Yajiang Hao

Intrinsic relation between ground-state fidelity and the characterization of a quantum phase transition

The electronic structure of the highly ordered alloy Cr3Co with the DO3 structure has been studied by FLAPW calculations. It is found that the ferrimagnetic state is stable and that the equilibrium lattice constant of Cr3Co equals 5.77 angstrom. A large peak in majority spin density of states (DOS) and an energy gap in minority spin DOS are observed at the Fermi level, which results in a high spin polarization of 90% in the ordered alloy Cr3Co. The total magnetic moment of Cr3Co is 3.12 mu(B), which is close to the ideal value of 3 mu(B) derived from the Slater-Pauling curve. An antiparallel alignment between the moments on the Cr (A, C) sites and the Cr (B) sites is observed. Finally, the effect of lattice distortion on the electronic structure and on magnetic properties of Cr3Co compound is studied. A spin polarization higher than 80% can be obtained between 5.55 and 5.90 angstrom. With increasing lattice constant, the magnetic moments on the (A, C) sites increase and the moments on the (B, D) sites decrease. They compensate each other and make the total magnetic moment change only slightly. (c) 2007 Elsevier B.V. All rights reserved.

Ground-state properties of one-dimensional ultracold Bose gases in a hard-wall trap

We investigate the ground state of the system of N bosons enclosed in a hard-wall trap interacting via a repulsive or attractive delta-function potential. Based on the Bethe ansatz method, the explicit ground state wave function is derived and the corresponding Bethe ansatz equations are solved numerically for the full physical regime from the Tonks limit to the strongly attractive limit. It is shown that the solution takes a different form in different regime. We also evaluate the one body density matrix and second-order correlation function of the ground state for finite systems. In the Tonks limit the density profiles display the Fermi-like behavior, while in the strongly attractive limit the Bosons form a bound state of N atoms corresponding to the N-string solution. The density profiles show the continuous crossover behavior in the entire regime. Further, the correlation function indicates that the Bose atoms bunch closer as the interaction constant decreases.

Ground-state properties of hard-core anyons in one-dimensional optical lattices

We investigate the ground-state properties of anyons confined in one-dimensional optical lattices with a weak harmonic trap using the exact numerical method based on Jordan-Wigner transformation. It is shown that in the Bose limit (chi=1) and Fermi limit (chi=0) the momentum distributions are symmetric but in between they are asymmetric. It turns out that the origin of asymmetry comes from the fractional statistics that anyons obey. The occupation distribution and the modulus of natural orbitals show crossover behaviors from the Bose limit to the Fermi limit.

Transition from a Tonks-Girardeau gas to a super-Tonks-Girardeau gas as an exact many-body dynamics problem

We investigate transition of a one-dimensional interacting Bose gas from a strongly repulsive regime to a strongly attractive regime, where a stable highly excited state known as the super Tonks-Girardeau gas was experimentally realized very recently. By solving exact dynamics of the integrable Lieb-Liniger Bose gas, we demonstrate that such an excited gas state can be a very stable dynamic state. Furthermore we calculate the breathing mode of the super Tonks-Girardeau gas which is found to be in good agreement with experimental observation. Our results show that the highly excited super Tonks-Girardeau gas phase can be well understood from the fundamental theory of the solvable Bose gas.

Ground-state properties of a few-boson system in a one-dimensional hard-wall split potential

We carry out a detailed examination of the ground-state properties of a few-boson system in a one-dimensional hard-wall potential with a delta split in the center. In the Tonks-Girardeau limit with infinite repulsion between particles, we use the Bose-Fermi mapping to construct the exact N-particle ground-state wave function, which allows us to study the correlation properties accurately. For the general case with finite interparticle interaction, the exact diagonalization method is exploited to study the ground-state density distribution, occupation number distribution, and momentum distribution for variable interaction strengths and barrier heights. The secondary peaks in the momentum distribution reveal the interference between particles on the two sides of the split, which is more prominent for large barrier strength and small interaction strength.

Density-functional theory of two-component Bose gases in one-dimensional harmonic traps

We investigate the ground-state properties of two-component Bose gases confined in one-dimensional harmonic traps in the scheme of density-functional theory. The density-functional calculations employ a Bethe-ansatz-based local-density approximation for the correlation energy, which accounts for the correlation effect properly from the weakly interacting regime to the strongly interacting regime. For the binary Bose mixture with spin-independent interaction, the homogeneous reference system is exactly solvable by the Bethe-ansatz method. Within the local-density approximation, we determine the density distribution of each component and study its evolution from Bose distributions to Fermi-like distribution with the increase in interaction. For the binary mixture of Tonks-Girardeau gases with a tunable interspecies repulsion, with a generalized Bose-Fermi transformation we show that the Bose mixture can be mapped into a two-component Fermi gas, which corresponds to exact soluble Yang-Gaudin model for the homogeneous system. Based on the ground-state energy function of the Yang-Gaudin model, the ground-state density distributions are calculated for various interspecies interactions. It is shown that with the increase in interspecies interaction, the system exhibits composite-fermionization crossover.

Quantum dynamics of repulsively bound atom pairs in the Bose-Hubbard model

Abstract.We investigate the quantum dynamics of repulsively bound atom pairs in an optical lattice described by the periodic Bose-Hubbard model both analytically and numerically. In the strongly repulsive limit, we analytically study the dynamical problem by the perturbation method with the hopping terms treated as a perturbation. For a finite-size system, we numerically solve the dynamic problem in the whole regime of interaction by the exact diagonalization method. Our results show that the initially prepared atom pairs are dynamically stable and the dissociation of atom pairs is greatly suppressed when the strength of the on-site interaction is much greater than the tunneling amplitude, i.e., the strongly repulsive interaction induces a self-localization phenomenon of the atom pairs.

Quantum entanglement of particles on a ring with fractional statistics

The effect of Ni and Co inserting layers on the quantum well (QW) states of a Cu film grown on Co/Cu(001) is systematically investigated using angle-resolved photoemission spectroscopy. For electron energy E-E(F) < -0.5 eV, we find that both Ni and Co inserting layers behave similarly to serve as a potential-energy barrier to divide the Cu film into two Cu QWs. For energy near the Fermi energy, the Ni and Co inserting layers have different effects on the Cu QW states while the Co thin layer still perturbs the Cu QW states, the Ni inserting layer behaves as if it were a Cu layer, especially at the Fermi energy, even up to 10 ML thickness. Such different effects of the Ni and Co inserting layers are attributed to their different electronic band matching with the Cu energy band. The first-principles calculation confirms that the electron reflectivity near the Fermi level is indeed very different at the Cu/Ni and Cu/Co interfaces, supporting the experimental results.

One-dimensional fermionic gases with attractive p -wave interaction in a hard-wall trap

We investigate the ground state of the one-dimensional fermionic system enclosed in a hard-wall trap with attractive contact p-wave interactions. Based on the Bethe ansatz method, the explicit wave function is derived by numerically solving the Bethe ansatz equations for the full physical regimes (-infinity <= c(F)<= 0). With the exact wave function some quantities which are important in many-body physics are obtained, including the one-body density matrix and the momentum distribution of the ground state for finite system. It is shown that the shell structure of the density profiles disappears with the increase of the interaction and in the fermionic Tonks-Girardeau limit the density distribution shows the same behavior as that of an ideal Bose gas. However, the one-body density matrix and the momentum distribution exhibit completely different structures compared with their bosonic counterparts.

Numerical simulation on tunnel splitting of Bose-Einstein condensate in multi-well potentials

Abstract.The low-energy-level macroscopic wave functions of the Bose-Einstein condensate (BEC) trapped in a symmetric double-well and a periodic potential are obtained by solving the Gross-Pitaevskii equation numerically. The ground state tunnel splitting is evaluated in terms of the even and odd wave functions corresponding to the global ground and excited states respectively. We show that the numerical result is in good agreement with the analytic level splitting obtained by means of the periodic instanton method.