One-dimensional Optical Superlattice Research Articles

Hard-core bosons in a zig-zag optical superlattice

We study a system of hard-core bosons at half-filling in a one-dimensional optical superlattice. The bosons are allowed to hop to nearest and next-nearest neighbor sites producing a zig-zag geometry and we obtain the ground state phase diagram as a function of microscopic parameters using the finite-size density matrix renormalization group (FS-DMRG) method. Depending on the sign of the next-nearest neighbor hopping and the strength of the superlattice potential the system exhibits three different phases, namely the bond-order (BO) solid, the superlattice induced Mott insulator (SLMI) and the superfluid (SF) phase. When the signs of both hopping amplitudes are the same (the "unfrustrated" case), the system undergoes a transition from the SF to the SLMI at a non-zero value of the superlattice potential. On the other hand, when the two amplitudes differ in sign (the "frustrated" case), the SF is unstable to switching on a superlattice potential and also exists only up to a finite value of the next nearest neighbor hopping. This part of the phase diagram is dominated by the BO phase which breaks translation symmetry spontaneously even in the absence of the superlattice potential and can thus be characterized by a bond order parameter. The transition from BO to SLMI appears to be first order.

Magnetic Phases of Fermionic Atoms Confined in 1-D Optical Superlattice

We study the ground state of alkaline-earth fermionic atoms confined in a one-dimensional optical superlattice, when the number of delocalized atoms is one-fourth the number of system sites. We used the density matrix renormalization group method and found a paramagnetic to ferromagnetic quantum phase transition for any value of the potential strength. The local critical antiferromagnetic coupling decreases as the superlattice potential increases.

Topological Mott insulators of ultracold atomic mixtures induced by interactions in one-dimensional optical superlattices

We present exactly solvable examples that topological Mott insulators can emerge from topologically trivial states due to strong interactions between atoms for atomic mixtures trapped in one-dimensional optical superlattice systems. The topological Mott insulating state is characterized by nonzero Chern number and appears in the strongly interacting limit as long as the total band filling factor is an integer, which is not sensitive to the filling of each component. The topological nature of the Mott phase can be revealed by observing the density profile of the trapped system. Our results can be also generalized to the multi-component atomic systems.

Fractional Topological States of Dipolar Fermions in One-Dimensional Optical Superlattices

We study the properties of dipolar fermions trapped in one-dimensional bichromatic optical lattices and show the existence of fractional topological states in the presence of strong dipole-dipole interactions. We find some interesting connections between fractional topological states in one-dimensional superlattices and the fractional quantum Hall states: (i)the one-dimensional fractional topological states for systems at filling factor ν=1/p have p-fold degeneracy, (ii)the quasihole excitations fulfill the same counting rule as that of fractional quantum Hall states, and (iii)the total Chern number of p-fold degenerate states is a nonzero integer. The existence of crystalline order in our system is also consistent with the thin-torus limit of the fractional quantum Hall state on a torus. The possible experimental realization in cold atomic systems offers a new platform for the study of fractional topological phases in one-dimensional superlattice systems.

Ground States of Ultracold Spin-1 Atoms in a Deep Double-Well Optical Superlattice in a Weak Magnetic Field

The ground states of the ultracold spin-1 atoms trapped in a deep one-dimensional double-well optical superlattice in a weak magnetic field are obtained. It is shown that the ground-state diagrams of the reduced double-well model are remarkably different for the antiferromagnetic and ferromagnetic condensates. The transition between the singlet state and nematic state is observed for the antiferromagnetic interaction atoms, which can be realized by modulating the tunneling parameter or the quadratic Zeeman energy. An experiment to distinguish the different spin states is suggested.

Topological Bose-Mott insulators in a one-dimensional optical superlattice.

We study topological properties of the Bose-Hubbard model with repulsive interactions in a one-dimensional optical superlattice. We find that the Mott insulator states of the single-component (two-component) Bose-Hubbard model under fractional fillings are topological insulators characterized by a nonzero charge (or spin) Chern number with nontrivial edge states. For ultracold atomic experiments, we show that the topological Chern number can be detected through measuring the density profiles of the bosonic atoms in a harmonic trap.

Quantum phase transition of alkaline-earth fermionic atoms confined in an optical superlattice

Abstract Using the density matrix renormalization group method, we evaluate the spin and charge gaps of alkaline-earth fermionic atoms in a periodic one-dimensional optical superlattice. The number of delocalized atoms is equal to the lattice size and we consider an antiferromagnetic coupling between delocalized and localized atoms. We found a quantum phase transition from a Kondo insulator spin liquid state without confining potential to a charge-gapped antiferromagnetic state with nonzero potential. For each on-site coupling, there is a critical potential point for which the spin gap vanishes and its value increases linearly with the local interaction.

Multiple quasi-phase-matching in a one-dimensional aperiodically poled optical superlattice

A new method to enhance the output efficiency of the multi-frequency second harmonic generation process has been presented in the one-dimensional aperiodic optical superlattice by sandwiching linear layers between nonlinear media. The linear and nonlinear domain arrangements of aperiodic crystal are designed using the simulated annealing optimization method. The dependence of the output efficiency of second harmonic generation on the linear length has been investigated in detail; the most optimized structure being suggested. A comparison between pure nonlinear and linear–nonlinear layered structures is presented which shows an increasing amount of the output efficiency in the presence of linear layers for the nonlinear aperiodic crystals.

Edge States and Topological Phases in One-Dimensional Optical Superlattices

We show that one-dimensional quasiperiodic optical lattice systems can exhibit edge states and topological phases which are generally believed to appear in two-dimensional systems. When the Fermi energy lies in gaps, the Fermi system on the optical superlattice is a topological insulator characterized by a nonzero topological invariant. The topological nature can be revealed by observing the density profile of a trapped fermion system, which displays plateaus with their positions uniquely determined by the ration of wavelengths of the bichromatic optical lattice. The butterflylike spectrum of the superlattice system can be also determined from the finite-temperature density profiles of the trapped fermion system. This finding opens an alternative avenue to study the topological phases and Hofstadter-like spectrum in one-dimensional optical lattices.

Optical and fast nondestructive identification of the ages of leaded ancient pottery

In this paper, based on the one-dimensional (1D) optical superlattice model, we calculate the average reflectivities (ARs) of leaded ancient pottery (AP) made within the last 2000 years, and find that for incident light with a suitable wavelength, the AR of the leaded AP increases monotonously with the increase in the layer number of the silvery glaze (SG) media. Based on this property, we propose an optical nondestructive method for identifying the age of leaded AP by detecting the AR. By using the exhaust algorithm and the discriminant function of variance, we obtain the optimal wavelength range of the incident light to identify the ages of the leaded AP. It is found that in the visible light band, if we choose green light with a wavelength range of 540–540.1 nm as the incident light, leaded AP made within the last 2000 years can be identified swiftly and precisely by detecting the ARs. This will be useful for designing optical instruments for the fast nondestructive identification of the ages of leaded AP.

Tunneling time of an optical pulse in a photonic bandgap

Tunneling time (or group delay) for an optical pulse to transmit the energy through a photonic bandgap is calculated analytically for a one-dimensional multilayered optical superlattice. The analytical solution shows that the calculated tunneling time converges to a finite value with increasing numbers of layers, and we have derived the formula for the converged value of the tunneling time. This effect is similar to the so-called Hartman effect in a quantum system. Because of the destructive interference of multireflected light in the superlattice, the tunneling time is determined by an exponentially decaying evanescent wave, which is the reason for this effect.

Quantum phases of ultracold bosonic atoms in a one-dimensional optical superlattice

We analyze various quantum phases of ultracold bosonic atoms in a periodic one dimensional optical superlattice. Our studies have been performed using the finite size density matrix renormalization group (FS-DMRG) method in the framework of the Bose-Hubbard model. Calculations have been carried out for a wide range of densities and the energy shifts due to the superlattice potential. At commensurate fillings, we find the Mott insulator and the superfluid phases as well as Mott insulators induced by the superlattice. At a particular incommensurate density, the system is found to be in the superfluid phase coexisting with density oscillations for a certain range of parameters of the system.

Emergence of non-equilibrium superconductivity originated from repulsive interaction: Demonstration using optical lattices and implication to solid-state matter system

We study the dynamical properties of ultracold fermions in one-dimensional optical superlattices by using the adaptive time-dependent density matrix renormalization group method. The system is repulsive Hubbard model with an two-site periodic superlattice potential. Owing to superlattice structure, the ground-state states become the Mott-type insulating state at quarter-filling and band-type insulating state at half-filling, respectively. We clarify the dynamical properties of time evolution when the system is non-adiabatically changed to another lattice structure (i.e., the superlattice potential is suddenly changed to a normal one). In the case of Mott-type insulating state at quarter-filling, the time evolution exhibits a profile similar to that expected for single atom. On the other hand, we clarify the dynamical properties of a band-type insulating state at half-filling. The strongly-correlated interaction an unusual pairing of fermions induced the pair hopping process. We further address the robustness of pair hopping process and possibility of superconductivity by using sudden change from superlattice structure to normal one.

Nonadiabatic Dynamics of Ultracold Fermions in Optical Superlattices

We study the time-dependent dynamical properties of two-component ultracold fermions in a one-dimensional optical superlattice by applying the adaptive time-dependent density matrix renormalization group to a repulsive Hubbard model with an alternating superlattice potential. We clarify how the time evolution of local quantities occurs when the superlattice potential is suddenly changed to a normal one. For a Mott-type insulating state at quarter filling, the time evolution exhibits a profile similar to that expected for bosonic atoms, where correlation effects are less important. On the other hand, for a band-type insulating state at half filling, the strong repulsive interaction induces an unusual pairing of fermions, resulting in some striking properties in time evolution, such as a paired fermion co-tunneling process and the suppression of local spin moments. We further address the effect of a confining potential, which causes spatial confinement of the paired fermions.

Photo-induced dynamics of Bose–Einstein condensates in optical superlattice

The photo-induced dynamics of cold atoms in a one-dimensional optical superlattice is observed. Steady state distribution of the probability amplitudes and the site population in a one-dimensional optical superlattice is found. It is shown that this solution of the equations, which describes the temporal behavior of a Bose–Einstein condensate in a superlattice, is unstable at the sufficiently high level of boson density. The expression for the increment of modulational instability is obtained on the basis of the linear stability analysis. The numerical examples of non-stationary solutions for boson density in a superlattice for the general model are discussed as applied to both the attraction and repulsion potentials of boson interaction.

Stabilized porous silicon optical superlattices with controlled surface passivation

We report on very effective stabilization of porous silicon optical devices through a chemical surface modification technique. Such a chemical treatment proves to alter the growth of native silicon oxide on pore surfaces and thus prevents the optical device from chemical aging. As an example, we apply this technique to one-dimensional freestanding optical superlattices made of five coupled microcavities. We demonstrate how the transmission resonances of the superlattice stabilize after treatment, which implies that refractive indices in the multilayer structure remain constant. The effectiveness of the chemical surface modification technique guarantees a long-life functionality of porous silicon-based optical devices.

Defect superlattice solitons

We reveal theoretically that defect superlattice solitons (DSSs) exist at the defect site in one-dimensional optical superlattices with focusing saturable nonlinearity. Solitons with some unique properties exist in superlattices with defects. For a positive defect, solitons exist at the semi-infinite gap, and solitons are stable at low power but unstable at high power. For a negative defect, most solitons exist in the first finite gap and can propagate stably. In particular, it is found that the solitons can be divided into two equal parts upon propagation in a certain regime of parameters.

Fermionic atoms trapped in a one-dimensional optical superlattice with harmonic confinement

We study the ground-state properties of spin-1/2 fermionic atoms confined in a one-dimensional optical superlattice with harmonic confinement by using the density-matrix renormalization group method. For this purpose, we consider an ionic Hubbard model that has superlattice potentials with two-site periodicity. We find that several different types of insulating regimes coexist even if the number of atoms at each site is not an integer, but its average within the unit cell is an integer or half integer. This is contrasted to the coexisting phase of the metallic and Mott-insulating regimes known for the ordinary Hubbard model in an optical lattice. The phase characteristics are elucidated by investigating the profiles of the atom density, the local density (spin) fluctuations, the double occupation probability, and the spin correlations in detail.

Superfluid dynamics of a Bose–Einstein condensate in a one-dimensional optical superlattice

We derive and study the Bloch and Bogoliubov spectrum of a Bose–Einstein condensate (BEC) confined in a one-dimensional optical superlattice (created by interference between a primary optical lattice and a secondary optical lattice of small strength), using the Bogoliubov approximation and the hydrodynamic theory with mode coupling. We show that a BEC in an optical superlattice experiences two different tunnelling parameters and hence behaves like a diatomic chain. We derive expressions for the tunnelling parameters as a function of the strength of the primary and secondary lattice. This gives rise to a gapped branch in addition to the gapless acoustical branch in the Bogoliubov spectrum. The spectrum strongly depends on the strength of the secondary lattice, the interaction parameter and the number density of atoms. The effective mass is found to increase as the depth of the secondary optical lattice increases, a property that was utilized in Paraedes et al (2004 Nature 429 277) to achieve the Tonks–Girardeau regime. The coupling between the inhomogeneous density in the radial plane and the density modulation along the optical lattice gives rise to a multibranch Bogoliubov spectrum.

Ground-state properties of 1D Hubbard model in optical superlattice

We study the ground-state properties of a cold Fermi gas trapped in a one-dimensional optical superlattice with periodically modulated lattice potentials. By applying the density matrix renormalization group method to the Hubbard model with harmonic confinement, we compute the density profile and the spin correlation function for several different choices of superlattice potential. The ground state is characterized by the coexistence phase with the metallic and several types of Mott-insulating domains. It is shown that the spin correlation can be enhanced between the two spatially separated Mott-insulating domains.