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D Blume

Publications and source records attributed to D Blume.

13 recordsLinked to original sources
PubMed2006

Scattering length instability in dipolar Bose-Einstein condensates.

We predict a new kind of instability in a Bose-Einstein condensate composed of dipolar particles. Namely, a comparatively weak dipole moment can produce a large, negative two-body scattering length that can collapse the Bose-Einstein condensate. To verify this effect, we validate mean-field solutions to this problem using exact, diffusion Monte Carlo methods. We show that the diffusion Monte Carlo 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.

Journal Article↗
PubMed2005

Superfluidity of mesoscopic Bose gases under varying confinements.

The superfluid fraction Ns/N of 27 bosons under varying confinement is investigated at finite temperature using well-known properties of the harmonic oscillator and the microscopic path integral Monte Carlo method. We find that Ns/N (i) is essentially independent of the interaction strength for all temperatures considered, (ii) changes profoundly as the effective dimensionality is varied from three to one dimensional, (iii) is approximately equal to the condensate fraction N0/N for spherical Bose gases, and (iv) deviates dramatically from N0/N for highly elongated Bose gases.

Journal Article↗
PubMed2004

Interacting fermions in highly elongated harmonic traps.

Quasi-one-dimensional two-component Fermi gases with effectively attractive and repulsive interactions are characterized for arbitrary interaction strength. The ground-state properties of the gas confined in highly elongated harmonic traps are determined within the local density approximation. For strong attractive effective interactions the existence of a molecular Tonks-Girardeau gas is predicted. The frequency of the lowest breathing mode is calculated as a function of the coupling strength for both attractive and repulsive interactions.

Journal Article↗
PubMed2004

Raman spectroscopy of small para-H2 clusters formed in cryogenic free jets.

Small para-H2 clusters (pH2)N with N=2,...,8 have been identified by Raman spectroscopy in cryogenic free jets of the pure gas, near the Q(0) Raman line of the H2 monomer. The high resolution in space, time, and number size makes it possible to follow their growth kinetics with distance from the orifice. At lower source temperatures liquid clusters appear early in the expansion and then undergo a gradual phase transition to the solid state. The technique is very promising for exploring superfluidity in pure (pH2)N clusters.

Journal Article↗
PubMed2004

Tuning the interactions of spin-polarized fermions using quasi-one-dimensional confinement.

We develop a multichannel scattering theory for atom-atom collisions in quasi-1D geometries. We apply our general framework to the low energy scattering of two spin-polarized fermions and show that tightly confined fermions have infinitely strong interactions at a particular value of the 3D, free-space p-wave scattering volume. Moreover, we describe a mapping of this strongly interacting system of two quasi-1D fermions to a weakly interacting system of two 1D bosons.

Journal Article↗
PubMed2004

Quasi-one-dimensional Bose gases with a large scattering length.

Bose gases confined in highly elongated harmonic traps are investigated over a wide range of interaction strengths using quantum Monte Carlo techniques. We find that the properties of a Bose gas under tight transverse confinement are well reproduced by a 1D model Hamiltonian with contact interactions. We point out the existence of a unitary regime, where the properties of the quasi-1D Bose gas become independent of the actual value of the 3D scattering length a(3D). In this unitary regime, the energy of the system is well described by a hard-rod equation of state. We investigate the stability of quasi-1D Bose gases with positive and negative a(3D).

Journal Article↗
PubMed2002

Formation of atomic tritium clusters and bose-einstein condensates.

We present an extensive study of the static and dynamic properties of systems of spin-polarized tritium atoms. In particular, we calculate the two-body |F,m(F)>=|0,0> s-wave scattering length and show that it can be manipulated via a Feshbach resonance at a field strength of about 870 G. Such a resonance might be exploited to make and control a Bose-Einstein condensate of tritium in the |0,0> state. It is further shown that the quartet tritium trimer is the only bound hydrogen isotope and that its single vibrational bound state is a Borromean state. The ground state properties of larger spin-polarized tritium clusters are also presented and compared with those of helium clusters.

Journal Article↗
PubMed1991

Pulmonary nodule: evaluation with spiral volumetric CT.

Spiral volumetric computed tomography (CT) was used prospectively in 20 patients with a suspected solitary pulmonary nodule less than 1 cm in diameter on plain chest radiographs. Four additional nodules were detected with spiral CT than were detected with conventional CT. This technique required a 12-second breath hold; patient cooperation was excellent.

Humans↗