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At least 109 records · Page 6Linked to original sources

arXiv2013

Pair-Tunneling Induced Localized Waves in a Vector Nonlinear Schrödinger Equation

We investigate the localized waves of the coupled two-mode nonlinear Schrödinger equations with a pair-tunneling term representing strongly interacting particles can tunnel between the modes as a fragmented pair. Facilitated by Darboux transformation, we have derived exact solution of nonlinear vector waves such as bright solitons, Kuznetsov-Ma soliton, Akhmediev breathers and rogue waves and demonstrated their interesting temporal-spatial structures. The phase diagram that demarcates the parameter ranges of the nonlinear waves is obtained. Our results have implications in such diverse fields as Bose-Einstein condensate, nonlinear fibers and super fluids.

nlin.PS↗

arXiv2013

Impurity-induced Dicke quantum phase transition in an impurity-doped cavity-Bose-Einstein condensate

We present a new generalized Dicke model, an impurity-doped Dicke model (IDDM), by the use of an impurity-doped cavity-Bose-Einstein condensate. It is shown that the impurity atom can induce Dicke quantum phase transition (QPT) from the normal phase to superradiant phase at a critic value of the impurity population. It is found that the IDDM exhibits continuous Dicke QPT with an infinite number of critical points, which is significantly different from that observed in the standard Dicke model with only one critical point. It is revealed that the impurity-induced Dicke QPT can happen in an arbitrary coupling regime of the cavity field and atoms while the Dicke QPT in the standard Dicke model occurs only in the strong coupling regime of the cavity field and atoms. This opens a way to observe the Dicke QPT in the intermediate and even weak coupling regime of the cavity field and atoms.

quant-ph↗

arXiv2013

Three-Body Recombination in Cold Atomic Gases

Systems of three particles show a surprising feature in their bound state spectrum: a series of geometrically scaled states, known as Efimov states. These states have not yet been observed directly, but many recent experiments show indirect evidence of their existence via the so-called recombination process. The theories that predict the Efimov states also predicts either resonant enhancement of the recombination process or suppression by destructive interference, depending on the sign of the interaction between the particles. The theories predict universal features for the Efimov states, for instance that the geometric scaling factor is 22.7, meaning that one state is 22.7 times larger than its lower lying neighbour state. This thesis seeks to investigate non-universal effects by incorporating additional information about the physical interactions into the universal theories.

physics.atom-ph↗

arXiv2013

Quantum phase transition of light in coupled optical cavity arrays: A renormalization group study

We study the quantum phase transition of light of a system when atom trapped in microcavities and interacting through the exchange of virtual photons. We predict the quantum phase transition between the photonic Coulomb blocked induce insulating phase and anisotropic exchange induced photonic superfluid phase in the system due to the existence of two Rabi frequency oscillations. The renormalization group equation shows explicitly that for this system there is no self-duality. The system also shows two Berezinskii-Kosterlitz-Thouless (BKT) transitions for the different physical situation of the system. The presence of single Rabi frequency oscillation in the system leads to the BKT transition where system shows the quantum phase transition from photonic metallic state to the Coulomb blocked induced insulating phase. For the other BKT transition when the z-component of exchange interaction is absent, the system shows the transition from the photonic metallic state to the photonic superfluid phase. We also predict the commensurate to incommensurate transition under the laser field detuning.

cond-mat.other↗

arXiv2013

Perfect screening of the inter-polaronic interaction

We consider heavy particles immersed in a Fermi sea of light fermions, and study the interaction between the heavy particles induced by the surrounding light fermions. With the Born-Oppenheimer method, we analytically show that the induced interaction between N heavy particles vanishes for any N in the limit of high light-fermion density. The induced interaction vanishes even in the unitarity regime. This suggests that the formation of N-body bound states associated with the Efimov effect is suppressed in the presence of the dense Fermi sea. We ascribe the vanishing induced interaction to the screening effect in the neutral Fermi system.

cond-mat.quant-gas↗

arXiv2013

Control of atomic transport using autoresonance

Dynamics of an atomic wavepacket in an optical superlattice is considered. We propose a simple scheme of wavepacket localization near the minima of the optical potential. In our approach, a wavelike perturbation caused by an additional lattice induces classical resonance which traps an atomic cloud. Adiabatic phase modulation of the perturbation slowly shifts resonance zone in phase space to the range of lower energies, retaining trapped atoms inside. This phenomenon is a kind of autoresonance. Quantum computations agree well with classical modelling.

nlin.CD↗

arXiv2013

Macroscopic coherence between quantum condensates formed at different times

We demonstrate macroscopic coherence between quantum condensates generated at different times, separated by more than the particle dephasing time. This is possible due to the dressed light-matter nature of exciton-polaritons, which can be injected resonantly by optical excitation at well-defined momenta. We show that the build-up of coherence between condensates depends on the interaction between the particles, particle density, as well as temperature despite the non-equilibrium nature of the condensate, whereas the mass of the particles plays no role in the condensation of resonantly injected polaritons. This experiment also makes it possible for us to measure directly the large nonlinear phase shift resulting from the polariton-polariton interaction energy. Our results provide direct evidence for coherence between different condensates and demonstrate a new approach for probing their ultrafast dynamics, opening new directions in the study of matter coherence as well as in practical applications such as quantum information and ultrafast logic.

cond-mat.quant-gas↗

arXiv2013

Tuning superfluid phases of spin-1 bosons in cubic optical lattice with linear Zeeman effect

We analyze theoretically a spinor Bose gas loaded into a three-dimensional cubic optical lattice. In order to account for different superfluid phases of spin-1 bosons in the presence of an external magnetic field, we work out a Ginzburg-Landau theory for the underlying spin-1 Bose-Hubbard model. In particular at zero temperature, we determine both the Mott and the superfluid phases for the competition between the anti-ferromagnetic interaction and the linear Zeeman effect within the validity range of the Ginzburg-Landau theory. Moreover, we find that the phase transition between the superfluid and Mott insulator phases is of second order and that the transitions between the respective superfluid phases for anti-ferromagnetic interaction can be both of first and second order.

cond-mat.quant-gas↗

arXiv2013

Nematic Metal and Antiferromagnetic Insulator on Hexagonal Kagome Lattice

Hexagonal Kagome lattice is a multiband system with a quadratic band crossing point, in contrast with honeycomb lattice with linear band crossing point, which has exotic correlated effect and can produce various novel quantum states. Here we investigate the phase diagram of the fermions on the hexagonal Kagome lattice as a function of interaction, temperature and lattice anisotropy, by combining the cellular dynamical mean-field theory with the continuous time quantum Monte Carlo method. For weak interaction, the quadratic band-crossing point is broken to linear band crossing point and the system is the semi-metal. With the increasing of the interaction, the system goes a first order transition to antiferromagnetic Mott insulator at low temperature. Below a critical temperature, due to the charge nematic fluctuation, a nematic metal forms between the weak coupling semi-metal and strong correlated Mott insulator. When the lattice anisotropy increases, the region of the nematic metal is enlarged. Furthermore, we discuss how to detect these phases in real experiments.

cond-mat.str-el↗

arXiv2013

High-Speed DC Magnetricity in Spinor Polariton Condensates

We investigate the spin dynamics of half-solitons in polariton Bose-Einstein condensates. Half-solitons, which behave as magnetic monopoles, can be accelerated in the presence of the effective magnetic field of the microcavity. We study the generation of DC magnetic currents in a gas of half-solitons. At low densities, the current is suppressed due to the dipolar oscillations. At moderate densities, a magnetic current is recovered as a consequence of the collisions between the carriers. We show a deviation from Ohm's law due to the competition between magnetic dipoles and monopoles.

cond-mat.mes-hall↗

arXiv2013

Instabilities and "phonons" of optical lattices in hollow optical fibers

Instabilities are predicted for a sufficiently long hollow photonic optical fiber, or "cavity", containing a one dimensional Bose-gas in the presence of a classical, far red-detuned, confined weak electromagnetic mode. We examine both a single beam with Bose gas (a type of Brillouin instability) and the case of a standing wave, or optical lattice. The instabilities of these driven systems have pronounced spatial structure, of combined modulational instabilities in the electromagnetic and Bose density fields. Near the critical wave vectors for the instability the coupled modes of the BEC and light can be interpreted as "phonons" of the optical lattice. We conjecture these spatially-structured instabilities for the optical lattice, which we predict at weak fields, develop into the source of spatially homogeneous heating predicted for strong fields.

cond-mat.quant-gas↗

arXiv2013

Illustration of Babinet's principle with ultracold atoms

We demonstrate Babinet's principle by the absorption of high intensity light from dense clouds of ultracold atoms. Images of the diffracted light are directly related to the spatial distribution of atoms. The advantages of employing Babinet's principle as an imaging technique are that it is easy to implement and the detected signal is large. We discuss the regimes of applicability of this technique as well as its limitations.

physics.atom-ph↗

arXiv2013

Spatiotemporal Binary Interaction and Designer quasi particle condensates

We introduce a new integrable model to investigate the dynamics of two component quasi particle condensates with spatio temporal interaction strengths. We derive the associated Lax-pair of the coupled GP equation and construct matter wave solitons. We show that the spatio temporal binary interaction strengths not only facilitate the stabilization of the condensates, but also enables one to fabricate condensates with desirable densities, geometries and properties leading to the so called "designer quasi particle condensates".

cond-mat.quant-gas↗

arXiv2013

UV-IR transmutation for hybrid realizations of Z_k parafermion systems

Recent experiments brought Majorana particles closer to reality and raised interest in realizing $\mathbb{Z}_k$ parafermions for general value of $k$ in hybrid structures. Of particular interest is the prospect of realizing a two dimensional system with the edge states described by $\mathbb{Z}_k$ parafermion conformal field theory (CFT) by coupling one dimensional hybrid systems. However in order to understand the effective perturbation due to local inter-wire coupling, it is crucial to relate short distance ultra-violet (UV) degrees of freedom to primary fields of the CFT describing long distance infra-red (IR) physics. Here we consider two recent proposals for realizing a one dimensional system described by $\mathbb{Z}_k$ parafermion CFT upon tuning to quantum critical points: a parafermion chain and a pair of $ν=2/k$ quantum Hall chiral edge states under uniform backscattering and pairing, where the latter is represented by self-dual sine-Gordon model. We explicitly derive the relation between distinct UV degrees of freedom relevant for each proposals and the primary fields of $\mathbb{Z}_3$ parafermion CFT. Our results point to a marked difference in the effect of local coupling between wires represented by each proposals, regarding robustness of the edge states in the resulting two dimensional systems.

cond-mat.str-el↗

arXiv2013

Impurity Screening and Surface Acoustic Wave Absorption in a Dipolar Exciton Condensate at Finite Temperatures

We describe the behavior of a repulsively interacting Bose-Einstein condensate of indirect dipolar exciton gas in a double quantum well (QW) system under external static or dynamic electric fields at finite temperatures. Electrostatic perturbation is considered to be created by an impurity atom or shot-range defect of QW fluctuation. The screening of this defect potential by an exciton condensate is studied. We find asymptotic spatial dependence of the screened potential and analyse its dependence on the temperature and exciton concentration. It is shown that the asymptotic of the screened potential has a steep power law dependence in contrast to the well known results of electron gas. This peculiarity reflects the bosonic nature of the exciton condensate. The behavior of exciton condensate under external alternative field created by a surface acoustic wave (SAW) is examined in detail. We focus our attention on the dependence of SAW absorption coefficient on temperature and exciton concentration. We found that at zero temperatures Landau damping does not contribute to the SAW absorption, but the Belyaev mechanism produces unusual behavior of SAW absorption coefficient on exciton concentration: if the exciton concentration exceeds some critical value, the SAW absorption vanishes. At finite temperatures Landau damping comes into action and results in washing out the sharp absorption behavior. Such unusual SAW absorption properties can be used for experimental evidence of the exciton condensation. This method is also applicable to the experimental testing of both dark and bright exciton condensates, that is impossible to do with the optical luminescence technique.

cond-mat.mes-hall↗

arXiv2013

Magneto--optical matter wave Bragg diffraction

We have performed a principle-proof-experiment of a magneto-optical diffraction (MOD) technique that requires no energy level splitting by homogeneous magnetic field and a circularly polarized optical lattice, avoiding system errors in an interferometer based on the MOD. The principle for this new MOD is that asynchronized switching of quadrupole trap and Ioffe trap in a quadrupole-Ioffe-configuration trap can generate a residual magnetic force to drive a Bose-Einstein condensate (BEC) to move. We have observed asymmetric atomic diffraction resulting from the asymmetric distribution of the Bloch eigenstates involved in the diffraction process when the condensate is driven by such a force, and matter-wave self-imaging due to coherent population oscillation of the dominantly occupied Bloch eigenstates. We have classified the mechanisms that lead to symmetric or asymmetric diffraction, and found that our experiment presents a magnetic alternative to a moving optical lattice, with a great potential to achieve a very large momentum transfer ($>110 \hbar k$) to a BEC using well-developed magnetic trapping techniques.

cond-mat.quant-gas↗

arXiv2013

Optical Lattice Emulators: Bose and Fermi Hubbard Models

This chapter is a pedagogical review of the Hubbard model for bosons with repulsion and for fermions with attraction and repulsion primarily using two methods, one chosen for its simplicity and insights (mean field theory) and the other chosen for its accuracy and reliability (quantum Monte Marlo methods). From a comparison of the two methods we glean valuable information into the effects of fluctuations that dominate quantum phase transitions. The chapter includes an in-depth comparison with experiments. We conclude with a discussion of future developments where the technical methods expounded on here, mean field theory and quantum Monte Carlo, could be useful.

cond-mat.quant-gas↗

arXiv2013

Dark soliton in quasi-one-dimensional Bose-Einstein condensates with a Gaussian trap

In this paper we study dark solitons in quasi-one-dimensional Bose-Einstein condensates (BECs) in presence of an anharmonic external potential. The theoretical model is based on the Muñoz-Mateo and Delgado (MMD) equation that describes cigar-shaped BECs with repulsive interatomic interactions. Since MMD equation presents a nonpolynomial form, the soliton-sound recombination cannot display the same pattern presented in the cubic model. We perform numerical simulations to compare both cases.

cond-mat.quant-gas↗