Critical superfluid velocity in a trapped dipolar gas

We investigate the superfluid properties of a dipolar Bose-Einstein condensate (BEC) in a fully three-dimensional trap. Specifically, we calculate a superfluid critical velocity for this system by applying the Landau criterion to its discrete quasiparticle spectrum. We test this critical velocity by direct numerical simulation of condensate depletion as a blue-detuned laser moves through the condensate. In both cases, the presence of the roton in the spectrum serves to lower the critical velocity beyond a critical particle number. Since the shape of the dispersion, and hence the roton minimum, is tunable as a function of particle number, we thereby propose an experiment that can simultaneously measure the Landau critical velocity of a dipolar BEC and demonstrate the presence of the roton in this system.Comment: 5 pages, 4 figures, version accepted to PR

Radial and angular rotons in trapped dipolar gases

We study Bose-Einstein condensates with purely dipolar interactions in oblate (pancake) traps. We find that the condensate always becomes unstable to collapse when the number of particles is sufficiently large. We analyze the instability, and find that it is the trapped-gas analogue of the ``roton-maxon'' instability previously reported for a gas that is unconfined in two dimensions. In addition, we find that under certain circumstances, the condensate wave function attains a biconcave shape, with its maximum density away from the center of the gas. These biconcave condensates become unstable due to azimuthl excitation - an angular roton.Comment: 4 pages, 3 figure

Dynamical pattern formation during growth of a dual-species Bose-Einstein condensate

We simulate the growth of a dual species Bose-Einstein condensate using a Gross-Pitaevskii equation with an additional gain term giving rise to the growth. Such growth occurs during simultaneous evaporative cooling of a mixture of two gases. The ground state of a dual condensate is normally either a miscible mixture, or an immiscible phase with two spatially separated components. In a cigar trap the ground state typically consists of one component in the center, and the other component flanking it. Our simulations show that when the condensates are formed in a cigar trap and the mixture is phase separated, then the final state upon the end of the growth is generally far from the true ground state of the system. Instead it consists of multiple, interleaved bubbles of the two species. Such a pattern was observed recently in an experiment by Wieman's group at JILA, and our simulations are in good qualitative agreement with the experiment. We explain the pattern formation as due to the onset of modulation instability during growth, and study the dependence of the final state pattern on various parameters of the system

Dipolar Bose gases: Many-body versus mean-field description

We characterize zero-temperature dipolar Bose gases under external spherical confinement as a function of the dipole strength using the essentially exact many-body diffusion Monte Carlo (DMC) technique. We show that the DMC energies are reproduced accurately within a mean-field framework if the variation of the s-wave scattering length with the dipole strength is accounted for properly. Our calculations suggest stability diagrams and collapse mechanisms of dipolar Bose gases that differ significantly from those previously proposed in the literature

Dipolar Bose-Einstein condensates with dipole-dependent scattering length

We consider a Bose-Einstein condensate of polar molecules in a harmonic trap, where the effective dipole may be tuned by an external field. We demonstrate that taking into account the dependence of the scattering length on the dipole moment is essential to reproducing the correct energies and for predicting the stability of the condensate. We do this by comparing Gross-Pitaevskii calculations with diffusion Monte Carlo calculations. We find very good agreement between the results obtained by these two approaches once the dipole dependence of the scattering length is taken into account. We also examine the behavior of the condensate in non-isotropic traps

The road to patient experience of care measurement: lessons from the United States

Patient-centered care has become an increasing priority in the United States and plays a prominent role in recent healthcare reforms. One way the country has managed to advance patient-centered care is through establishment of a family of national patient experience surveys (the Consumer Assessment of Healthcare Providers and Systems Plans (CAHPS). CAHPS is publicly reported for several types of providers and was recently tied to hospital reimbursement. This is part of a trend over the last two decades that has shifted provider-patient relationships from a traditional paternal approach to customer service and then to clinical partnership. The health care system in Israel, however, is still struggling to overcome barriers to change in this area. While community based biannual patient experience surveys are conducted by the Myers-JDC-Brookdale Institute, there is no comprehensive national approach to measuring the patient experience across a broad range of settings. Only recently did the Israeli Ministry of Health take its first steps to include patient experience as a dimension of health care quality. In its current position, Israel should learn from the U.S. experience with policies promoting patient-centered care, and specifically the impact on clinical services of measuring the patient experience. Looking at what has happened in the United States, we suggest three main lessons. First, there is a need for a set of national patient experience surveys that would be publicly reported and eventually tied to provider reimbursement. Secondly, the national survey tools should be customized to the unique characteristics of Israeli society and draw from recent research on patient-centeredness to include new and important domains such as patient activation and shared decision-making. Finally, newer technological approaches should be explored with the aim of increasing response rates and the timeliness and usefulness of the surveys