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Feshbach Resonance and Growth of a Bose-Einstein Condensate  [PDF]
C. Yuce,A. Kilic
Physics , 2006, DOI: 10.1103/PhysRevA.74.033609
Abstract: Gross-Pitaevskii equation with gain is used to model Bose Einstein condensation (BEC) fed by the surrounding thermal cloud. It is shown that the number of atoms continuously injected into BEC from the reservoir can be controlled by applying the external magnetic field via Feshbach resonance.
Bose-Einstein Condensation of Erbium  [PDF]
K. Aikawa,A. Frisch,M. Mark,S. Baier,A. Rietzler,R. Grimm,F. Ferlaino
Physics , 2012, DOI: 10.1103/PhysRevLett.108.210401
Abstract: We report on the achievement of Bose-Einstein condensation of erbium atoms and on the observation of magnetic Feshbach resonances at low magnetic field. By means of evaporative cooling in an optical dipole trap, we produce pure condensates of $^{168}$Er, containing up to $7 \times 10^{4}$ atoms. Feshbach spectroscopy reveals an extraordinary rich loss spectrum with six loss resonances already in a narrow magnetic-field range up to 3 G. Finally, we demonstrate the application of a low-field Feshbach resonance to produce a tunable dipolar Bose-Einstein condensate and we observe its characteristic d-wave collapse.
All-optical production of 7Li Bose-Einstein condensation using Feshbach resonances  [PDF]
Noam Gross,Lev Khaykovich
Physics , 2007, DOI: 10.1103/PhysRevA.77.023604
Abstract: We show an all-optical method of making 7Li condensate using tunability of the scattering length in the proximity of a Feshbach resonance. We report the observation of two new Feshbach resonances on |F = 1;mF = 0> state. The narrow (broad) resonance of 7 G (34 G) width is detected at 831 +- 4 G (884 +4 -13 G). Position of the scattering length zero crossing between the resonances is found at 836 +- 4 G. The broad resonance is shown to be favorable for run away evaporation which we perform in a crossed-beam optical dipole trap. Starting directly form the phase space density of a magneto-optical trap we observe a Bose-Einstein condensation threshold in less than 3 s of forced evaporation.
Strongly enhanced inelastic collisions in a Bose-Einstein condensate near Feshbach resonances  [PDF]
J. Stenger,S. Inouye,M. R. Andrews,H. -J. Miesner,D. M. Stamper-Kurn,W. Ketterle
Physics , 1999, DOI: 10.1103/PhysRevLett.82.2422
Abstract: The properties of Bose-Einstein condensed gases can be strongly altered by tuning the external magnetic field near a Feshbach resonance. Feshbach resonances affect elastic collisions and lead to the observed modification of the scattering length. However, as we report here, this is accompanied by a strong increase in the rate of inelastic collisions. The observed three-body loss rate in a sodium Bose-Einstein condensation increased when the scattering length was tuned to both larger or smaller values than the off-resonant value. This observation and the maximum measured increase of the loss rate by several orders of magnitude are not accounted for by theoretical treatments. The strong losses impose severe limitations for using Feshbach resonances to tune the properties of Bose-Einstein condensates. A new Feshbach resonance in sodium at 1195 G was observed.
Observation of Bose-Einstein Condensation of Molecules  [PDF]
M. W. Zwierlein,C. A. Stan,C. H. Schunck,S. M. F. Raupach,S. Gupta,Z. Hadzibabic,W. Ketterle
Physics , 2003, DOI: 10.1103/PhysRevLett.91.250401
Abstract: We have observed Bose-Einstein condensation of molecules. When a spin mixture of fermionic Li-6 atoms was evaporatively cooled in an optical dipole trap near a Feshbach resonance, the atomic gas was converted into Li_2 molecules. Below 600 nK, a Bose-Einstein condensate of up to 900,000 molecules was identified by the sudden onset of a bimodal density distribution. This condensate realizes the limit of tightly bound fermion pairs in the crossover between BCS superfluidity and Bose-Einstein condensation.
Phase diagram of a Bose gas near a wide Feshbach resonance  [PDF]
Lan Yin
Physics , 2007, DOI: 10.1103/PhysRevA.77.043630
Abstract: In this paper, we study the phase diagram of a homogeneous Bose gas with a repulsive interaction near a wide Feshbach resonance at zero temperature. The Bose-Einstein-condensation (BEC) state of atoms is a metastable state. When the scattering length $a$ exceeds a critical value depending on the atom density $n$, $na^3>0.035$, the molecular excitation energy is imaginary and the atomic BEC state is dynamically unstable against molecule formation. The BEC state of diatomic molecules has lower energy, where the atomic excitation is gapped and the molecular excitation is gapless. However when the scattering length is above another critical value, $na^3>0.0164$, the molecular BEC state becomes a unstable coherent mixture of atoms and molecules. In both BEC states, the binding energy of diatomic molecules is reduced due to the many-body effect.
Bogoliubov theory of Feshbach molecules in the BEC-BCS crossover  [PDF]
M. W. J. Romans,H. T. C. Stoof
Physics , 2006, DOI: 10.1103/PhysRevA.74.053618
Abstract: We present the Bogoliubov theory for the Bose-Einstein condensation of Feshbach molecules in a balanced Fermi mixture. Because the Bogoliubov theory includes (Gaussian) fluctuations, we can in this manner accurately incorporate both the two-body and many-body aspects of the BEC-BCS crossover that occurs near a Feshbach resonance. We apply the theory in particular to the very broad Feshbach resonance in atomic Li-6 at a magnetic field of B_0 = 834 G and find good agreement with experiments in that case. The BEC-BCS crossover for more narrow Feshbach resonances is also discussed.
Condensation of Pairs of Fermionic Atoms Near a Feshbach Resonance  [PDF]
M. W. Zwierlein,C. A. Stan,C. H. Schunck,S. M. F. Raupach,A. J. Kerman,W. Ketterle
Physics , 2004, DOI: 10.1103/PhysRevLett.92.120403
Abstract: We have observed Bose-Einstein condensation of pairs of fermionic atoms in an ultracold ^6Li gas at magnetic fields above a Feshbach resonance, where no stable ^6Li_2 molecules would exist in vacuum. We accurately determined the position of the resonance to be 822+-3 G. Molecular Bose-Einstein condensates were detected after a fast magnetic field ramp, which transferred pairs of atoms at close distances into bound molecules. Condensate fractions as high as 80% were obtained. The large condensate fractions are interpreted in terms of pre-existing molecules which are quasi-stable even above the two-body Feshbach resonance due to the presence of the degenerate Fermi gas.
Bose-Einstein condensation temperature of a gas of weakly dissociated diatomic molecules  [PDF]
L. M. Jensen,H. M?kel?,C. J. Pethick
Physics , 2006, DOI: 10.1103/PhysRevA.75.033606
Abstract: We consider the properties of a gas of bosonic diatomic molecules in the limit when few of the molecules are dissociated. Taking into account the effects of dissociation and scattering among molecules and atoms, we calculate the dispersion relation for a molecule, and the thermal depletion of the condensate. We calculate the dependence of the Bose-Einstein condensation temperature of a uniform gas on the atom-atom scattering length, and conclude that, for a broad Feshbach resonance, the condensation temperature increases as the molecular state becomes less strongly bound, thereby giving rise to a maximum in the transition temperature in the BEC-BCS crossover. We also argue on general grounds that, for a gas in a harmonic trap and for a narrow Feshbach resonance, the condensation temperature will decrease with increasing scattering length.
Resonance theory of the crossover from Bardeen-Cooper-Schrieffer superfluidity to Bose-Einstein condensation in a dilute Fermi gas  [PDF]
J. N. Milstein,S. J. J. M. F. Kokkelmans,M. J. Holland
Physics , 2002, DOI: 10.1103/PhysRevA.66.043604
Abstract: We present a description of the behavior of a superfluid gas of fermions in the presence of a Feshbach resonance over the complete range of magnetic field detunings. Starting from a resonance Hamiltonian, we exploit a functional method to describe the continuous behavior from Bardeen-Cooper-Schrieffer to Bose-Einstein condensation type superfluidity. Our results show an ability for a resonance system to exhibit a high critical temperature comparable to the Fermi temperature. The results are derived in a manner that is shown to be consistent with the underlying microscopic scattering physics.
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