroscopic problem. We then analyze mass and spin currents and the symmetry of weak links. In quantitative calculations the weak link is assumed to be a pinhole, whose size is small in comparison to the coherence length. We derive a quasiclassical expression for the coupling energy of a pinhole, allowing also for scattering in the hole. Using a selfconsistent order parameter near a wall, we calculate the current-phase relationships in several cases. In the isotextural case, the current-phase relations are plotted assuming a constant spin-orbit texture. In the opposite anisotextural case the texture changes as a function of the phase difference. For that we have to consider the stiffness of the macroscopic texture, and we also calculate some surface interaction parameters. We analyze the experiments by Marchenkov et al. We find that the observed pi states and bistability hardly can be explained with the isotextural pinhole model, but a good quantitative agreement is achieved with the anisotextural model.Comment: 20 pages, 21 figures, revtex

Josephson effects in dilute Bose-Einstein condensates

We propose an experiment that would demonstrate the ``dc'' and ``ac'' Josephson effects in two weakly linked Bose-Einstein condensates. We consider a time-dependent barrier, moving adiabatically across the trapping potential. The phase dynamics are governed by a ``driven-pendulum'' equation, as in current-driven superconducting Josephson junctions. At a critical velocity of the barrier (proportional to the critical tunneling current), there is a sharp transition between the ``dc'' and ``ac'' regimes. The signature is a sudden jump of a large fraction of the relative condensate population. Analytical predictions are compared with a full numerical solution of the time dependent Gross-Pitaevskii equation, in an experimentally realistic situation.Comment: 4 pages, 1 figur

Josephson Effect between Condensates with Different Internal Structures

A general formula for Josephson current in a wide class of hybrid junctions between different internal structures is derived on the basis of the Andreev picture. The formula extends existing formulae and also enables us to analyze novel B-phase/A-phase/B-phase (BAB) junctions in superfluid helium three systems, which are accessible to experiments. It is predicted that BAB junctions will exhibit two types of current-phase relations associated with different internal symmetries. A ``pseudo-magnetic interface effect'' inherent in the system is also revealed.Comment: 4 pages, 2 figure

Observation of metastable states in spinor Bose-Einstein condensates

Bose-Einstein condensates have been prepared in long-lived metastable excited states. Two complementary types of metastable states were observed. The first is due to the immiscibility of multiple components in the condensate, and the second to local suppression of spin-relaxation collisions. Relaxation via re-condensation of non-condensed atoms, spin relaxation, and quantum tunneling was observed. These experiments were done with F=1 spinor Bose-Einstein condensates of sodium confined in an optical dipole trap.Comment: 3 figures included in paper, fourth figure separat

The quest for companions to post-common envelope binaries: I. Searching a sample of stars from the CSS and SDSS

As part of an ongoing collaboration between student groups at high schools and professional astronomers, we have searched for the presence of circum-binary planets in a bona-fide unbiased sample of twelve post-common envelope binaries (PCEBs) from the Catalina Sky Survey (CSS) and the Sloan Digital Sky Survey (SDSS). Although the present ephemerides are significantly more accurate than previous ones, we find no clear evidence for orbital period variations between 2005 and 2011 or during the 2011 observing season. The sparse long-term coverage still permits O-C variations with a period of years and an amplitude of tens of seconds, as found in other systems. Our observations provide the basis for future inferences about the frequency with which planet-sized or brown-dwarf companions have either formed in these evolved systems or survived the common envelope (CE) phase.Comment: accepted by A&

Measurements of Relative Phase in Binary Mixtures of Bose-Einstein Condensates

We have measured the relative phase of two Bose-Einstein condensates (BEC) using a time-domain separated-oscillatory-field condensate interferometer. A single two-photon coupling pulse prepares the double condensate system with a well-defined relative phase; at a later time, a second pulse reads out the phase difference accumulated between the two condensates. We find that the accumulated phase difference reproduces from realization to realization of the experiment, even after the individual components have spatially separated and their relative center-of-mass motion has damped.Comment: 12 pages, 3 figure