Two-component Atoms Research Articles

Supersolidity of lattice bosons immersed in strongly correlated Rydberg dressed atoms

Recent experiments have illustrated that long range two-body interactions can be induced by laser coupling atoms to highly excited Rydberg states. Stimulated by this achievement, we study supersolidity of lattice bosons in an experimentally relevant situation. In our setup, we consider two-component atoms on a square lattice, where one species is weakly dressed to an electronically high-lying (Rydberg) state, generating a tunable, soft-core shape long-range interaction. Interactions between atoms of the second species and between the two species are characterized by local inter- and intra-species interactions. Using a dynamical mean-field calculation, we find that interspecies onsite interactions can stabilize a pronounced region of supersolid phases. This is characterized by two distinctive types of supersolids, where the bare species forms supersolid phases that are immersed in strongly correlated quantum phases, i.e. a crystalline solid or supersolid of the dressed atoms. We show that the interspecies interaction leads to a roton-like instability in the bare species and therefore is crucially important to the supersolid formation. We provide a detailed calculation of the interaction potential to show how our results can be explored under current experimental conditions.

Mott transitions in a three-component Falicov-Kimball model: A slave boson mean-field study

Metal-insulator transitions in a three-component Falicov-Kimball model are investigated within the Kotliar-Ruckenstein slave boson mean-field approach. The model describes a mixture of two interacting fermion atom species loaded into an optical lattice at ultralow temperature. One species is two-component atoms, which can hop in the optical lattice, and the other is single-component atoms, which are localized. Different correlation-driven metal-insulator transitions are observed depending on the atom filling conditions and local interactions. These metal-insulator transitions are classified by the band renormalization factors and the double occupancies of the atom species. The filling conditions and the critical value of the local interactions for these metal-insulator transitions are also analytically established. The obtained results not only are in good agreement with the dynamical mean-field theory for the three-component Falicov-Kimball model but also clarify the nature and properties of the metal-insulator transitions in a simple physics picture.

Phase separation of Bose-Einstein condensates of trapped atoms and molecules with a homonuclear Feshbach resonance

We investigate phase separation of Bose-Einstein condensates (BECs) of two-component atoms and one-component molecules with a homonuclear Feshbach resonance. We develop a full model for dilute atomic and molecular gases including correlation of the Feshbach resonance and all kinds of interparticle interactions, and numerically calculate order parameters of the BECs in spherical harmonic oscillator traps at zero temperature with the Bogoliubov's classical field approximation. As a result, we find out that the Feshbach resonance can induce two types of phase separation. The actual phase structures and density profiles of the trapped gases are predicted in the whole parameter region, from the atom dominant regime to the molecule dominant regime. We focus on the role of the molecules in the phase separation. Especially in the atom dominant regime, the role of the molecules is described through effective interactions derived from our model. Furthermore we show that a perturbative and semi-classical limit of our model reproduces the conventional atomic BEC (single-channel) model.

Tunneling dynamics and periodic modulating of a two-component BECs in optical lattices

The tunneling dynamics and periodic modulation effect of a two-component Bose-Einstein condensate in an one-dimensional optical lattice are investigated. By using the two-mode approximation, we study the influence of the interaction between two-component BECs on the tunnelling dynamics of the system numerically. The dynamic behavior of the system is investigated by adding a periodic modulation on the interaction between two-component atoms. We get the region for the onset of the tunneling, unstability and the self-trapping of the system with the changing modulation amplitude and frequency. We find that for the intermediate- and the low- frequency modulations, the dynamic behaviors of the system are dramatically different.

Coupling internal atomic states in a two-component Bose-Einstein condensate via an optical lattice: Extended Mott-state–superfluid transitions

An ultracold gas of coupled two-component atoms in an optical field is studied. Due to the internal two-level structure of the atoms, three competing energy terms exist: atomic kinetic, atomic internal, and atom-atom interaction energies. A novel outcome of this interplay, not present in the regular Bose-Hubbard model, is that in the single band and tight-binding approximations four different phases appear: two superfluid and two Mott phases. When passing through the critical point between the two superfluid or the two Mott phases, a swapping of the internal atomic populations takes place. By means of the strong-coupling expansion, we find the full phase diagram for the four different phases.

Probing spin exchange interaction in two-species bosons in optical lattices by cavity-enhanced light scattering

We study the system that two-component atoms, which are confined in an off-resonance optical lattice, interact with two cavity modes. It has a rich phase diagram composed of many phases, such as anti-ferromagnetic, ferromagnetic, and the XY phases in Mott-insulating (MI) region with odd filling factor. These phases could be distinguished by analyzing the photon numbers with two methods, i.e. the semiclassical approximation and the quantized approach, depending on the intensity of the probe light.

Nonfouling Polymer Brushes via Surface-Initiated, Two-Component Atom Transfer Radical Polymerization

A significant challenge in the field of biomaterials is the nonspecific adsorption of proteins. It has been suggested that overall neutral materials composed of mixed charge components present protein-resistant properties. This work describes the development of a novel nonfouling polymer brush formed from a surface-initiated, two-component atom transfer radical polymerization. The polymer brushes are composed of varying mixtures of positively and negatively charged monomers depending on the polymerization conditions. The polymer brushes were characterized by both atomic force microscopy and electron spectroscopy for chemical analysis to determine the thickness and composition, respectively. The nonspecific adsorption of fibrinogen, lysozyme, and bovine serum albumin was measured using a surface plasmon resonance biosensor. It was found that when the polymer brush surface coating was formed as a statistical copolymer from the two charged components, it had nonfouling properties for all three probe proteins.