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Not Much Since 2001 On Inhomo BEC

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Posted by Richard Ruquist on November 20, 2003 15:38:14 UTC

Here is a list of relevant abstracts from the Cornell archives. Perhaps condensed matter specialists do not publish pre-prints there.

Authors: Zaira Nazario, David I. Santiago
Comments: 4 pages
Subj-class: Soft Condensed Matter
We show that the suppression of light scattering off a Bose Einstein Condensate is equivalent to the Landau argument for superfluidity and thus is a consequence of the {\it Principle of Superfluidity}. The superfluid ground state of a BEC contains nonseparable, nontrivial correlations between the bosons that make up the system, i. e., it is entangled. The correlations in the ground state entangle the bosons into a coherent state for the lowest energy state. The entanglement is so extreme that the bosons that make up the system cannot be excited at long wavenumbers. Their existence at low energies is impossible. Only quantum sound can be excited, i.e. the excitations are Bogolyubov quasiparticles which do not resemble free bosons whatsoever at low energies. This means that the system is superfluid by the Landau argument and the superfluidity is ultimately the reason for suppressed scattering at low wavelengths.
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Modified dynamics of weakly coupled BEC's Josephson Junction (BJJ)
Authors: Yu-ping Huang, Zhen-sheng Yuan, Lin-fan Zhu, Lin-jiao Luo, Xiao-jing Liu, Ke-zun Xu
Comments: 5 pages, 3 figures, submitted to Phys. Rev. A
Subj-class: Soft Condensed Matter
The tunnelling quantum dynamics of bimodal BJJ system is modified through introducing an equilibrium condition, which is based on the assumption that the BJJ is tend to keep on its ground state (with a lowest energy) during the oscillation. The tunnelling dynamics of BJJ with symmetric and asymmetric traps is discussed through numerically solving the modified equations. Stationary states are found to exist in the both BJJs. Compared to previous works, the macroscopic quantum self trapping (MQST) is auto-avoided. Meanwhile, it is revealed that the BJJ oscillates with its inherent frequency which is only related to the Josephson energy, which has been testified experimentally in other contexts.
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Quantum States of Matter of Simple Bosonic Systems: BEC's, Superfluids and Quantum Solids
Authors: Zaira Nazario, David I. Santiago
Comments: 4 pages, 2 figures
Subj-class: Soft Condensed Matter
The phase diagram of a single component Bose system in a lattice at zero temperature is obtained. We calculate the variational energies for the Mott insulating and superfluid phases. Below a certain critical density, which depends monotonically on the well depth of the lattice, the Mott insulating phase is stable over the superfluid phase for low enough tunelling amplitude regardless of whether the number of bosons is or is not incommensurate with the lattice. The transition is discontinuous as the superfluid order parameter jumps from a finite value to zero at the Mott transition.
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BCS and BEC Finally Unified: A Brief Review
Authors: J. Batle, M. Casas, M. Fortes, M. de Llano, O. Rojo, F.J. Sevilla, M.A. Solis, V.V.Tolmachev
Comments: 17 pages including 4 figures. To be published in Cond. Matt. Theories Vol. 18, Ed. Joao da Providencia ((Nova Science Publisher, Inc., N. Y., 200?)
Subj-class: Superconductivity
We review efforts to unify both the Bardeen, Cooper and Schrieffer (BCS) and Bose-Einstein condensation (BEC) pictures of superconductivity. We have finally achieved this in terms of a "\textit{complete} boson-fermion (BF) model" (CBFM) that reduces in special cases to all the main continuum (as opposed to "spin") statistical theories of superconductivity. Our BF model is "complete" in the sense that not only two-electron (2e) but also two-hole (2h) Cooper pairs (CPs) are allowed in arbitrary proportions. In contrast, BCS-Bogoliubov theory--which can also be considered as the theory of a mixture of kinematically independent electrons, 2e- and 2h-CPs--allows only equal, 50%-50%, mixtures of the two kinds of CPs. This is obvious from the perfect symmetry about $\mu$, the electron chemical potential, of the well-known Bogoliubov $v^{2}(\epsilon)$ and $u^{2}(\epsilon)$ coefficients, where $\epsilon$ is the electron energy. The CBFM is then applied to see: a) whether the BCS model interaction for the electron-phonon dynamical mechanism is sufficient to predict the unusually high values of $T_{c}$ (in units of the Fermi temperature) of $\simeq 0.01-0.1$ exhibited by the so-called ``exotic'' superconductors \cite{Brandow} in both 2D and 3D--relative to the low values of $\lesssim 10^{-3}$ more or less correctly predicted by BCS theory for conventional, elemental superconductors; and b) whether it can at least suggest, if not explain, why "hole superconductors" have higher $T_{c}$'s.
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Application to a BEC in an Optical Potential
Authors: Y.B. Band, I. Towers, B. Malomed
Comments: 14 pages, 5 figures
Subj-class: Soft Condensed Matter
We present semiclassical descriptions of Bose-Einstein condensates for configurations with spatial symmetry, e.g., cylindrical symmetry, and without any symmetry. The description of the cylindrical case is quasi-one-dimensional (Q1D), in the sense that one only needs to solve an effective 1D nonlinear Schrodinger equation, but the solution incorporates correct 3D aspects of the problem. The solution in classically allowed regions is matched onto that in classically forbidden regions by a connection formula that properly accounts for the nonlinear mean-field interaction. Special cases for vortex solutions are treated too. Comparisons of the Q1D solution with full 3D and Thomas-Fermi ones are presented.
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Spin-1/2 Collective Excitations in BEC of Interacting Spin-1 Atoms
Authors: Fei Zhou (ITP, Utrecht)
Comments: 5 pages
Subj-class: Statistical Mechanics; Strongly Correlated Electrons
We construct spin-1/2 collective excitations in BEC of interacting spin-1 atoms. These excitations exist in states with a maximal global degeneracy. The stability and energy of these objects are determined by interactions with spin fluctuations and are studied based on a duality relation between hyper-monopoles and magnetic monopoles in physical space.
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Novel Theory for Topological Structure of Vortices in BEC
Authors: Yishi Duan, Xin Liu, Pengming Zhang
Subj-class: Mesoscopic Systems and Quantum Hall Effect
By making use of the $\phi $-mapping topological current theory, a novel expression of $\nabla \times \vec{V}$ in BEC is obtained, which reveals the inner topological structure of vortex lines characterized by Hopf indices and Brouwer degrees. This expression is just that formula Landau and Feynman expected to find out long time ago. In the case of superconductivity, the decomposition theory of U(1) gauge potential in terms of the condensate wave function gives a rigorous proof of London assumption, and shows that each vortex line should carry a quantized flux. The $\phi $-mapping topological current theory of $\nabla \times \vec{V}$ can also gives a precise bifurcation theory of vortex lines in BEC.
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