1,721,299 research outputs found
Dynamics of a Bose-Einstein-condensate bright soliton in an expulsive potential
No full textWe theoretically investigate the dynamics of a matter-wave soliton created in a harmonic potential, which is attractive in the transverse direction but expulsive in the longitudinal direction. This Bose-Einstein-condensate (BEC) bright soliton made of 7Li atoms has been observed in a recent experiment [ Khaykovich et al. Science 296 1290 (2002)]. We show that the nonpolynomial Schrödinger equation, an effective one-dimensional equation we derived from the three-dimensional Gross-Pitaevskii equation, is able to reproduce the main experimental features of this BEC soliton in an expulsive potential
Condensate fraction of a two-dimensional attractive Fermi gas
No full textWe investigate the Bose-Einstein condensation of fermionic pairs in a two-dimensional uniform two-component Fermi superfluid obtaining an explicit formula for the condensate density as a function of the chemical potential and the energy gap. By using the mean-field extended Bardeen-Cooper-Schrieffer theory, we analyze, as a function of the bound-state energy, the off-diagonal long-range order in the crossover from the Bardeen-Cooper-Schrieffer state of weakly bound Cooper pairs to the Bose-Einstein condensate of strongly-bound molecular dimers
Three-component Fermi gas withSU(3) symmetry: BCS–BEC crossover in three and two dimensions
No full textWe analyze the crossover from the Bardeen-Cooper-Schrieffer (BCS) state of weakly bound Fermi pairs to the Bose-Einstein condensate (BEC) of molecular dimers for a Fermi gas made of neutral atoms in three hyperfine states with an SU(3) invariant attractive interaction. By solving the extended BCS equations for the total number of particles and the pairing gap, we calculate at zero temperature the pairing gap, the population imbalance, the condensate fraction and the first sound velocity of the uniform system as a function of the interaction strength in both three and two dimensions. In contrast to what is found for the three-dimensional case, in two dimensions the condensate fraction approaches the value 1 only for an extremely large interaction strength and, moreover, the sound velocity gives a clear signature of the disappearance of one of the three hyperfine components
Critical temperature of an interacting Bose gas in a generic power-law potential
No full textWe investigate the critical temperature of an interacting Bose gas confined in a trap described by a generic isotropic power-law potential. We compare the results with respect to the non-interacting case. In particular, we derive an analytical formula for the shift of the critical temperature holding to first order in the scattering length. We show that this shift scales as Nn/3(n+2), where N is the number of Bosons and n is the exponent of the power-law potential. Moreover, the sign of the shift critically depends on the power-law exponent n. Finally, we find that the shift of the critical temperature due to finite-size effects vanishes as (N-2n/3(n+2))
Self-trapping, quantum tunneling, and decay rates for a Bose gas with attractive nonlocal interaction
No full textWe study the Bose-Einstein condensation for a cloud of 7Li atoms with attractive nonlocal (finite-range) interaction in a harmonic trap. In addition to the low-density metastable branch, which is present also in the case of local interaction, a new stable branch appears at higher densities. For a large number of atoms, the size of the cloud in the stable high-density branch is independent of the trap size and the atoms are in a macroscopic quantum self-trapped configuration. We analyze the macroscopic quantum tunneling between the low-density metastable branch and the high-density one by using the instanton technique. Moreover, we consider the decay rate of the Bose condensate due to inelastic two- and three-body collisions
Condensate fraction in neutron matter
No full textWe study the Bose-Einstein condensation of fermionic pairs in the uniform neutron matter by using the concept of the off-diagonal long-range order of the two-body density matrix of the system. We derive explicit formulas for the condensate density ρcon and the condensate fraction ρcon/ρ in terms of the scaled pairing energy gap Δ/εF where εF is the Fermi energy. We calculate the condensate fraction ρcon/ρ as a function of the density ρ by using previously obtained results for the pairing gap Δ. We find the maximum condensate fraction (ρcon/ρ)max=0.42 at the density ρ=5.3×10−4 fm−3, which corresponds to the Fermi wave number kF=0.25 fm−1
Reliable Equation of State for Composite Bosons in the 2D BCS-BEC Crossover
No full textWe briefly discuss recent experiments on the BCS-BEC crossover with ultracold alkali-metal atoms both in three-dimensional configurations and two-dimensional ones. Then we analyze the quantum-field-theory formalism used to describe an attractive D-dimensional Fermi gas taking into account Gaussian fluctuations. Finally, we apply this formalism to obtain a reliable equation of state of the 2D system at low temperaratures in the BEC regime of the crossover by performing a meaningful dimensional regularization of the divergent zero-point energy of collective bosonic excitations
From narrow to broad Feshbach resonances: Condensate fraction of Cooper pairs and preformed molecules
No full textWe extend our previous investigations of fermionic condensation in broad Feshbach resonances by using the two-channel model developed for narrow Feshbach resonances. We investigate two crossovers: the Bardeen-Cooper-Schrieffer–Bose-Einstein condensation (BCS-BEC) crossover by changing the s-wave scattering length and the crossover from a narrow to a broad resonance by changing the atom-molecule coupling. At zero temperature we analyze, as a function of both atom-molecule coupling and s-wave scattering length, the chemical potential, the energy gap, and the condensate fraction of atoms. In particular, we predict the contribution of Cooper pairs and preformed molecules to the total condensate density along the two crossovers
- …
