Quantum Tunneling of a Dipolar Bose-Einstein Condensate in Optical Lattice

We study quantum tunneling of a dipolar Bose-Einstein condensate in optical lattice when the spin system initially is prepared in a squeezed coherent state. It is found that there exists quantum tunneling between lattices l and l ＋ 1, l and l - 1, respectively. In particular, when the optical lattice is infinitely long and the spin excitations are in the long-wavelength limit, quantum tunneling disappears between lattices l and l ＋ 1, and that l and l - 1. Correspondingly, the magnetic soliton appears.     

Tunneling of Spinor Bose-Einstein Condensates in Optical Lattice

In this letter, we have studied the tunneling effects and fluctuations of spinor Bose-Einstein condensates in optical lattice. It is found that there exist tunneling effects and fluctuations between lattices l and l 1, l and l - 1,respectively. In particular, when the optical lattice is infinitely long and the spin excitations are in the long-wavelength limit, tunneling effects disappear between lattices l and l 1, and l and l - 1. In this case the fluctuations are a constant,and the magnetic soliton appears.     

Tunneling of a Dipolar Bose–Einstein Condensate in an Optical Lattice

We have studied the tunneling and fluctuations of a dipolar Bose–Einstein condensate in an optical lattice, it is found that there exist the tunneling and fluctuations between lattices l and l+1, l and l−1, respectively. In particular, when the optical lattice is infinitely long and the spin excitations are in the long-wavelength limit, tunneling effects disappear between lattices l and l+1, and that l and l−1, in this case the fluctuations are a constant, and the magnetic soliton appears.     

Quantum Tunneling of Spinor Bose–Einstein Condensates in an Optical Lattice

We have studied tunneling of spinor Bose–Einstein condensate in an optical lattice. It is found that, when the system being prepared in a squeezed coherent state, there exist the quantum tunneling between lattices l and l+1, l and l−1, respectively. In particular, when the optical lattice is infinitely long and the spin excitations are in the long-wavelength limit, quantum tunneling disappear between lattices l and l+1, and that l and l−1, in this case the magnetic soliton appears.     

双色光晶格势阱中玻色-爱因斯坦凝聚体的Landau-Zener隧穿行为

考虑玻色-爱因斯坦凝聚体局限于周期性的双色光晶格势阱中,研究其中的Bloch能带结构、第一能隙和第二能隙的Landau-Zener隧穿行为.结果表明,随着双色光晶格势阱的主、次晶格相位差从0增加到π,Bloch能带中第一能隙宽度逐渐增加,而第二能隙宽度逐渐减小.同时发现,双色光晶格势阱的主、次晶格深度及其相位差对第一能隙和第二能隙的Landau-Zener隧穿性质有重要的影响.     

Quantum Tunneling of Two-Species Cold Bosonic Atoms in Optical Lattices

In this letter, we have studied quantum tunneling of two-species cold bosonic atoms in an optical lattices. When the optical lattice is not infinitely long and the spin excitations are not in the long-wavelength limit, quantum tunnelings are presented.     

Observation of photon-assisted tunneling in optical lattices

We have observed tunneling suppression and photon-assisted tunneling of Bose-Einstein condensates in an optical lattice subjected to a constant force plus a sinusoidal shaking. For a sufficiently large constant force, the ground energy levels of the lattice are shifted out of resonance and tunneling is suppressed; when the shaking is switched on, the levels are coupled by low-frequency photons and tunneling resumes. Our results agree well with theoretical predictions and demonstrate the usefulness of optical lattices for studying solid-state phenomena.     

Strongly inhibited transport of a degenerate 1D Bose gas in a lattice

We report the observation of strongly damped dipole oscillations of a quantum degenerate 1D atomic Bose gas in a combined harmonic and optical lattice potential. Damping is significant for very shallow axial lattices (0.25 photon recoil energies), and increases dramatically with increasing lattice depth, such that the gas becomes nearly immobile for times an order of magnitude longer than the single-particle tunneling time. Surprisingly, we see no broadening of the atomic quasimomentum distribution after damped motion. Recent theoretical work suggests that quantum fluctuations can strongly damp dipole oscillations of a 1D atomic Bose gas, providing a possible explanation for our observations.     

Effect of quantum fluctuations on the dipolar motion of bose-einstein condensates in optical lattices

We reexamine dipolar motion of condensate atoms in one-dimensional optical lattices and harmonic magnetic traps including quantum fluctuations within the truncated Wigner approximation. In the strong tunneling limit we reproduce the mean field results with a sharp dynamical transition at the critical displacement. When the tunneling is reduced, on the contrary, strong quantum fluctuations lead to finite damping of condensate oscillations even at infinitesimal displacement. We argue that there is a smooth crossover between the chaotic classical transition at finite displacement and the superfluid-to-insulator phase transition at zero displacement. We further analyze the time dependence of the density fluctuations and of the coherence of the condensate and find several nontrivial dynamical effects, which can be observed in the present experimental conditions.     

Magnetism in artificial lattices

We compare magnetism in two artificial lattice structures, a quantum dot array formed in a two-dimensional electron gas and an optical lattice loaded with repulsive, contact-interacting fermionic atoms. When the tunneling between the lattice sites is strong, both lattices are non-magnetic. With reduced tunneling in the tight-binding limit, the shell-filling of the single-site quantum wells combined with Hund's rule determines the magnetism. This leads to a systematic magnetic phase diagram with non-magnetic, ferromagnetic and antiferromagnetic phases.     

Vortex-Peierls states in optical lattices

We show that vortices, induced in cold atom superfluids in optical lattices, may order in a novel vortex-Peierls ground state. In such a state vortices do not form a simple lattice but arrange themselves in clusters, within which the vortices are partially delocalized, tunneling between classically degenerate configurations. We demonstrate that this exotic quantum many-body state is selected by an order-from-disorder mechanism for a special combination of the vortex filling and lattice geometry that has a macroscopic number of classically degenerate ground states.     

Isolated structures in two-dimensional optical superlattice

Overlaying commensurate optical lattices with various configurations called superlattices can lead to exotic lattice topologies and, in turn, a discovery of novel physics. In this study, by overlapping the maxima of lattices, a new isolated structure is created, while the interference of minima can generate various “sublattice” patterns. Three different kinds of primitive lattices are used to demonstrate isolated square, triangular, and hexagonal “sublattice” structures in a two-dimensional optical superlattice, the patterns of which can be manipulated dynamically by tuning the polarization, frequency, and intensity of laser beams. In addition, we propose the method of altering the relative phase to adjust the tunneling amplitudes in “sublattices”. Our configurations provide unique opportunities to study particle entanglement in “lattices” formed by intersecting wells and to implement special quantum logic gates in exotic lattice geometries.     

Reconfigurable 3D photonic lattices by optical induction for optical control of beam propagation

We report on our recent theoretical and experimental studies of three-dimensional (3D) photonic lattice structures which are established in a bulk nonlinear crystal by employing different optical induction techniques. These 3D photonic lattices bring about new opportunities for controlling the flow of light via coupling engineering originated from the lattice modulation along the beam propagation direction. By fine tuning the lattice parameters, we observe a host of unusual behaviors of beam propagation in such reconfigurable 3D lattices, including enhanced discrete diffraction, light tunneling inhibition—better known as coherent destruction of tunneling (CDT), anomalous diffraction, negative refraction, as well as CDT-based image transmission. In addition, we propose and demonstrate a new way of creating 3D ionic-type photonic lattices by controlled Talbot effect.     

Multiband spectroscopy of ultracold fermions: observation of reduced tunneling in attractive Bose-Fermi mixtures

We perform a detailed experimental study of the band excitations and tunneling properties of ultracold fermions in optical lattices. Employing a novel multiband spectroscopy for fermionic atoms, we can measure the full band structure and tunneling energy with high accuracy. In an attractive Bose-Fermi mixture we observe a significant reduction of the fermionic tunneling energy, which depends on the relative atom numbers. We attribute this to an interaction-induced increase of the lattice depth due to the self-trapping of the atoms.     

The diffusion of hydrogen monomers on hole-doped graphitic lattices: over-barrier transition and quantum tunneling

The diffusion of hydrogen and deuterium monomers on hole-doped graphene (a planar graphitic lattice), the outside wall and the inside wall of hole-doped (6, 0) single-walled carbon nanotubes (a curved graphitic lattice) was investigated using density functional theory and density functional perturbation theory. The jump frequencies for the over-barrier transition and phonon-assisted quantum tunneling were calculated by transition state theory and small-polaron theory, respectively. The effects of the local curvature of the surface and the hole doping on the thermodynamic and kinetic properties of a hydrogen monomer on these graphitic lattices are discussed. Our results demonstrate that it is sufficient to judge the diffusional mobility of a hydrogen monomer on graphitic lattices from just the over-barrier transition, no matter how much it is curved and hole doped, while the quantum tunneling can be safely neglected because it is significantly suppressed by the covalent bonding of hydrogen with the graphitic lattice.     

Quantum Tunneling in an Order-Parameter-Preserving Antiferromagnet

We have studied quantum tunneling in an order-parameter-preserving antiferromagnet with the help of Holstein-Primakoff transformation. It is found that, when the system being prepared in a coherent state, there exist the quantum tunneling between lattices k and k+1, k and k−1, respectively. In particular, when the lattice is infinitely long and the spin excitations are in the long-wavelength limit, quantum tunneling disappear between lattices k and k+1, and that k and k−1, in this case the magnetic soliton appears.     

Fractional quantum Hall states of atoms in optical lattices

We describe a method to create fractional quantum Hall states of atoms confined in optical lattices. We show that the dynamics of the atoms in the lattice is analogous to the motion of a charged particle in a magnetic field if an oscillating quadrupole potential is applied together with a periodic modulation of the tunneling between lattice sites. In a suitable parameter regime the ground state in the lattice is of the fractional quantum Hall type, and we show how these states can be reached by melting a Mott-insulator state in a superlattice potential. Finally, we discuss techniques to observe these strongly correlated states.     

Vortex lattices in planar Bose-Einstein condensates with dipolar interactions

In this Letter, we investigate the effects of dipole-dipole interactions on the vortex lattices in fast rotating Bose-Einstein condensates. For single planar condensate, we show that the triangular lattice structure will be unfavorable when the s-wave interaction is attractive and exceeds a critical value. It will first change to a square lattice, and then become more and more flat with the increase of s-wave attraction, until the collapse of the condensate. For an array of coupled planar condensates, we discuss how the dipole-dipole interactions between neighboring condensates compete with quantum tunneling processes, which affects the relative displacement of two neighboring vortex lattices and leads to the loss of phase coherence between different condensates.     

Bose-Einstein Condensates in Optical Lattices with Higher-Order Interactions

The higher-order interactions of Bose-Einstein condensate in multi-dimensional optical lattices are discussed both analytically and numerically.It is demonstrated that the effects of the higher-order atomic interactions on the sound speed and the stabilities of Bloch waves strongly depend on the lattice strength.In the presence of higher-order effects,tighter and high-dimensional lattices are confirmed to be two positive factors for maintaining the system's energetic stability,and the dynamical instability of Bloch waves can take place simultaneously with the energetic instability.In addition,we find that the higher-order interactions exhibit a long-range behavior and the long-lived coherent Bloch oscillations in a tilted optical lattice exist.Our results provide an effective way to probe the higher-order interactions in optical lattices.     

Observation of vortex pinning in Bose-Einstein condensates

We report the observation of vortex pinning in rotating gaseous Bose-Einstein condensates. Vortices are pinned to columnar pinning sites created by a corotating optical lattice superimposed on the rotating Bose-Einstein condensates. We study the effects of two types of optical lattice: triangular and square. In both geometries we see an orientation locking between the vortex and the optical lattices. At sufficient intensity the square optical lattice induces a structural crossover in the vortex lattice.