arXiv subjects

Yoshihito Kuno

Publications and source records attributed to Yoshihito Kuno.

78 records · Page 5Linked to original sources

arXiv2015

Phase diagrams of Bose-Hubbard model and Haldane-Bose-Hubbard model with complex hopping amplitudes

In this paper, we study Bose-Hubbard models on the square and honeycomb lattices with complex hopping amplitudes, which are feasible by recent experiments of cold atomic gases in optical lattices. To clarify phase diagrams, we use an extended quantum Monte-Carlo simulations (eQMC). For the system on the square lattice, the complex hopping is realized by an artificial magnetic field. We found that vortex-solid states form for certain set of magnetic field, i.e., the magnetic field with the flux quanta per plaquette $f=p/q$, where $p$ and $q$ are co-prime natural numbers. For the system on the honeycomb lattice, we add the next-nearest neighbor complex hopping. The model is a bosonic analog of the Haldane-Hubbard model. By means of the eQMC, we study the model with both weak and strong on-site repulsions. Numerical study shows that the model has a rich phase diagram. We also found that in the system defined on the honeycomb lattice of the cylinder geometry, an interesting edge state appears.

cond-mat.quant-gas↗

arXiv2015

Real time dynamics and proposal for feasible experiments of lattice gauge-Higgs model simulated by cold atoms

Lattice gauge theory has provided a crucial non-perturbative method in studying canonical models in high-energy physics such as quantum chromodynamics. Among other models of lattice gauge theory, the lattice gauge-Higgs model is a quite important one because it describes wide variety of phenomena/models related to the Anderson-Higgs mechanism such as superconductivity, the standard model of particle physics, and inflation process of the early universe. In this paper, we first show that atomic description of the lattice gauge model allows us to explore real time dynamics of the gauge variables by using the Gross-Pitaevskii equations. Numerical simulations of the time development of an electric flux reveal some interesting characteristics of dynamical aspect of the model and determine its phase diagram. Next, to realize a quantum simulator of the U(1) lattice gauge-Higgs model on an optical lattice filled by cold atoms, we propose two feasible methods: (i) Wannier states in the excited bands and (ii) dipolar atoms in a multilayer optical lattice. We pay attentions to respect the constraint of Gauss's law and avoid nonlocal gauge interactions.

cond-mat.quant-gas↗

arXiv2015

Two-component Bose gas trapped by harmonic and annular potentials: Supercurrent, vortex flow and instability of superfluidity by Rabi coupling

In this paper, we study a system of two-component Bose gas in an artificial magnetic field trapped by concentric harmonic and annular potentials, respectively. The system is realized by gases with two-internal states like the hyperfine states of $^{87}$Rb. We are interested in effects of a Rabi oscillation between them. Two-component Bose Hubbard model is introduced to describe the system, and Gross-Pitaevskii equations are used to study the system. We first study the Bose gas system in the annular trap by varying the width of the annulus and strength of the magnetic field, in particular, we focus on the phase slip and superflow. Then we consider the coupled Bose gas system in a magnetic field. In a strong magnetic field, vortices form a Abrikosov triangular lattice in both Bose-Einstein condensates (BECs), and locations of vortices in the BECs correlate with each other by the Rabi coupling. However, as the strength of the Rabi coupling is increased, vortices start to vibrate around their equilibrium locations. As the strength is increased further, vortices in the harmonic trap start to move along the boundaries of the annulus. Finally for a large Rabi coupling, the BECs are destroyed. Based on our findings about the BEC in the annular trap, we discuss the origin of above mentioned phenomena.

cond-mat.quant-gas↗

arXiv2014

Random-field-induced order in bosonic t-J model

In the present paper, we shall study effect of a random quenched external field for spin order and also multiple Bose-Einstein condensation (BEC). This system is realized by the cold atomic gases in an optical lattice. In particular, we are interested in the strong-repulsion region of two-component gases for which the bosonic t-J model is a good effective model. In the bosonic t-J model, a long-range order of the pseudo-spin and also BEC of atoms appear quite naturally as in the fermion t-J model for the high-temperature superconducting materials. Random Raman scattering between two internal states of a single atom plays a role of the random external field, and we study its effects on the pseudo-spin order and the BEC by means of quantum Monte-Carlo simulations. The random external field breaks a continuous U(1) symmetry existing in the original bosonic t-J model and it induces new orders named random-field-induced order (RFIO). We show a phase diagram of the bosonic t-J model with the random external magnetic field and study the robustness of the RFIO states. We also study topological excitations like vortices and domain wall in the RFIO state. Finally we point out the possibility of a quantum bit by the RFIO.

cond-mat.quant-gas↗

arXiv2012

Bosonic t-J Model in a stacked triangular lattice and its phase diagram

In this paper, we study phase diagram of a system of two-component hard-core bosons with nearest-neighbor (NN) pseudo-spin antiferromagnetic (AF) interactions in a stacked triangular lattice. Hamiltonian of the system contains three parameters one of which is the hopping amplitude $t$ between NN sites, and the other two are the NN pseudo-spin exchange interaction $J$ and the one that measures anisotropy of pseudo-spin interactions. We investigate the system by means of the Monte-Carlo simulations and clarify the low-temperature phase diagram. In particular, we are interested in how the competing orders, i.e., AF order and superfluidity, are realized, and also whether supersolid forms as a result of hole doping into the state of the $\sqrt{3}\times \sqrt{3}$ pseudo-spin pattern with the $120^o$ structure.

cond-mat.str-el↗

arXiv2012

Crystal, Superfluids, Supersolid and Hetero-Structure in System of Two-Component Strongly-Correlated Bosons in a Cubic Optical Lattice

In the present paper, we study finite-temperature phase structure of two-component hard-core bosons in a cubic optical lattice. The system that we study in the present paper is an effective model for the Bose-Hubbard model with strong on-site repulsions and is called bosonic t-J model. This model is a bosonic counterpart of the t-J model for the strongly-correlated electron systems like the high-temperature superconducting materials. We study the model by means of path-integral methods and Monte-Carlo simulations. We found that this system has a very rich phase structure including checkerboard-type "insulating" state, superfluid, phase-separated state, inhomogeneous cloudlet state, etc. We are also interested in the possible supersolid phase with both the checkerboard order and superfluidity and found that additional nearest-neighbor inter-species attractive force induces the supersolid state. In the supersolid state, paired superfluid appears in addition to the superfluid of single atom. This result gives important insight into mechanism of the high-temperature superconductivity of the cuprate.

cond-mat.quant-gas↗