arXiv subjects

H. T. C. Stoof

Publications and source records attributed to H. T. C. Stoof.

At least 109 records · Page 6Linked to original sources

arXiv2006

On the Role of Penning Ionization in Photoassociation Spectroscopy

We study the role of Penning ionization on the photoassociation spectra of He(^3S)-He(^3S). The experimental setup is discussed and experimental results for different intensities of the probe laser are shown. For modelling the experimental results we consider coupled-channel calculations of the crossing of the ground state with the excited state at the Condon point. The coupled-channel calculations are first applied to model systems, where we consider two coupled channels without ionization, two coupled channels with ionization, and three coupled channels, for which only one of the excited states is ionizing. Finally, coupled-channel calculations are applied to photoassociation of He(^3S)-He(^3S) and good agreement is obtained between the model and the experimental results.

physics.atom-ph↗

arXiv2006

Dressed-molecules in resonantly-interacting ultracold atomic Fermi gases

We present a detailed analysis of the two-channel atom-molecule effective Hamiltonian for an ultracold two-component homogeneous Fermi gas interacting near a Feshbach resonance. We particularly focus on the two-body and many-body properties of the dressed molecules in such a gas. An exact result for the many-body T-matrix of the two-channel theory is derived by both considering coupled vertex equations and the functional integral methods. The field theory incorporates exactly the two-body physics of the Feshbach scattering by means of simple analytical formulas without any fitting parameters. New interesting many-body effects are discussed in the case of narrow resonances. We give also a description of the BEC-BCS crossover above and below T_C. The effects of different approximations for the selfenergy of the dressed molecules are discussed. The single-channel results are derived as a special limit for broad resonances. Moreover, through an analytic analysis of the BEC limit, the relation between the composite boson of the single-channel model and the dressed-molecule of the two-channel model is established.

cond-mat.other↗

arXiv2006

Vortex-lattice melting in a one-dimensional optical lattice

We investigate quantum fluctuations of a vortex lattice in a one-dimensional optical lattice. Our method gives full access to all the modes of the vortex lattice and we discuss in particular the Bloch bands of the Tkachenko modes. Because of the small number of particles in the pancake Bose-Einstein condensates at every site of the optical lattice, finite-size effects become very important. Therefore, the fluctuations in the vortex positions are inhomogeneous and the melting of the lattice occurs from the outside inwards. Tunneling between neighbouring pancakes substantially reduces the inhomogeneity as well as the size of the fluctuations.

cond-mat.mes-hall↗

arXiv2006

Quasi-condensate growth on an atom chip

We discuss and model an experiment to study quasi-condensate growth on an atom chip. In particular, we consider the addition of a deep dimple to the weak harmonic trap confining an ultracold one-dimensional atomic Bose gas, below or close to the characteristic temperature for quasi-condensate formation. The subsequent dynamics depends critically on both the initial conditions, and the form of the perturbing potential. In general, the dynamics features a combination of shock-wave propagation in the quasi-condensate, and quasi-condensate growth from the surrounding thermal cloud.

cond-mat.stat-mech↗

arXiv2006

Pairing of a trapped resonantly-interacting fermion mixture with unequal spin populations

We consider the phase separation of a trapped atomic mixture of fermions with unequal spin populations near a Feshbach resonance. In particular, we determine the density profile of the two spin states and compare with the recent experiments of Partridge et al. (cond-mat/0511752). Overall we find quite good agreement. We identify the remaining discrepancies and pose them as open problems.

cond-mat.other↗

arXiv2005

Ultracold Superstrings in atomic boson-fermion mixtures

We propose a setup with ultracold atomic gases that can be used to make a nonrelativistic superstring in four spacetime dimensions. In particular, we consider for the creation of the superstring a fermionic atomic gas that is trapped in the core of a vortex in a Bose-Einstein condensate. We explain the required tuning of experimental parameters to achieve supersymmetry between the fermionic atoms and the bosonic modes describing the oscillations in the vortex position. Furthermore, we discuss the experimental consequences of supersymmetry.

cond-mat.other↗

arXiv2005

Feshbach molecules in a one-dimensional Fermi gas

We consider the binding energy and the wave function of Feshbach molecules confined in a one-dimensional matter waveguide. We compare the binding energy with the experiment of Moritz et al. and find excellent agreement for the full magnetic field range explored experimentally.

cond-mat.other↗

arXiv2005

Dressed Feshbach molecules in the BEC-BCS crossover

We present the RPA theory of the BEC-BCS crossover in an atomic Fermi gas near a Feshbach resonance that includes the relevant two-body atomic physics exactly. This allows us to determine the probability $Z$ for the dressed molecules in the Bose-Einstein condensate to be in the closed channel of the Feshbach resonance and to compare with the recent experiments of Partridge {\it et al.} [cond-mat/0505353] with $^{6}$Li. We determine for this extremely broad resonance also the condensate density of the dressed molecules throughout the BEC-BCS crossover.

cond-mat.stat-mech↗

arXiv2005

Feshbach resonances in an optical lattice

We present the theory for ultracold atomic gases in an optical lattice near a Feshbach resonance. In the single-band approximation the theory describes atoms and molecules which can both tunnel through the lattice. Moreover, an avoided crossing between the two-atom and the molecular states occurs at every site. We determine the microscopic parameters of the generalized Hubbard model that describes this physics, using the experimentally known parameters of the Feshbach resonance in the absence of the optical lattice. As an application we also calculate the zero-temperature phase diagram of an atomic Bose gas in an optical lattice.

cond-mat.stat-mech↗

arXiv2005

Quantum phases in a resonantly-interacting Bose-Fermi mixture

We consider a resonantly-interacting Bose-Fermi mixture of $^{40}$K and $^{87}$Rb atoms in an optical lattice. We show that by using a red-detuned optical lattice the mixture can be accurately described by a generalized Hubbard model for $^{40}$K and $^{87}$Rb atoms, and $^{40}$K-$^{87}$Rb molecules. The microscopic parameters of this model are fully determined by the details of the optical lattice and the interspecies Feshbach resonance in the absence of the lattice. We predict a quantum phase transition to occur in this system already at low atomic filling fraction, and present the phase diagram as a function of the temperature and the applied magnetic field.

cond-mat.stat-mech↗

arXiv2004

Sweeping a molecular Bose-Einstein condensate across a Feshbach resonance

We consider the dissociation of a molecular Bose-Einstein condensate during a magnetic-field sweep through a Feshbach resonance that starts on the molecular side of the resonance and ends on the atomic side. In particular, we determine the energy distribution of the atoms produced after the sweep. We find that the shape of the energy distribution strongly depends on the rate of the magnetic-field sweep, in a manner that is in good agreement with recent experiments.

cond-mat.other↗

arXiv2004

Atom-molecule theory of broad Feshbach resonances

We derive the atom-molecule theory for an atomic gas near a broad Feshbach resonance, where the energy dependence of the atom-molecule coupling becomes crucial for understanding experimental results. We show how our many-body theory incorporates the two-atom physics exactly. In particular, we calculate the magnetic moment of a two-component gas of ^{6}Li atoms for a wide range of magnetic fields near the broad Feshbach resonance at about 834 Gauss. We find excellent agreement with the experiment of Jochim et al. [Phys. Rev. Lett. 91, 240402 (2003)].

cond-mat.stat-mech↗

arXiv2004

Vortex-line solitons in a periodically modulated Bose gas

We study the nonlinear excitations of a vortex-line in a Bose-Einstein condensate trapped in a one-dimensional optical lattice. We find that the classical Euler dynamics of the vortex results in a description of the vortex line in terms of a (discrete) one-dimensional Gross-Pitaevskii equation, which allows for both bright and gray soliton solutions. We discuss these solutions in detail and predict that it is possible to create vortex-line solitons with current experimental capabilities.

cond-mat.other↗

arXiv2004

Spontaneous squeezing of a vortex in an optical lattice

We study the equilibrium states of a vortex in a Bose-Einstein condensate in a one-dimensional optical lattice. We find that quantum effects can be important and that it is even possible for the vortex to be strongly squeezed, which reflects itself in a different quantum mechanical uncertainty of the vortex position in two orthogonal directions. The latter is observable by measuring the atomic density after an expansion of the Bose-Einstein condensate in the lattice.

cond-mat.stat-mech↗

arXiv2004

Quantum theory of a vortex line in an optical lattice

We investigate the quantum theory of a vortex line in a stack of weakly-coupled two-dimensional Bose-Einstein condensates, that is created by a one-dimensional optical lattice. We derive the dispersion relation of the Kelvin modes of the vortex line and also study the coupling between the Kelvin modes and the quadrupole modes. We solve the coupled dynamics of the vortex line and the quadrupole modes, both classically as well as quantum mechanically. The quantum mechanical solution reveals the possibility of generating nonequilibrium squeezed vortex states by strongly driving the quadrupole modes.

cond-mat.stat-mech↗

arXiv2004

Inelastic light scattering from a Mott insulator

We propose to use Bragg spectroscopy to measure the excitation spectrum of the Mott insulator state of an atomic Bose gas in an optical lattice. We calculate the structure factor of the Mott insulator taking into account both the selfenergy corrections of the atoms and the corresponding dressing of the atom-photon interaction. We determine the scattering rate of photons in the stimulated Raman transition and show that by measuring this scattering rate in an experiment, in particular the excitation gap of the Mott insulator can be determined.

cond-mat.stat-mech↗

arXiv2004

Crossover temperature of Bose-Einstein condensation in an atomic Fermi gas

We show that in an atomic Fermi gas near a Feshbach resonance the crossover between a Bose-Einstein condensate of diatomic molecules and a Bose-Einstein condensate of Cooper pairs occurs at positive detuning, i.e., when the molecular energy level lies in the two-atom continuum. We determine the crossover temperature as a function of the applied magnetic field and find excellent agreement with the experiment of Regal et al. [Phys. Rev. Lett. 92, 040403 (2004)] that has recently observed this crossover temperature.

cond-mat.stat-mech↗

arXiv2003

Quantum phase transition in an atomic Bose gas with a Feshbach resonance

We show that in an atomic Bose gas near a Feshbach resonance a quantum phase transition occurs between a phase with only a molecular Bose-Einstein condensate and a phase with both an atomic and a molecular Bose-Einstein condensate. We show that the transition is characterized by an Ising order parameter. We also determine the phase diagram of the gas as a function of magnetic field and temperature: the quantum critical point extends into a line of finite temperature Ising transitions.

cond-mat.supr-con↗