arXiv subjects

Bin Liu

Publications and source records attributed to Bin Liu.

587 records · Page 33Linked to original sources

arXiv2007

Role of Particle Interactions in the Feshbach Conversion of Fermion Atoms to Bosonic Molecules

We investigate the Feshbach conversion of fermion atomic pairs to condensed boson molecules with a microscopic model that accounts the repulsive interactions among all the particles involved. We find that the conversion efficiency is enhanced by the interaction between boson molecules while suppressed by the interactions between fermion atoms and between atom and molecule. In certain cases, the combined effect of these interactions leads to a ceiling of less than 100% on the conversion efficiency even in the adiabatic limit. Our model predicts a non-monotonic dependence of the efficiency on mean atomic density. Our theory agrees well with recent experiments on $^6$Li and $^{40}$K.

cond-mat.mes-hall↗

arXiv2007

MEMS-Based Optical Beam Steering System for Quantum Information Processing in 2D Atomic Systems

In order to provide scalability to quantum information processors utilizing trapped atoms or ions as quantum bits (qubits), the capability to address multiple individual qubits in a large array is needed. Micro-electromechanical systems (MEMS) technology can be used to create a flexible and scalable optical system to direct the necessary laser beams to multiple qubit locations. We developed beam steering optics using controllable MEMS mirrors that enable one laser beam to address multiple qubit locations in a 2 dimensional trap lattice. MEMS mirror settling times of 10 us were demonstrated which allow for fast access time between qubits.

physics.atom-ph↗

arXiv2006

Josephson Oscillation and Transition to Self-Trapping for Bose-Einstein-Condensates in a Triple-Well Trap

We investigate the tunnelling dynamics of Bose-Einstein-Condensates(BECs) in a symmetric as well as in a tilted triple-well trap within the framework of mean-field treatment. The eigenenergies as the functions of the zero-point energy difference between the tilted wells show a striking entangled star structure when the atomic interaction is large. We then achieve insight into the oscillation solutions around the corresponding eigenstates and observe several new types of Josephson oscillations. With increasing the atomic interaction, the Josephson-type oscillation is blocked and the self-trapping solution emerges. The condensates are self-trapped either in one well or in two wells but no scaling-law is observed near transition points. In particular, we find that the transition from the Josephson-type oscillation to the self-trapping is accompanied with some irregular regime where tunnelling dynamics is dominated by chaos. The above analysis is facilitated with the help of the Poicaré section method that visualizes the motions of BECs in a reduced phase plane.

cond-mat.other↗

arXiv2006

Heat transport of electron-doped Cobaltates

Within the t-J model, the heat transport of electron-doped cobaltates is studied based on the fermion-spin theory. It is shown that the temperature dependent thermal conductivity is characterized by the low temperature peak located at a finite temperature. The thermal conductivity increases monotonously with increasing temperature at low temperatures T $<$ 0.1$J$, and then decreases with increasing temperature for higher temperatures T $>$ 0.1$J$, in qualitative agreement with experimental result observed from Na$_{x}$CoO$_{2}$ .

cond-mat.str-el↗

arXiv2006

Implicit Density Functional Theory

A fermion ground state energy functional is set up in terms of particle density, relative pair density, and kinetic energy tensor density. It satisfies a minimum principle if constrained by a complete set of compatibility conditions. A partial set, which thereby results in a lower bound energy under minimization, is obtained from the solution of model systems, as well as a small number of exact sum rules. Prototypical application is made to several one-dimensional spinless non-interacting models. The effectiveness of "atomic" constraints on model "molecules" is observed, as well as the structure of systems with only finitely many bound states.

physics.chem-ph↗

arXiv2005

Test of the Stokes-Einstein relation in a two-dimensional Yukawa liquid

The Stokes-Einstein relation, relating the diffusion and viscosity coefficients D and eta, is tested in two dimensions. An equilibrium molecular-dynamics simulation was used with a Yukawa pair potential. Regimes are identified where motion is diffusive and D is meaningful. The Stokes-Einstein relation, D ~ kT, was found to be violated near the disordering transition; under these conditions collective particle motion exhibits dynamical heterogeneity. At slightly higher temperatures, however, the Stokes-Einstein relation is valid. These results may be testable in strongly-coupled dusty plasma experiments.

cond-mat.soft↗

arXiv2005

Kinetic energy driven superconductivity in the electron doped cobaltate Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O

Within the charge-spin separation fermion-spin theory, we have shown that the mechanism of superconductivity in the electron doped cobaltate Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O is ascribed to its kinetic energy. The dressed fermions interact occurring directly through the kinetic energy by exchanging magnetic excitations. This interaction leads to a net attractive force between dressed fermions, then the electron Cooper pairs originating from the dressed fermion pairing state are due to the charge-spin recombination, and their condensation reveals the superconducting ground state. The superconducting transition temperature is identical to the dressed fermion pair transition temperature, and is suppressed to a lower temperature due to the strong magnetic frustration. The optimal superconducting transition temperature occurs in the electron doping concentration $δ\approx 0.29$, and then decreases for both underdoped and overdoped regimes, in qualitative agreement with the experimental results.

cond-mat.str-el↗

arXiv2005

Superconductivity in Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O driven by the kinetic energy

Within the charge-spin separation fermion-spin theory, the mechanism of superconductivity in Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O is studied. It is shown that dressed fermions interact occurring directly through the kinetic energy by exchanging magnetic excitations. This interaction leads to a net attractive force between dressed fermions(then the electron Cooper pairs), and their condensation reveals the superconducting ground state. The optimal superconducting transition temperature occurs in the electron doping concentration $δ\approx 0.29$, and then decreases for both underdoped and overdoped regimes, in qualitative agreement with the experimental results.

cond-mat.supr-con↗

arXiv2005

Shear viscosity of two-dimensional Yukawa systems in liquid state

The shear viscosity of a two-dimensional (2D) liquid was calculated using equilibrium molecular dynamics simulations with a Yukawa potential. The shear viscosity has a minimum, at a Coulomb coupling parameter of about 17, arising from the temperature dependence of the kinetic and potential contributions. Previous calculations of 2D viscosity were less extensive, and for a different potential. The stress autocorrelation function was found to decay rapidly, contrary to some earlier work. These results are useful for 2D condensed matter systems and are compared to a recent dusty plasma experiment.

cond-mat.soft↗

arXiv2004

Charge transport of electron doped Mott insulators on a triangular lattice

The charge transport of electron doped Mott insulators on a triangular lattice is investigated within the t-J model based on the partial charge-spin separation fermion-spin theory. The conductivity spectrum shows a low-energy peak and the unusual midinfrared band, while the resistivity is characterized by a crossover from the high temperature metallic-like to the low temperature insulating-like behavior, in qualitative agreement with experiments. Our results also show that the mechanism that cause this unusual charge transport is closely related with a competition between the kinetic energy and magnetic energy in the system.

cond-mat.str-el↗

arXiv2002

Two-Body Dirac Equations for Nucleon-Nucleon Scattering

We investigate the nucleon-nucleon interaction by using the meson exchange model and the two body Dirac equations of constraint dynamics. This approach to the two body problem has been successfully tested for QED and QCD relativistic bound states. An important question we wish to address is whether or not the two body nucleon-nucleon scattering problem can be reasonably described in this approach as well. This test involves a number of related problems. First we must reduce our two body Dirac equations exactly to a Schroedinger-like equation in such a way that allows us to use techniques to solve our two body Dirac equations already developed for Schroedinger-like systems in nonrelativistic quantum mechanics. Related to this we present a new derivation of Calogero's variable phase shift differential equation for coupled Schroedinger-like equations. Then we determine if the use of nine meson exchanges in our two body Dirac equations give a reasonable fit to the experimental scattering phase shifts for n-p scattering. The data involves seven angular momentum states including both singlet and the triplet spin states with orbital angular momentum 0,1,2. Two models that we have tested give us a fairly good fit. The parameters obtained by fitting the n-p experimental scattering phase shift give a fairly good prediction for most of the p-p experimental scattering phase shifts examined (for the spin singlet S and D states and spin triplet P states). Thus the two body Dirac equations of constraint dynamics presents us with a fit that encourages the exploration of a more realistic model. We outline generalizations of the meson exchange model for invariant potentials that may possibly improve the fit.

nucl-th↗