Hypergeometric continuation of divergent perturbation series: I. Critical exponents of the Bose-Hubbard model

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Sanders, Sören; Holthaus, Martin

2017-10-01

We study the connection between the exponent of the order parameter of the Mott insulator-to-superfluid transition occurring in the two-dimensional Bose-Hubbard model, and the divergence exponents of its one- and two-particle correlation functions. We find that at the multicritical points all divergence exponents are related to each other, allowing us to express the critical exponent in terms of one single divergence exponent. This approach correctly reproduces the critical exponent of the three-dimensional XY universality class. Because divergence exponents can be computed in an efficient manner by hypergeometric analytic continuation, our strategy is applicable to a wide class of systems.

Simultaneous diagonal and off-diagonal order in the Bose-Hubbard Hamiltonian

International Nuclear Information System (INIS)

Scalettar, R.T.; Batrouni, G.G.; Kampf, A.P.; Zimanyi, G.T.

1995-01-01

The Bose-Hubbard model exhibits a rich phase diagram consisting both of insulating regimes where diagonal long-range (solid) order dominates as well as conducting regimes where off-diagonal long-range order (superfluidity) is present. In this paper we describe the results of quantum Monte Carlo calculations of the phase diagram, both for the hard- and soft-core cases, with a particular focus on the possibility of simultaneous superfluid and solid order. We also discuss the appearance of phase separation in the model. The simulations are compared with analytic calculations of the phase diagram and spin-wave dispersion

Quantum phase transitions of light in a dissipative Dicke-Bose-Hubbard model

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Wu, Ren-Cun; Tan, Lei; Zhang, Wen-Xuan; Liu, Wu-Ming

2017-09-01

The impact that the environment has on the quantum phase transition of light in the Dicke-Bose-Hubbard model is investigated. Based on the quasibosonic approach, mean-field theory, and perturbation theory, the formulation of the Hamiltonian, the eigenenergies, and the superfluid order parameter are obtained analytically. Compared with the ideal cases, the order parameter of the system evolves with time as the photons naturally decay in their environment. When the system starts with the superfluid state, the dissipation makes the photons more likely to localize, and a greater hopping energy of photons is required to restore the long-range phase coherence of the localized state of the system. Furthermore, the Mott lobes depend crucially on the numbers of atoms and photons (which disappear) of each site, and the system tends to be classical with the number of atoms increasing; however, the atomic number is far lower than that expected under ideal circumstances. As there is an inevitable interaction between the coupled-cavity array and its surrounding environment in the actual experiments, the system is intrinsically dissipative. The results obtained here provide a more realistic image for characterizing the dissipative nature of quantum phase transitions in lossy platforms, which will offer valuable insight into quantum simulation of a dissipative system and which are helpful in guiding experimentalists in open quantum systems.

Quantum behaviour of open pumped and damped Bose-Hubbard trimers

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Chianca, C. V.; Olsen, M. K.

2018-01-01

We propose and analyse analogs of optical cavities for atoms using three-well inline Bose-Hubbard models with pumping and losses. With one well pumped and one damped, we find that both the mean-field dynamics and the quantum statistics show a qualitative dependence on the choice of damped well. The systems we analyse remain far from equilibrium, although most do enter a steady-state regime. We find quadrature squeezing, bipartite and tripartite inseparability and entanglement, and states exhibiting the EPR paradox, depending on the parameter regimes. We also discover situations where the mean-field solutions of our models are noticeably different from the quantum solutions for the mean fields. Due to recent experimental advances, it should be possible to demonstrate the effects we predict and investigate in this article.

Floquet Engineering of Correlated Tunneling in the Bose-Hubbard Model with Ultracold Atoms.

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Meinert, F; Mark, M J; Lauber, K; Daley, A J; Nägerl, H-C

2016-05-20

We report on the experimental implementation of tunable occupation-dependent tunneling in a Bose-Hubbard system of ultracold atoms via time-periodic modulation of the on-site interaction energy. The tunneling rate is inferred from a time-resolved measurement of the lattice site occupation after a quantum quench. We demonstrate coherent control of the tunneling dynamics in the correlated many-body system, including full suppression of tunneling as predicted within the framework of Floquet theory. We find that the tunneling rate explicitly depends on the atom number difference in neighboring lattice sites. Our results may open up ways to realize artificial gauge fields that feature density dependence with ultracold atoms.

Propagation of quantum correlations after a quench in the Mott-insulator regime of the Bose-Hubbard model

International Nuclear Information System (INIS)

Krutitsky, Konstantin V.; Navez, Patrick; Schuetzhold, Ralf; Queisser, Friedemann

2014-01-01

We study a quantum quench in the Bose-Hubbard model where the tunneling rate J is suddenly switched from zero to a finite value in the Mott regime. In order to solve the many-body quantum dynamics far from equilibrium, we consider the reduced density matrices for a finite number of lattice sites and split them up into on-site density operators, i.e., the mean field, plus two-point and three-point correlations etc. Neglecting three-point and higher correlations, we are able to numerically simulate the time-evolution of the on-site density matrices and the two-point quantum correlations (e.g., their effective light-cone structure) for a comparably large number of lattice sites. (orig.)

Stochastic mean-field theory: Method and application to the disordered Bose-Hubbard model at finite temperature and speckle disorder

International Nuclear Information System (INIS)

Bissbort, Ulf; Hofstetter, Walter; Thomale, Ronny

2010-01-01

We discuss the stochastic mean-field theory (SMFT) method, which is a new approach for describing disordered Bose systems in the thermodynamic limit including localization and dimensional effects. We explicate the method in detail and apply it to the disordered Bose-Hubbard model at finite temperature, with on-site box disorder, as well as experimentally relevant unbounded speckle disorder. We find that disorder-induced condensation and re-entrant behavior at constant filling are only possible at low temperatures, beyond the reach of current experiments [M. Pasienski, D. McKay, M. White, and B. DeMarco, e-print arXiv:0908.1182]. Including off-diagonal hopping disorder as well, we investigate its effect on the phase diagram in addition to pure on-site disorder. To make connection to present experiments on a quantitative level, we also combine SMFT with an LDA approach and obtain the condensate fraction in the presence of an external trapping potential.

Exact results and conjectures on the adiabatic Holstein-Hubbard model at large electron-phonon coupling

International Nuclear Information System (INIS)

Aubry, S.

1993-01-01

Principles and notations of the Holstein-Hubbard model in a magnetic field are first reviewed. Effects of the dimensionality, the lattice discreteness and the magnetic field on single polarons, are examined and the existence of many polarons and bipolarons structures at large electron-phonon coupling is discussed. Properties of bipolaronic and polaronic structures are examined together with the magnetic field effects on these structures. High Tc superconductivity resulting from the competition between the electron-phonon and Hubbard couplings is discussed. 7 figs., 18 refs

Super-Hubbard models and applications

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Drummond, James M.; Feverati, Giovanni; Frappat, Luc; Ragoucy, Eric

2007-01-01

We construct XX- and Hubbard-like models based on unitary superalgebras gl(N/M) generalising Shastry's and Maassarani's approach of the algebraic case. We introduce the R-matrix of the gl(N/M) XX model and that of the Hubbard model defined by coupling two independent XX models. In both cases, we show that the R-matrices satisfy the Yang-Baxter equation, we derive the corresponding local Hamiltonian in the transfer matrix formalism and we determine the symmetry of the Hamiltonian. Explicit examples are worked out. In the cases of the gl(1/2) and gl(2/2) Hubbard models, a perturbative calculation at two loops a la Klein and Seitz is performed

Effective action for superfluid Fermi systems in the strong-coupling limit

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Dupuis, N.

2005-07-01

We derive the low-energy effective action for three-dimensional superfluid Fermi systems in the strong-coupling limit, where superfluidity originates from Bose-Einstein condensation of composite bosons. Taking into account density and pairing fluctuations on the same footing, we show that the effective action involves only the fermion density ρr and its conjugate variable, the phase θr of the pairing order parameter Δr . We recover the standard action of a Bose superfluid of density ρr/2 , where the bosons have a mass mB=2m and interact via a repulsive contact potential with amplitude gB=4πaB/mB,aB=2a ( a the s -wave scattering length associated to the fermion-fermion interaction in vacuum). For lattice models, the derivation of the effective action is based on the mapping of the attractive Hubbard model onto the Heisenberg model in a uniform magnetic field, and a coherent state path integral representation of the partition function. The effective description of the Fermi superfluid in the strong-coupling limit is a Bose-Hubbard model with an intersite hopping amplitude tB=J/2 and an on-site repulsive interaction UB=2Jz , where J=4t2/U ( t and -U are the intersite hopping amplitude and the on-site attraction in the (fermionic) Hubbard model, z the number of nearest-neighbor sites).

Effective action for superfluid Fermi systems in the strong-coupling limit

International Nuclear Information System (INIS)

Dupuis, N.

2005-01-01

We derive the low-energy effective action for three-dimensional superfluid Fermi systems in the strong-coupling limit, where superfluidity originates from Bose-Einstein condensation of composite bosons. Taking into account density and pairing fluctuations on the same footing, we show that the effective action involves only the fermion density ρ r and its conjugate variable, the phase θ r of the pairing order parameter Δ r . We recover the standard action of a Bose superfluid of density ρ r /2, where the bosons have a mass m B =2m and interact via a repulsive contact potential with amplitude g B =4πa B /m B ,a B =2a (a the s-wave scattering length associated to the fermion-fermion interaction in vacuum). For lattice models, the derivation of the effective action is based on the mapping of the attractive Hubbard model onto the Heisenberg model in a uniform magnetic field, and a coherent state path integral representation of the partition function. The effective description of the Fermi superfluid in the strong-coupling limit is a Bose-Hubbard model with an intersite hopping amplitude t B =J/2 and an on-site repulsive interaction U B =2Jz, where J=4t 2 /U (t and -U are the intersite hopping amplitude and the on-site attraction in the (fermionic) Hubbard model, z the number of nearest-neighbor sites)

Fermionic Hubbard model with Rashba or Dresselhaus spin-orbit coupling

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Sun, Fadi; Ye, Jinwu; Liu, Wu-Ming

2017-06-01

In this work, we investigate the possible dramatic effects of Rashba or Dresselhaus spin-orbit coupling (SOC) on the fermionic Hubbard model in a two-dimensional square lattice. In the strong coupling limit, it leads to the rotated antiferromagnetic Heisenberg model which is a new class of quantum spin model. For a special equivalent class, we identify a new spin-orbital entangled commensurate ground (Y-y) state subject to strong quantum fluctuations at T = 0. We evaluate the quantum fluctuations by the spin wave expansion up to order 1/{S}2. In some SOC parameter regimes, the Y-y state supports a massive relativistic incommensurate magnon (C-IC) with its two gap minima positions continuously tuned by the SOC parameters. The C-IC magnons dominate all the low temperature thermodynamic quantities and also lead to the separation of the peak positions between the longitudinal and the transverse spin structure factors. In the weak coupling limit, any weak repulsive interaction also leads to a weak Y-y state. There is only a crossover from the weak to the strong coupling. High temperature expansions of the specific heats in both weak and strong coupling are presented. The dramatic roles to be played by these C-IC magnons at generic SOC parameters or under various external probes are hinted at. Experimental applications to both layered noncentrosymmetric materials and cold atoms are discussed.

Slave-boson method for the Hubbard model: Resonating-valence-bond state and high-temperature superconductivity

International Nuclear Information System (INIS)

Kapitonov, V.S.

1991-01-01

This paper offers a formulation of mean-field theory for the Hubbard model that is different from the one developed in the work of Anderson. The modified slave-boson method is used. The advantage of the method is that it is not necessary to exclude doubly occupied sites by using the approximately canonical transformation. In the proposed theory, Cooper pairs and the energy gap are a result of the condensation of the slave Bose field that describes doubly occupied sites. Here, the modified slave-boson method is used to describe the metal-insulator and metal-superconductor phase transitions in the Hubbard model. Expressions are derived for the energy gap and phase-transition temperature

The symmetry of the Hubbard model

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Grosse, H.

1988-01-01

The spectrum of the Hubbard model shows permanent degeneracy of levels with different symmetry, if one considers only symmetry operators independent of the coupling constant. This suggests the existence of symmetry operators which depend on the coupling constant. We find these highly nontrivial operators and show that they explain the degeneracies in the energy spectrum. 5 refs. (Author)

An introduction to the Hubbard model

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Ercolessi, E.; Morandi, G.; Pieri, P.

1997-01-01

In these notes we review some of the basic features of the 2D Hubbard model, thought of as the appropriate model for the description of the Cu - O planes in the cuprate superconductors. We discuss breifly the weak-coupling regime of the model and, in the opposite limit, the mapping of the one band Hubbard model onto an AFM Heisenberg model at half filling and onto the t - J model below half filling. We discuss next Emery's three band model and its mapping onto the so-called ''spin-fermion'' model. Its continuum limit is discussed by making use of an adiabatic followed by a gradient expansion. We review briefly how the model maps onto a nonlinear sigma model and some of the features of the latter. (orig.)

Investigation of a four-body coupling in the one-dimensional extended Penson-Kolb-Hubbard model

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Ding, Hanqin; Ma, Xiaojuan; Zhang, Jun

2017-09-01

The experimental advances in cold fermion gases motivates the investigation of a one-dimensional (1D) correlated electronic system by incorporating a four-body coupling. Using the low-energy field theory scheme and focusing on the weak-coupling regime, we extend the 1D Penson-Kolb-Hubbard (PKH) model at half filling. It is found that the additional four-body interaction may significantly modify the quantum phase diagram, favoring the presence of the superconducting phase even in the case of two-body repulsions.

Deterministic Many-Resonator W Entanglement of Nearly Arbitrary Microwave States via Attractive Bose-Hubbard Simulation

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A. A. Gangat

2013-08-01

Full Text Available Multipartite entanglement of large numbers of physically distinct linear resonators is of both fundamental and applied interest, but there have been no feasible proposals to date for achieving it. At the same time, the Bose-Hubbard model with attractive interactions (ABH is theoretically known to have a phase transition from the superfluid phase to a highly entangled nonlocal superposition, but observation of this phase transition has remained out of experimental reach. In this theoretical work, we jointly address these two problems by (1 proposing an experimentally accessible quantum simulation of the ABH phase transition in an array of tunably coupled superconducting circuit microwave resonators and (2 incorporating the simulation into a highly scalable protocol that takes as input any microwave-resonator state with negligible occupation of number states |0⟩ and |1⟩ and nonlocally superposes it across the whole array of resonators. The large-scale multipartite entanglement produced by the protocol is of the W type, which is well known for its robustness. The protocol utilizes the ABH phase transition to generate the multipartite entanglement of all of the resonators in parallel, and is therefore deterministic and permits an increase in resonator number without any increase in protocol complexity; the number of resonators is limited instead by system characteristics such as resonator-frequency disorder and inter-resonator coupling strength. Only one local and two global controls are required for the protocol. We numerically demonstrate the protocol with realistic system parameters and estimate that current experimental capabilities can realize the protocol with high fidelity for greater than 40 resonators. Because superconducting-circuit microwave resonators are capable of interfacing with other devices and platforms such as mechanical resonators and (potentially optical fields, this proposal provides a route toward large-scale W

Extended Hubbard models for ultracold atoms in optical lattices

International Nuclear Information System (INIS)

Juergensen, Ole

2015-01-01

In this thesis, the phase diagrams and dynamics of various extended Hubbard models for ultracold atoms in optical lattices are studied. Hubbard models are the primary description for many interacting particles in periodic potentials with the paramount example of the electrons in solids. The very same models describe the behavior of ultracold quantum gases trapped in the periodic potentials generated by interfering beams of laser light. These optical lattices provide an unprecedented access to the fundamentals of the many-particle physics that govern the properties of solid-state materials. They can be used to simulate solid-state systems and validate the approximations and simplifications made in theoretical models. This thesis revisits the numerous approximations underlying the standard Hubbard models with special regard to optical lattice experiments. The incorporation of the interaction between particles on adjacent lattice sites leads to extended Hubbard models. Offsite interactions have a strong influence on the phase boundaries and can give rise to novel correlated quantum phases. The extended models are studied with the numerical methods of exact diagonalization and time evolution, a cluster Gutzwiller approximation, as well as with the strong-coupling expansion approach. In total, this thesis demonstrates the high relevance of beyond-Hubbard processes for ultracold atoms in optical lattices. Extended Hubbard models can be employed to tackle unexplained problems of solid-state physics as well as enter previously inaccessible regimes.

Extended Hubbard models for ultracold atoms in optical lattices

Energy Technology Data Exchange (ETDEWEB)

Juergensen, Ole

2015-06-05

In this thesis, the phase diagrams and dynamics of various extended Hubbard models for ultracold atoms in optical lattices are studied. Hubbard models are the primary description for many interacting particles in periodic potentials with the paramount example of the electrons in solids. The very same models describe the behavior of ultracold quantum gases trapped in the periodic potentials generated by interfering beams of laser light. These optical lattices provide an unprecedented access to the fundamentals of the many-particle physics that govern the properties of solid-state materials. They can be used to simulate solid-state systems and validate the approximations and simplifications made in theoretical models. This thesis revisits the numerous approximations underlying the standard Hubbard models with special regard to optical lattice experiments. The incorporation of the interaction between particles on adjacent lattice sites leads to extended Hubbard models. Offsite interactions have a strong influence on the phase boundaries and can give rise to novel correlated quantum phases. The extended models are studied with the numerical methods of exact diagonalization and time evolution, a cluster Gutzwiller approximation, as well as with the strong-coupling expansion approach. In total, this thesis demonstrates the high relevance of beyond-Hubbard processes for ultracold atoms in optical lattices. Extended Hubbard models can be employed to tackle unexplained problems of solid-state physics as well as enter previously inaccessible regimes.

Current reversals and metastable states in the infinite Bose-Hubbard chain with local particle loss

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Kiefer-Emmanouilidis, M.; Sirker, J.

2017-12-01

We present an algorithm which combines the quantum trajectory approach to open quantum systems with a density-matrix renormalization-group scheme for infinite one-dimensional lattice systems. We apply this method to investigate the long-time dynamics in the Bose-Hubbard model with local particle loss starting from a Mott-insulating initial state with one boson per site. While the short-time dynamics can be described even quantitatively by an equation of motion (EOM) approach at the mean-field level, many-body interactions lead to unexpected effects at intermediate and long times: local particle currents far away from the dissipative site start to reverse direction ultimately leading to a metastable state with a total particle current pointing away from the lossy site. An alternative EOM approach based on an effective fermion model shows that the reversal of currents can be understood qualitatively by the creation of holon-doublon pairs at the edge of the region of reduced particle density. The doublons are then able to escape while the holes move towards the dissipative site, a process reminiscent—in a loose sense—of Hawking radiation.

Attractive Hubbard model with disorder and the generalized Anderson theorem

International Nuclear Information System (INIS)

Kuchinskii, E. Z.; Kuleeva, N. A.; Sadovskii, M. V.

2015-01-01

Using the generalized DMFT+Σ approach, we study the influence of disorder on single-particle properties of the normal phase and the superconducting transition temperature in the attractive Hubbard model. A wide range of attractive potentials U is studied, from the weak coupling region, where both the instability of the normal phase and superconductivity are well described by the BCS model, to the strong-coupling region, where the superconducting transition is due to Bose-Einstein condensation (BEC) of compact Cooper pairs, formed at temperatures much higher than the superconducting transition temperature. We study two typical models of the conduction band with semi-elliptic and flat densities of states, respectively appropriate for three-dimensional and two-dimensional systems. For the semi-elliptic density of states, the disorder influence on all single-particle properties (e.g., density of states) is universal for an arbitrary strength of electronic correlations and disorder and is due to only the general disorder widening of the conduction band. In the case of a flat density of states, universality is absent in the general case, but still the disorder influence is mainly due to band widening, and the universal behavior is restored for large enough disorder. Using the combination of DMFT+Σ and Nozieres-Schmitt-Rink approximations, we study the disorder influence on the superconducting transition temperature T c for a range of characteristic values of U and disorder, including the BCS-BEC crossover region and the limit of strong-coupling. Disorder can either suppress T c (in the weak-coupling region) or significantly increase T c (in the strong-coupling region). However, in all cases, the generalized Anderson theorem is valid and all changes of the superconducting critical temperature are essentially due to only the general disorder widening of the conduction band

Classical mapping for Hubbard operators: Application to the double-Anderson model

Energy Technology Data Exchange (ETDEWEB)

Li, Bin; Miller, William H. [Department of Chemistry and Kenneth S. Pitzer Center for Theoretical Chemistry, University of California, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States); Levy, Tal J.; Rabani, Eran [School of Chemistry, The Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)

2014-05-28

A classical Cartesian mapping for Hubbard operators is developed to describe the nonequilibrium transport of an open quantum system with many electrons. The mapping of the Hubbard operators representing the many-body Hamiltonian is derived by using analogies from classical mappings of boson creation and annihilation operators vis-à-vis a coherent state representation. The approach provides qualitative results for a double quantum dot array (double Anderson impurity model) coupled to fermionic leads for a range of bias voltages, Coulomb couplings, and hopping terms. While the width and height of the conduction peaks show deviations from the master equation approach considered to be accurate in the limit of weak system-leads couplings and high temperatures, the Hubbard mapping captures all transport channels involving transition between many electron states, some of which are not captured by approximate nonequilibrium Green function closures.

Spin-Orbit Coupled Bose-Einstein Condensates

Science.gov (United States)

2016-11-03

21. "Many-body physics of spin-orbit-coupled quantum gases ," Invited talk at the March Meeting 2014 in Denver, Colorado (March, 2014) 22... properties of the fundamentally new class of coherent states of quantum matter that had been predicted by the PI and subsequently experimentally...Report Title This ARO research proposal entitled "SPIN-ORBIT COUPLED BOSE-EINSTEIN CONDENSATES" (SOBECs) explored properties of the fundamentally new

Noise thermometry with two weakly coupled Bose-Einstein condensates.

Science.gov (United States)

Gati, Rudolf; Hemmerling, Börge; Fölling, Jonas; Albiez, Michael; Oberthaler, Markus K

2006-04-07

Here we report on the experimental investigation of thermally induced fluctuations of the relative phase between two Bose-Einstein condensates which are coupled via tunneling. The experimental control over the coupling strength and the temperature of the thermal background allows for the quantitative analysis of the phase fluctuations. Furthermore, we demonstrate the application of these measurements for thermometry in a regime where standard methods fail. With this we confirm that the heat capacity of an ideal Bose gas deviates from that of a classical gas as predicted by the third law of thermodynamics.

Noise Thermometry with Two Weakly Coupled Bose-Einstein Condensates

International Nuclear Information System (INIS)

Gati, Rudolf; Hemmerling, Boerge; Foelling, Jonas; Albiez, Michael; Oberthaler, Markus K.

2006-01-01

Here we report on the experimental investigation of thermally induced fluctuations of the relative phase between two Bose-Einstein condensates which are coupled via tunneling. The experimental control over the coupling strength and the temperature of the thermal background allows for the quantitative analysis of the phase fluctuations. Furthermore, we demonstrate the application of these measurements for thermometry in a regime where standard methods fail. With this we confirm that the heat capacity of an ideal Bose gas deviates from that of a classical gas as predicted by the third law of thermodynamics

Ground State of Bosons in Bose-Fermi Mixture with Spin-Orbit Coupling

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Sakamoto, Ryohei; Ono, Yosuke; Hatsuda, Rei; Shiina, Kenta; Arahata, Emiko; Mori, Hiroyuki

2017-07-01

We study an effect of spin-1/2 fermions on the ground state of a Bose system with equal Rashba and Dresselhaus spin-orbit coupling. By using mean-field and tight-binding approximations, we show the ground state phase diagram of the Bose system in the spin-orbit coupled Bose-Fermi mixture and find that the characteristic phase domain, where a spin current of fermions may be induced, can exist even in the presence of a significantly large number of fermions.

Bose-Einstein condensation and applications

International Nuclear Information System (INIS)

Jaksch, D.H.

1999-10-01

After a short introduction on recent developments in the field of Bose-Einstein condensation (BEC) with weakly interacting neutral atoms in the first part of my thesis I investigate the properties of a BEC in its stationary state with the help of quantum kinetic theory in the second part. Especially, I consider the particle number and phase fluctuations of a BEC emerging from the interaction of the condensed particles with the thermal cloud of atoms. In the third part of my thesis I show how one might realize the Bose-Hubbard model in optical lattices by making use of BEC. In the last part of my work I show how one can realize quantum logic with neutral atoms trapped in either optical lattices or in magnetic microtraps. (author)

Emulating the 1-dimensional Fermi-Hubbard model with superconducting qubits

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Reiner, Jan-Michael; Marthaler, Michael; Schoen, Gerd [Institut fuer Theoretische Festkoerperphysik, Karlsruhe Institute of Technology (KIT), 76131 Karlsruhe (Germany)

2016-07-01

A chain of qubits with both ZZ and XX couplings is described by a Hamiltonian which coincides with the Fermi-Hubbard model in one dimension. The qubit system can thus be used to study the quantum properties of this model. We investigate the specific implementation of such an analog quantum simulator by a chain of tunable Transmon qubits, where the ZZ interaction arises due to an inductive coupling and the XX interaction due to a capacitive coupling.

Extended Hubbard model for mesoscopic transport in donor arrays in silicon

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Le, Nguyen H.; Fisher, Andrew J.; Ginossar, Eran

2017-12-01

Arrays of dopants in silicon are promising platforms for the quantum simulation of the Fermi-Hubbard model. We show that the simplest model with only on-site interaction is insufficient to describe the physics of an array of phosphorous donors in silicon due to the strong intersite interaction in the system. We also study the resonant tunneling transport in the array at low temperature as a mean of probing the features of the Hubbard physics, such as the Hubbard bands and the Mott gap. Two mechanisms of localization which suppresses transport in the array are investigated: The first arises from the electron-ion core attraction and is significant at low filling; the second is due to the sharp oscillation in the tunnel coupling caused by the intervalley interference of the donor electron's wave function. This disorder in the tunnel coupling leads to a steep exponential decay of conductance with channel length in one-dimensional arrays, but its effect is less prominent in two-dimensional ones. Hence, it is possible to observe resonant tunneling transport in a relatively large array in two dimensions.

Physical properties of the half-filled Hubbard model in infinite dimensions

International Nuclear Information System (INIS)

Georges, A.; Krauth, W.

1993-01-01

A detailed quantitative study of the physical properties of the infinite-dimensional Hubbard model at half filling is presented. The method makes use of an exact mapping onto a single-impurity model supplemented by a self-consistency condition. This coupled problem is solved numerically. Results for thermodynamic quantities (specific heat, entropy, . . .), one-particle spectral properties, and magnetic properties (response to a uniform magnetic field) are presented and discussed. The nature of the Mott-Hubbard metal-insulator transition found in this model is investigated. A numerical solution of the mean-field equations inside the antiferromagnetic phase is also reported

Effective electron-electron and electron-phonon interactions in the Hubbard-Holstein model

International Nuclear Information System (INIS)

Aprea, G.; Di Castro, C.; Grilli, M. . E-mail marco.grilli@roma1.infn.it; Lorenzana, J.

2006-01-01

We investigate the interplay between the electron-electron and the electron-phonon interaction in the Hubbard-Holstein model. We implement the flow-equation method to investigate within this model the effect of correlation on the electron-phonon effective coupling and, conversely, the effect of phonons in the effective electron-electron interaction. Using this technique we obtain analytical momentum-dependent expressions for the effective couplings and we study their behavior for different physical regimes. In agreement with other works on this subject, we find that the electron-electron attraction mediated by phonons in the presence of Hubbard repulsion is peaked at low transferred momenta. The role of the characteristic energies involved is also analyzed

The role of local repulsion in superconductivity in the Hubbard-Holstein model

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Lin, Chungwei; Wang, Bingnan; Teo, Koon Hoo

2017-01-01

We examine the superconducting solution in the Hubbard-Holstein model using Dynamical Mean Field Theory. The Holstein term introduces the site-independent Boson fields coupling to local electron density, and has two competing influences on superconductivity: The Boson field mediates the effective electron-electron attraction, which is essential for the S-wave electron pairing; the same coupling to the Boson fields also induces the polaron effect, which makes the system less metallic and thus suppresses superconductivity. The Hubbard term introduces an energy penalty U when two electrons occupy the same site, which is expected to suppress superconductivity. By solving the Hubbard-Holstein model using Dynamical Mean Field theory, we find that the Hubbard U can be beneficial to superconductivity under some circumstances. In particular, we demonstrate that when the Boson energy Ω is small, a weak local repulsion actually stabilizesthe S-wave superconducting state. This behavior can be understood as an interplay between superconductivity, the polaron effect, and the on-site repulsion: As the polaron effect is strong and suppresses superconductivity in the small Ω regime, the weak on-site repulsion reduces the polaron effect and effectively enhances superconductivity. Our calculation elucidates the role of local repulsion in the conventional S-wave superconductors.

Hanle model of a spin-orbit coupled Bose-Einstein condensate of excitons in semiconductor quantum wells

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Andreev, S. V.; Nalitov, A. V.

2018-04-01

We present a theoretical model of a driven-dissipative spin-orbit coupled Bose-Einstein condensate of indirect excitons in semiconductor quantum wells (QW's). Our steady-state solution of the problem shares analogies with the Hanle effect in an optical orientation experiment. The role of the spin pump in our case is played by Bose-stimulated scattering into a linearly-polarized ground state and the depolarization occurs as a result of exchange interaction between electrons and holes. Our theory agrees with the recent experiment [A. A. High et al., Phys. Rev. Lett. 110, 246403 (2013), 10.1103/PhysRevLett.110.246403], where spontaneous emergence of spatial coherence and polarization textures have been observed. As a complementary test, we discuss a configuration where an external magnetic field is applied in the structure plane.

Pseudo-steady-state non-Gaussian Einstein-Podolsky-Rosen steering of massive particles in pumped and damped Bose-Hubbard dimers

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Olsen, M. K.

2017-02-01

We propose and analyze a pumped and damped Bose-Hubbard dimer as a source of continuous-variable Einstein-Podolsky-Rosen (EPR) steering with non-Gaussian statistics. We use and compare the results of the approximate truncated Wigner and the exact positive-P representation to calculate and compare the predictions for intensities, second-order quantum correlations, and third- and fourth-order cumulants. We find agreement for intensities and the products of inferred quadrature variances, which indicate that states demonstrating the EPR paradox are present. We find clear signals of non-Gaussianity in the quantum states of the modes from both the approximate and exact techniques, with quantitative differences in their predictions. Our proposed experimental configuration is extrapolated from current experimental techniques and adds another apparatus to the current toolbox of quantum atom optics.

Exchange and spin-fluctuation superconducting pairing in the strong correlation limit of the Hubbard model

International Nuclear Information System (INIS)

Plakida, N. M.; Anton, L.; Adam, S. . Department of Theoretical Physics, Horia Hulubei National Institute for Physics and Nuclear Engineering, PO Box MG-6, RO-76900 Bucharest - Magurele; RO); Adam, Gh. . Department of Theoretical Physics, Horia Hulubei National Institute for Physics and Nuclear Engineering, PO Box MG-6, RO-76900 Bucharest - Magurele; RO)

2001-01-01

A microscopical theory of superconductivity in the two-band singlet-hole Hubbard model, in the strong coupling limit in a paramagnetic state, is developed. The model Hamiltonian is obtained by projecting the p-d model to an asymmetric Hubbard model with the lower Hubbard subband occupied by one-hole Cu d-like states and the upper Hubbard subband occupied by two-hole p-d singlet states. The model requires two microscopical parameters only, the p-d hybridization parameter t and the charge-transfer gap Δ. It was previously shown to secure an appropriate description of the normal state properties of the high -T c cuprates. To treat rigorously the strong correlations, the Hubbard operator technique within the projection method for the Green function is used. The Dyson equation is derived. In the molecular field approximation, d-wave superconducting pairing of conventional hole (electron) pairs in one Hubbard subband is found, which is mediated by the exchange interaction given by the interband hopping, J ij = 4 (t ij ) 2 / Δ. The normal and anomalous components of the self-energy matrix are calculated in the self-consistent Born approximation for the electron-spin-fluctuation scattering mediated by kinematic interaction of the second order of the intraband hopping. The derived numerical and analytical solutions predict the occurrence of singlet d x 2 -y 2 -wave pairing both in the d-hole and singlet Hubbard subbands. The gap functions and T c are calculated for different hole concentrations. The exchange interaction is shown to be the most important pairing interaction in the Hubbard model in the strong correlation limit, while the spin-fluctuation coupling results only in a moderate enhancement of T c . The smaller weight of the latter comes from two specific features: its vanishing inside the Brillouin zone (BZ) along the lines, |k x | + |k y |=π pointing towards the hot spots and the existence of a small energy shell within which the pairing is effective. By

Pairing and superconductivity from weak to strong coupling in the attractive Hubbard model

International Nuclear Information System (INIS)

Toschi, A; Barone, P; Capone, M; Castellani, C

2005-01-01

The finite-temperature phase diagram of the attractive Hubbard model is studied by means of the dynamical mean-field theory. We first consider the normal phase of the model by explicitly frustrating the superconducting ordering. In this case, we obtain a first-order pairing transition between a metallic phase and a paired phase formed by strongly coupled incoherent pairs. The transition line ends in a finite temperature critical point, but a crossover between two qualitatively different solutions still occurs at higher temperature. Comparing the superconducting- and the normal-phase solutions, we find that the superconducting instability always occurs before the pairing transition in the normal phase, i.e. T c > T pairing . Nevertheless, the high-temperature phase diagram at T > T c is still characterized by a crossover from a metallic phase to a preformed pair phase. We characterize this crossover by computing different observables that can be used to identify the pseudogap region, like the spin susceptibility, the specific heat and the single-particle spectral function

Pairing tendencies in a two-orbital Hubbard model in one dimension

Energy Technology Data Exchange (ETDEWEB)

Patel, Niravkumar D. [The Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Nocera, Adriana [The Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Alvarez, Gonzalo [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Moreo, A. [The Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Dagotto, Elbio R. [The Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-07-31

The recent discovery of superconductivity under high pressure in the ladder compound BaFe2S3 has opened a new field of research in iron-based superconductors with focus on quasi-one-dimensional geometries. In this publication, using the density matrix renormalization group technique, we study a two-orbital Hubbard model defined in one-dimensional chains. Our main result is the presence of hole binding tendencies at intermediate Hubbard U repulsion and robust Hund coupling J_H / U = 0.25. Binding does not occur either in weak coupling or at very strong coupling. The pair-pair correlations that are dominant near half-filling, or of similar strength as the charge and spin correlation channels, involve hole-pair operators that are spin singlets, use nearest-neighbor sites, and employ different orbitals for each hole. As a result, the Hund coupling strength, presence of robust magnetic moments, and antiferromagnetic correlations among them are important for the binding tendencies found here.

Magnetic properties of three-dimensional Hubbard-sigma model

International Nuclear Information System (INIS)

Yamamoto, Hisashi; Ichinose, Ikuo; Tatara, Gen; Matsui, Tetsuo.

1989-11-01

It is broadly viewed that the magnetism may play an important role in the high-T c superconductivity in the lamellar CuO 2 materials. In this paper, based on a Hubbard-inspired CP 1 or S 2 nonlinear σ model, we give a quantitative study of some magnetic properties in and around the Neel ordered state of three-dimensional quantum antiferromagnets such as La 2 CuO 4 with and without small hole doping. Our model is a (3+1) dimensional effective field theory describing the low energy spin dynamics of a three-dimensional Hubbard model with a very weak interlayer coupling. The effect of hole dynamics is taken into account in the leading approximation by substituting the CP 1 coupling with an 'effective' one determined by the concentration and the one-loop correction of hole fermions. A stationary-phase equation for the one-loop effective potential of S 2 model is analyzed numerically. The behavior of Neel temperature, magnetization (long range Neel order), spin correlation length, etc as functions of anisotropic parameter, temperature, hole concentrations, etc are investigated in detail. A phase diagram is also supported by the renormlization group analysis. The results show that our anisotropic field theory model with certain values of parameters could give a reasonably well description of the magnetic properties indicated by some experiments on pure and doped La 2 CuO 4 . (author)

Ground state phase diagram of extended attractive Hubbard model

International Nuclear Information System (INIS)

Robaszkiewicz, S.; Chao, K.A.; Micnas, R.

1980-08-01

The ground state phase diagram of the extended Hubbard model with intraatomic attraction has been derived in the Hartree-Fock approximation formulated in terms of the Bogoliubov variational approach. For a given value of electron density, the nature of the ordered ground state depends essentially on the sign and the strength of the nearest neighbor coupling. (author)

Behaviour of the energy gap in a model of Josephson coupled Bose-Einstein condensates

International Nuclear Information System (INIS)

Tonel, A P; Links, J; Foerster, A

2005-01-01

In this work we investigate the energy gap between the ground state and the first excited state in a model of two single-mode Bose-Einstein condensates coupled via Josephson tunnelling. The energy gap is never zero when the tunnelling interaction is non-zero. The gap exhibits no local minimum below a threshold coupling which separates a delocalized phase from a self-trapping phase that occurs in the absence of the external potential. Above this threshold point one minimum occurs close to the Josephson regime, and a set of minima and maxima appear in the Fock regime. Expressions for the position of these minima and maxima are obtained. The connection between these minima and maxima and the dynamics for the expectation value of the relative number of particles is analysed in detail. We find that the dynamics of the system changes as the coupling crosses these points

Bright solitons in coupled defocusing NLS equation supported by coupling: Application to Bose-Einstein condensation

International Nuclear Information System (INIS)

Adhikari, Sadhan K.

2005-01-01

We demonstrate the formation of bright solitons in coupled self-defocusing nonlinear Schroedinger (NLS) equation supported by attractive coupling. As an application we use a time-dependent dynamical mean-field model to study the formation of stable bright solitons in two-component repulsive Bose-Einstein condensates (BECs) supported by interspecies attraction in a quasi one-dimensional geometry. When all interactions are repulsive, there cannot be bright solitons. However, bright solitons can be formed in two-component repulsive BECs for a sufficiently attractive interspecies interaction, which induces an attractive effective interaction among bosons of same type

Phase competition in a one-dimensional three-orbital Hubbard-Holstein model

Science.gov (United States)

Li, Shaozhi; Tang, Yanfei; Maier, Thomas A.; Johnston, Steven

2018-05-01

We study the interplay between the electron-phonon (e -ph) and on-site electron-electron (e-e) interactions in a three-orbital Hubbard-Holstein model on an extended one-dimensional lattice using determinant quantum Monte Carlo. For weak e-e and e -ph interactions, we observe a competition between an orbital-selective Mott phase (OSMP) and a (multicomponent) charge-density-wave (CDW) insulating phase, with an intermediate metallic phase located between them. For large e-e and e -ph couplings, the OSMP and CDW phases persist, while the metallic phase develops short-range orbital correlations and becomes insulating when both the e-e and e -ph interactions are large but comparable. Many of our conclusions are in line with those drawn from a prior dynamical mean-field theory study of the two-orbital Hubbard-Holstein model [Phys. Rev. B 95, 121112(R) (2017), 10.1103/PhysRevB.95.121112] in infinite dimension, suggesting that the competition between the e -ph and e-e interactions in multiorbital Hubbard-Holstein models leads to rich physics, regardless of the dimension of the system.

The MFA ground states for the extended Bose-Hubbard model with a three-body constraint

Science.gov (United States)

Panov, Yu. D.; Moskvin, A. S.; Vasinovich, E. V.; Konev, V. V.

2018-05-01

We address the intensively studied extended bosonic Hubbard model (EBHM) with truncation of the on-site Hilbert space to the three lowest occupation states n = 0 , 1 , 2 in frames of the S = 1 pseudospin formalism. Similar model was recently proposed to describe the charge degree of freedom in a model high-T c cuprate with the on-site Hilbert space reduced to the three effective valence centers, nominally Cu1+;2+;3+. With small corrections the model becomes equivalent to a strongly anisotropic S = 1 quantum magnet in an external magnetic field. We have applied a generalized mean-field approach and quantum Monte-Carlo technique for the model 2D S = 1 system with a two-particle transport to find the ground state phase with its evolution under deviation from half-filling.

Thermalization after an interaction quench in the Hubbard model.

Science.gov (United States)

Eckstein, Martin; Kollar, Marcus; Werner, Philipp

2009-07-31

We use nonequilibrium dynamical mean-field theory to study the time evolution of the fermionic Hubbard model after an interaction quench. Both in the weak-coupling and in the strong-coupling regime the system is trapped in quasistationary states on intermediate time scales. These two regimes are separated by a sharp crossover at U(c)dyn=0.8 in units of the bandwidth, where fast thermalization occurs. Our results indicate a dynamical phase transition which should be observable in experiments on trapped fermionic atoms.

Penson-Kolb-Hubbard model: a renormalisation group study

International Nuclear Information System (INIS)

Bhattacharyya, Bibhas; Roy, G.K.

1995-01-01

The Penson-Kolb-Hubbard (PKH) model in one dimension (1d) by means of real space renormalisation group (RG) method for the half-filled band has been studied. Different phases are identified by studying the RG-flow pattern, the energy gap and different correlation functions. The phase diagram consists of four phases: a spin density wave (SDW), a strong coupling superconducting phase (SSC), a weak coupling superconducting phase (WSC) and a nearly metallic phase. For the negative value of the pair hopping amplitude introduced in this model it was found that the pair-pair correlation indicates a superconducting phase for which the centre-of-mass of the pairs move with a momentum π. (author). 7 refs., 4 figs

Universal quantum computation by scattering in the Fermi–Hubbard model

International Nuclear Information System (INIS)

Bao, Ning; Hayden, Patrick; Salton, Grant; Thomas, Nathaniel

2015-01-01

The Hubbard model may be the simplest model of particles interacting on a lattice, but simulation of its dynamics remains beyond the reach of current numerical methods. In this article, we show that general quantum computations can be encoded into the physics of wave packets propagating through a planar graph, with scattering interactions governed by the fermionic Hubbard model. Therefore, simulating the model on planar graphs is as hard as simulating quantum computation. We give two different arguments, demonstrating that the simulation is difficult both for wave packets prepared as excitations of the fermionic vacuum, and for hole wave packets at filling fraction one-half in the limit of strong coupling. In the latter case, which is described by the t-J model, there is only reflection and no transmission in the scattering events, as would be the case for classical hard spheres. In that sense, the construction provides a quantum mechanical analog of the Fredkin–Toffoli billiard ball computer. (paper)

Collective excitations in the Penson-Kolb model: A generalized random-phase-approximation study

International Nuclear Information System (INIS)

Roy, G.K.; Bhattacharyya, B.

1997-01-01

The evolution of the superconducting ground state of the half-filled Penson-Kolb model is examined as a function of the coupling constant using a mean-field approach and the generalized random phase approximation (RPA) in two and three dimensions. On-site singlet pairs hop to compete against single-particle motion in this model, giving the coupling constant a strong momentum dependence. There is a pronounced bandwidth enhancement effect that converges smoothly to a finite value in the strong-coupling (Bose) regime. The low-lying collective excitations evaluated in generalized RPA show a linear dispersion and a gradual crossover from the weak-coupling (BCS) limit to the Bose regime; the mode velocity increases monotonically in sharp contrast to the attractive Hubbard model. Analytical results are derived in the asymptotic limits. copyright 1997 The American Physical Society

A Riemann-Hilbert formulation for the finite temperature Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Cavaglià, Andrea [Dipartimento di Fisica and INFN, Università di Torino,Via P. Giuria 1, 10125 Torino (Italy); Cornagliotto, Martina [Dipartimento di Fisica and INFN, Università di Torino,Via P. Giuria 1, 10125 Torino (Italy); DESY Hamburg, Theory Group,Notkestrasse 85, D-22607 Hamburg (Germany); Mattelliano, Massimo; Tateo, Roberto [Dipartimento di Fisica and INFN, Università di Torino,Via P. Giuria 1, 10125 Torino (Italy)

2015-06-03

Inspired by recent results in the context of AdS/CFT integrability, we reconsider the Thermodynamic Bethe Ansatz equations describing the 1D fermionic Hubbard model at finite temperature. We prove that the infinite set of TBA equations are equivalent to a simple nonlinear Riemann-Hilbert problem for a finite number of unknown functions. The latter can be transformed into a set of three coupled nonlinear integral equations defined over a finite support, which can be easily solved numerically. We discuss the emergence of an exact Bethe Ansatz and the link between the TBA approach and the results by Jüttner, Klümper and Suzuki based on the Quantum Transfer Matrix method. We also comment on the analytic continuation mechanism leading to excited states and on the mirror equations describing the finite-size Hubbard model with twisted boundary conditions.

Moment approach for the attractive Hubbard model in two dimensions: superconductivity

Energy Technology Data Exchange (ETDEWEB)

Rodriguez-Nunez, J.J.; Cordeiro, C.; Delfino, A. [Universidade Federal Fluminense, Niteroi, RJ (Brazil). Inst. de Fisica

1997-12-31

Full text. Using the moment of Nolting (Z. Phys. 225, 25 (1972) for the attractive Hubbard model in the superconducting phase, we have derived a set of three non-linear equations, the electron density, the superconducting order parameter, and the narrowing factor. Our starting point is the Ansatz that the diagonal spectral density is composed of three peaks while the off-diagonal spectral functional is composed of two. The third band, or upper Hubbard band, strongly renormalizes the other two, making the energy gap K dependent while the order parameter is pure s-wave. Our approach recuperates the BCS limit, weak coupling (U/t <<1) in a natural way. We solve these non-linear equations in a self-consistent way for intermediate coupling for U/t {approx} -4.0. Here we report the order parameter as function of temperature and compare it with the BCS result. (author)

A quasi-exactly solvable Lipkin-Meshkov-Glick model

International Nuclear Information System (INIS)

Pan Feng; Lin Jijie; Xue Xiaogang; Draayer, J P

2010-01-01

We prove that a special Lipkin-Meshkov-Glick model is quasi-exactly solvable with solutions that can be expressed in the SU(2) coherent state form. Ground-state properties of the model are studied analytically. We also show that the model reduces to the standard two-site Bose-Hubbard model in the large-N limit for finite U/t or large (N - 1)|U|/t cases with finite N, which proves that in these cases the ground state of the standard two-site Bose-Hubbard model is an SU(2) coherent state.

Functional renormalization for antiferromagnetism and superconductivity in the Hubbard model

International Nuclear Information System (INIS)

Friederich, Simon

2010-01-01

Despite its apparent simplicity, the two-dimensional Hubbard model for locally interacting fermions on a square lattice is widely considered as a promising approach for the understanding of Cooper pair formation in the quasi two-dimensional high-T c cuprate materials. In the present work this model is investigated by means of the functional renormalization group, based on an exact flow equation for the effective average action. In addition to the fermionic degrees of freedom of the Hubbard Hamiltonian, bosonic fields are introduced which correspond to the different possible collective orders of the system, for example magnetism and superconductivity. The interactions between bosons and fermions are determined by means of the method of ''rebosonization'' (or ''flowing bosonization''), which can be described as a continuous, scale-dependent Hubbard-Stratonovich transformation. This method allows an efficient parameterization of the momentum-dependent effective two-particle interaction between fermions (four-point vertex), and it makes it possible to follow the flow of the running couplings into the regimes exhibiting spontaneous symmetry breaking, where bosonic fluctuations determine the types of order which are present on large length scales. Numerical results for the phase diagram are presented, which include the mutual influence of different, competing types of order. (orig.)

Functional renormalization for antiferromagnetism and superconductivity in the Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Friederich, Simon

2010-12-08

Despite its apparent simplicity, the two-dimensional Hubbard model for locally interacting fermions on a square lattice is widely considered as a promising approach for the understanding of Cooper pair formation in the quasi two-dimensional high-T{sub c} cuprate materials. In the present work this model is investigated by means of the functional renormalization group, based on an exact flow equation for the effective average action. In addition to the fermionic degrees of freedom of the Hubbard Hamiltonian, bosonic fields are introduced which correspond to the different possible collective orders of the system, for example magnetism and superconductivity. The interactions between bosons and fermions are determined by means of the method of ''rebosonization'' (or ''flowing bosonization''), which can be described as a continuous, scale-dependent Hubbard-Stratonovich transformation. This method allows an efficient parameterization of the momentum-dependent effective two-particle interaction between fermions (four-point vertex), and it makes it possible to follow the flow of the running couplings into the regimes exhibiting spontaneous symmetry breaking, where bosonic fluctuations determine the types of order which are present on large length scales. Numerical results for the phase diagram are presented, which include the mutual influence of different, competing types of order. (orig.)

Generalized N-coupled maps with invariant measure in Bose ...

Indian Academy of Sciences (India)

Algebraic properties of the Bose-Mesner algebra with an associated scheme with definite spectrum has been used in order to study the stability of the coupled map lattice. Associated schemes play a key role and may lead to analytical methods in studying the stability of the dynamical systems. The relation between the ...

Hubbard physics in the symmetric half-filled periodic anderson-hubbard model

Science.gov (United States)

Hagymási, I.; Itai, K.; Sólyom, J.

2013-05-01

Two very different methods — exact diagonalization on finite chains and a variational method — are used to study the possibility of a metal-insulator transition in the symmetric half-filled periodic Anderson-Hubbard model. With this aim we calculate the density of doubly occupied d sites ( gn d ) as a function of various parameters. In the absence of on-site Coulomb interaction ( U f ) between f electrons, the two methods yield similar results. The double occupancy of d levels remains always finite just as in the one-dimensional Hubbard model. Exact diagonalization on finite chains gives the same result for finite U f , while the Gutzwiller method leads to a Brinkman-Rice transition at a critical value ( U {/d c }), which depends on U f and V.

Critical temperature of Bose-Einstein condensation in trapped atomic Bose-Fermi mixtures

Energy Technology Data Exchange (ETDEWEB)

Albus, A P [Institut fuer Physik, Universitaet Potsdam, D-14469 Potsdam (Germany); Giorgini, S [Dipartimento di Fisica, Universita di Trento, and Istituto Nazionale per la Fisica della Materia, I-38050 Povo (Italy); Illuminati, F [Dipartimento di Fisica, Universita di Salerno, and Istituto Nazionale per la Fisica della Materia, I-84081 Baronissi (Italy); Viverit, L [Dipartimento di Fisica, Universita di Trento, and Istituto Nazionale per la Fisica della Materia, I-38050 Povo (Italy)

2002-12-14

We calculate the shift in the critical temperature of Bose-Einstein condensation for a dilute Bose-Fermi mixture confined by a harmonic potential, to lowest order in both the Bose-Bose and Bose-Fermi coupling constants. The relative importance of the effect on the critical temperature of the boson-boson and boson-fermion interactions is investigated as a function of the parameters of the mixture. The possible relevance of the shift of the transition temperature in current experiments on trapped Bose-Fermi mixtures is discussed. (letter to the editor)

Critical temperature of Bose-Einstein condensation in trapped atomic Bose-Fermi mixtures

International Nuclear Information System (INIS)

Albus, A P; Giorgini, S; Illuminati, F; Viverit, L

2002-01-01

We calculate the shift in the critical temperature of Bose-Einstein condensation for a dilute Bose-Fermi mixture confined by a harmonic potential, to lowest order in both the Bose-Bose and Bose-Fermi coupling constants. The relative importance of the effect on the critical temperature of the boson-boson and boson-fermion interactions is investigated as a function of the parameters of the mixture. The possible relevance of the shift of the transition temperature in current experiments on trapped Bose-Fermi mixtures is discussed. (letter to the editor)

Single-particle spectral density of the Hubbard model

NARCIS (Netherlands)

Mehlig, B.; Eskes, H.; Hayn, R.; Meinders, M.B.J.

1995-01-01

We calculate the single-particle spectral function for the Hubbard model within the framework of a projection technique equivalent to the two-pole approximation. We show that the two-pole approximation can be well understood as an average characterization of the upper and the lower Hubbard bands,

SINGLE-PARTICLE SPECTRAL DENSITY OF THE HUBBARD-MODEL

NARCIS (Netherlands)

MEHLIG, B; ESKES, H; HAYN, R; MEINDERS, MBJ

1995-01-01

We calculate the single-particle spectral function for the Hubbard model within the framework of a projection technique equivalent to the two-pole approximation. We show that the two-pole approximation can be well understood as an average characterization of the upper and the lower Hubbard bands,

On the number of Bose-selected modes in driven-dissipative ideal Bose gases

Science.gov (United States)

Schnell, Alexander; Ketzmerick, Roland; Eckardt, André

2018-03-01

In an ideal Bose gas that is driven into a steady state far from thermal equilibrium, a generalized form of Bose condensation can occur. Namely, the single-particle states unambiguously separate into two groups: the group of Bose-selected states, whose occupations increase linearly with the total particle number, and the group of all other states whose occupations saturate [Phys. Rev. Lett. 111, 240405 (2013), 10.1103/PhysRevLett.111.240405]. However, so far very little is known about how the number of Bose-selected states depends on the properties of the system and its coupling to the environment. The answer to this question is crucial since systems hosting a single, a few, or an extensive number of Bose-selected states will show rather different behavior. While in the former two scenarios each selected mode acquires a macroscopic occupation, corresponding to (fragmented) Bose condensation, the latter case rather bears resemblance to a high-temperature state of matter. In this paper, we systematically investigate the number of Bose-selected states, considering different classes of the rate matrices that characterize the driven-dissipative ideal Bose gases in the limit of weak system-bath coupling. These include rate matrices with continuum limit, rate matrices of chaotic driven systems, random rate matrices, and rate matrices resulting from thermal baths that couple to a few observables only.

Magnetic properties of Hubbard-sigma model with three-dimensionality

International Nuclear Information System (INIS)

Yamamoto, Hisashi; Tatara, Gen; Ichinose, Ikuo; Matsui, Tetsuo.

1990-05-01

It has been broadly accepted that the magnetism may play an important role in the high-T c superconductivity in the lamellar CuO 2 materials. In this paper, based on a Hubbard-inspired CP 1 or S 2 nonlinear σ model, we give a quantitative study of some magnetic properties in and around the Neel ordered state of three-dimensional quantum antiferromagnets such as La 2 CuO 4 with and without small hole doping. Our model is a (3+1) dimensional effective field theory describing the low energy spin dynamics of a three-dimensional Hubbard model with a very weak interlayer coupling. The effect of hole dynamics is taken into account in the leading approximation by substituting the CP 1 coupling and the spin-wave velocity with 'effective' ones determined by the concentration and the one-loop correction of hole fermions. Stationary-phase equations for the one-loop effective potential of S 2 model are analyzed. Based on them, various magnetic properties of the system, such as the behavior of Neel temperature, spin correlation length, staggered magnetization, specific heat and susceptibility as functions of anisotropic parameter, temperature, etc. are investigated in detail. The results show that our anisotropic field theory model with certain values of parameters gives a good description of the magnetic properties in both the ordered and the disordered phases indicated by experiments on La 2 CuO 4 . The part of the above results is supported by the renormalization-group analysis. In the doped case it is observed that the existence of holes destroys the long-range order and their hopping effect is large. (author)

Enhanced pairing susceptibility in a photodoped two-orbital Hubbard model

Science.gov (United States)

Werner, Philipp; Strand, Hugo U. R.; Hoshino, Shintaro; Murakami, Yuta; Eckstein, Martin

2018-04-01

Local spin fluctuations provide the glue for orbital-singlet spin-triplet pairing in the doped Mott insulating regime of multiorbital Hubbard models. At large Hubbard repulsion U , the pairing susceptibility is nevertheless tiny because the pairing interaction cannot overcome the suppression of charge fluctuations. Using nonequilibrium dynamical mean field simulations of the two-orbital Hubbard model, we show that out of equilibrium the pairing susceptibility in this large-U regime can be strongly enhanced by creating a photoinduced population of the relevant charge states. This enhancement is supported by the long lifetime of photodoped charge carriers and a built-in cooling mechanism in multiorbital Hubbard systems.

Single-particle properties of the Hubbard model in a novel three-pole approximation

Science.gov (United States)

Di Ciolo, Andrea; Avella, Adolfo

2018-05-01

We study the 2D Hubbard model using the Composite Operator Method within a novel three-pole approximation. Motivated by the long-standing experimental puzzle of the single-particle properties of the underdoped cuprates, we include in the operatorial basis, together with the usual Hubbard operators, a field describing the electronic transitions dressed by the nearest-neighbor spin fluctuations, which play a crucial role in the unconventional behavior of the Fermi surface and of the electronic dispersion. Then, we adopt this approximation to study the single-particle properties in the strong coupling regime and find an unexpected behavior of the van Hove singularity that can be seen as a precursor of a pseudogap regime.

Competition between spin, charge, and bond waves in a Peierls-Hubbard model

International Nuclear Information System (INIS)

Venegas, P.A.; Henriquez, C.; Roessler, J.

1996-01-01

We study a one-dimensional extended Peierls-Hubbard model coupled to intracell and intercell phonons for a half-filled band. The calculations are made using the Hartree-Fock and adiabatic approximations for arbitrary temperature. In addition to static spin, charge, and bond density waves, we predict intermediate phases that lack inversion symmetry, and phase transitions that reduce symmetry on increasing temperature. copyright 1996 The American Physical Society

Unsupervised machine learning account of magnetic transitions in the Hubbard model

Science.gov (United States)

Ch'ng, Kelvin; Vazquez, Nick; Khatami, Ehsan

2018-01-01

We employ several unsupervised machine learning techniques, including autoencoders, random trees embedding, and t -distributed stochastic neighboring ensemble (t -SNE), to reduce the dimensionality of, and therefore classify, raw (auxiliary) spin configurations generated, through Monte Carlo simulations of small clusters, for the Ising and Fermi-Hubbard models at finite temperatures. Results from a convolutional autoencoder for the three-dimensional Ising model can be shown to produce the magnetization and the susceptibility as a function of temperature with a high degree of accuracy. Quantum fluctuations distort this picture and prevent us from making such connections between the output of the autoencoder and physical observables for the Hubbard model. However, we are able to define an indicator based on the output of the t -SNE algorithm that shows a near perfect agreement with the antiferromagnetic structure factor of the model in two and three spatial dimensions in the weak-coupling regime. t -SNE also predicts a transition to the canted antiferromagnetic phase for the three-dimensional model when a strong magnetic field is present. We show that these techniques cannot be expected to work away from half filling when the "sign problem" in quantum Monte Carlo simulations is present.

Spin-orbit-coupled Bose-Einstein condensates of rotating polar molecules

Science.gov (United States)

Deng, Y.; You, L.; Yi, S.

2018-05-01

An experimental proposal for realizing spin-orbit (SO) coupling of pseudospin 1 in the ground manifold 1Σ (υ =0 ) of (bosonic) bialkali polar molecules is presented. The three spin components are composed of the ground rotational state and two substates from the first excited rotational level. Using hyperfine resolved Raman processes through two select excited states resonantly coupled by a microwave, an effective coupling between the spin tensor and linear momentum is realized. The properties of Bose-Einstein condensates for such SO-coupled molecules exhibiting dipolar interactions are further explored. In addition to the SO-coupling-induced stripe structures, the singly and doubly quantized vortex phases are found to appear, implicating exciting opportunities for exploring novel quantum physics using SO-coupled rotating polar molecules with dipolar interactions.

Fourier-accelerated Langevin simulation of the frustrated XY model and simulation of the spinless and spin one-half Hubbard model

International Nuclear Information System (INIS)

Scheinine, A.L.

1992-01-01

The frustrated XY model was studied on a lattice, primarily to test Fourier transform acceleration technique for a phase transition having more field structure than just spinwaves and vortices. Also, the spinless Hubbard model without hopping was simulated using continuous variables for the auxiliary field that mediates coupling between fermions. Finally, spin one-half Hubbard model was studied with a technique that sampled the fermion occupation configurations. The frustrated two-dimensional XY model was simulated using the Langevin equation with Fourier transform acceleration. Speedup due to Fourier acceleration was measured for frustration one-half at the transition temperature. The unfrustrated XY model was also studied. For the frustrated case, only long-distance spin correlation and the autocorrelation of the spin showed significant speedup. The frustrated case has Ising-like domains. It was found that Fourier acceleration speeds the evolution of spinwaves but has negligible effect on the Ising-like domains. In the Hubbard model, fermion determinant weight factor in the partition function changes sign, causing large statistical fluctuations of observables. A technique was found for sampling configuration space using continuous auxiliary fields, despite energy barriers where the fermion determinant changes sign. For two-dimensional spinless Hubbard model with no hopping, an exact solution was found for a 4 x 4 lattice; which could be compared to numerical simulations. The sign problem remained, and was found to be related to the sign problem encountered when a discrete variable is used for the auxiliary field. For spin one-half Hubbard model, a Monte Carlo simulation was done in which the fermion occupation configurations were varied. Rather than integrate-out the fermions and make a numerical estimate of the sum over the auxiliary field, the auxiliary field was integrated-out and a numerical estimate was made of the sum over fermion configurations

Physical replicas and the Bose glass in cold atomic gases

International Nuclear Information System (INIS)

Morrison, S; Kantian, A; Daley, A J; Zoller, P; Katzgraber, H G; Lewenstein, M; Buechler, H P

2008-01-01

We study cold atomic gases in a disorder potential and analyse the correlations between different systems subjected to the same disorder landscape. Such independent copies with the same disorder landscape are known as replicas. While, in general, these are not accessible experimentally in condensed matter systems, they can be realized using standard tools for controlling cold atomic gases in an optical lattice. Of special interest is the overlap function which represents a natural order parameter for disordered systems and is a correlation function between the atoms of two independent replicas with the same disorder. We demonstrate an efficient measurement scheme for the determination of this disorder-induced correlation function. As an application, we focus on the disordered Bose-Hubbard model and determine the overlap function within the perturbation theory and a numerical analysis. We find that the measurement of the overlap function allows for the identification of the Bose-glass phase in certain parameter regimes

Physical replicas and the Bose glass in cold atomic gases

Energy Technology Data Exchange (ETDEWEB)

Morrison, S; Kantian, A; Daley, A J; Zoller, P [Institute for Theoretical Physics, University of Innsbruck, Technikerstr. 25, A-6020 Innsbruck (Austria); Katzgraber, H G [Theoretische Physik, ETH Zurich, CH-8093 Zuerich (Switzerland); Lewenstein, M [ICAO-Institut de Ciencies Fotoniques, Parc Mediterrani de la Tecnologia, E-08860 Castelldefels, Barcelona (Spain); Buechler, H P [Institute for Theoretical Physics III, University of Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany)], E-mail: sarah.morrison@uibk.ac.at

2008-07-15

We study cold atomic gases in a disorder potential and analyse the correlations between different systems subjected to the same disorder landscape. Such independent copies with the same disorder landscape are known as replicas. While, in general, these are not accessible experimentally in condensed matter systems, they can be realized using standard tools for controlling cold atomic gases in an optical lattice. Of special interest is the overlap function which represents a natural order parameter for disordered systems and is a correlation function between the atoms of two independent replicas with the same disorder. We demonstrate an efficient measurement scheme for the determination of this disorder-induced correlation function. As an application, we focus on the disordered Bose-Hubbard model and determine the overlap function within the perturbation theory and a numerical analysis. We find that the measurement of the overlap function allows for the identification of the Bose-glass phase in certain parameter regimes.

Dark matter as a Bose-Einstein Condensate: the relativistic non-minimally coupled case

International Nuclear Information System (INIS)

Bettoni, Dario; Colombo, Mattia; Liberati, Stefano

2014-01-01

Bose-Einstein Condensates have been recently proposed as dark matter candidates. In order to characterize the phenomenology associated to such models, we extend previous investigations by studying the general case of a relativistic BEC on a curved background including a non-minimal coupling to curvature. In particular, we discuss the possibility of a two phase cosmological evolution: a cold dark matter-like phase at the large scales/early times and a condensed phase inside dark matter halos. During the first phase dark matter is described by a minimally coupled weakly self-interacting scalar field, while in the second one dark matter condensates and, we shall argue, develops as a consequence the non-minimal coupling. Finally, we discuss how such non-minimal coupling could provide a new mechanism to address cold dark matter paradigm issues at galactic scales

Alternating chain with Hubbard-type interactions: renormalization group analysis

International Nuclear Information System (INIS)

Buzatu, F. D.; Jackeli, G.

1998-01-01

A large amount of work has been devoted to the study of alternating chains for a better understanding of the high-T c superconductivity mechanism. The same phenomenon renewed the interest in the Hubbard model and in its one-dimensional extensions. In this work we investigate, using the Renormalization Group (RG) method, the effect of the Hubbard-type interactions on the ground-state properties of a chain with alternating on-site atomic energies. The one-particle Hamiltonian in the tight binding approximation corresponding to an alternating chain with two nonequivalent sites per unit cell can be diagonalized by a canonical transformation; one gets a two band model. The Hubbard-type interactions give rise to both intra- and inter-band couplings; however, if the gap between the two bands is sufficiently large and the system is more than half-filled, as for the CuO 3 chain occurring in high-T c superconductors, the last ones can be neglected in describing the low energy physics. We restrict our considerations to the Hubbard-type interactions (upper band) in the particular case of alternating on-site energies and equal hopping amplitudes. The standard RG analysis (second order) is done in terms of the g-constants describing the elementary processes of forward, backward and Umklapp scatterings: their expressions are obtained by evaluating the Hubbard-type interactions (upper band) at the Fermi points. Using the scaling to the exact soluble models Tomonaga-Luttinger and Luther-Emery, we can predict the low energy physics of our system. The ground-state phase diagrams in terms of the model parameters and at arbitrary band filling are determined, where four types of instabilities have been considered: Charge Density Waves (CDW), Spin Density Waves (SDW), Singlet Superconductivity (SS) and Triplet Superconductivity (TS). The 3/4-filled case in terms of some renormalized Hubbard constants is presented. The relevance of our analysis to the case of the undistorted 3/4-filled Cu

Effect of Inhomogeneity on s-wave Superconductivity in the Attractive Hubbard Model

Energy Technology Data Exchange (ETDEWEB)

Aryanpour, K. A. [University of California, Davis; Dagotto, Elbio R [ORNL; Mayr, Matthias [Max-Planck-Institut fur Feskorperforschung, Stuttgart, Germany; Paiva, T. [Universidade Federal do Rio de Janeiro, Brazil; Pickett, W. E. [University of California, Davis; Scalettar, Richard T [ORNL

2006-01-01

Inhomogeneous s-wave superconductivity is studied in the two-dimensional, square lattice attractive Hubbard Hamiltonian using the Bogoliubov-de Gennes BdG mean field approximation. We find that at weak coupling, and for densities mainly below half-filling, an inhomogeneous interaction in which the on-site interaction Ui takes on two values, Ui=0, 2U results in a larger zero temperature pairing amplitude, and that the superconducting Tc can also be significantly increased, relative to a uniform system with Ui=U on all sites. These effects are observed for stripe, checkerboard, and even random patterns of the attractive centers, suggesting that the pattern of inhomogeneity is unimportant. Monte Carlo calculations which reintroduce some of the fluctuations neglected within the BdG approach see the same effect, both for the attractive Hubbard model and a Hamiltonian with d-wave pairing symmetry.

Spin-spin correlations in the tt'-Hubbard model

International Nuclear Information System (INIS)

Husslein, T.; Newns, D.M.; Mattutis, H.G.; Pattnaik, P.C.; Morgenstern, I.; Singer, J.M.; Fettes, W.; Baur, C.

1994-01-01

We present calculations of the tt'-Hubbard model using Quantum Monte Carlo techniques. The parameters are chosen so that the van Hove Singularity in the density of states and the Fermi level coincide. We study the behaviour of the system with increasing Hubbard interaction U. Special emphasis is on the spin-spin correlation (SSC). Unusual behaviour for large U is observed there and in the momentum distribution function (n(q)). (orig.)

Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array

Science.gov (United States)

Hensgens, T.; Fujita, T.; Janssen, L.; Li, Xiao; van Diepen, C. J.; Reichl, C.; Wegscheider, W.; Das Sarma, S.; Vandersypen, L. M. K.

2017-08-01

Interacting fermions on a lattice can develop strong quantum correlations, which are the cause of the classical intractability of many exotic phases of matter. Current efforts are directed towards the control of artificial quantum systems that can be made to emulate the underlying Fermi-Hubbard models. Electrostatically confined conduction-band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical initialization of low-entropy states and readily adhere to the Fermi-Hubbard Hamiltonian. Until now, however, the substantial electrostatic disorder of the solid state has meant that only a few attempts at emulating Fermi-Hubbard physics on solid-state platforms have been made. Here we show that for gate-defined quantum dots this disorder can be suppressed in a controlled manner. Using a semi-automated and scalable set of experimental tools, we homogeneously and independently set up the electron filling and nearest-neighbour tunnel coupling in a semiconductor quantum dot array so as to simulate a Fermi-Hubbard system. With this set-up, we realize a detailed characterization of the collective Coulomb blockade transition, which is the finite-size analogue of the interaction-driven Mott metal-to-insulator transition. As automation and device fabrication of semiconductor quantum dots continue to improve, the ideas presented here will enable the investigation of the physics of ever more complex many-body states using quantum dots.

Quantum simulation of a Fermi-Hubbard model using a semiconductor quantum dot array.

Science.gov (United States)

Hensgens, T; Fujita, T; Janssen, L; Li, Xiao; Van Diepen, C J; Reichl, C; Wegscheider, W; Das Sarma, S; Vandersypen, L M K

2017-08-02

Interacting fermions on a lattice can develop strong quantum correlations, which are the cause of the classical intractability of many exotic phases of matter. Current efforts are directed towards the control of artificial quantum systems that can be made to emulate the underlying Fermi-Hubbard models. Electrostatically confined conduction-band electrons define interacting quantum coherent spin and charge degrees of freedom that allow all-electrical initialization of low-entropy states and readily adhere to the Fermi-Hubbard Hamiltonian. Until now, however, the substantial electrostatic disorder of the solid state has meant that only a few attempts at emulating Fermi-Hubbard physics on solid-state platforms have been made. Here we show that for gate-defined quantum dots this disorder can be suppressed in a controlled manner. Using a semi-automated and scalable set of experimental tools, we homogeneously and independently set up the electron filling and nearest-neighbour tunnel coupling in a semiconductor quantum dot array so as to simulate a Fermi-Hubbard system. With this set-up, we realize a detailed characterization of the collective Coulomb blockade transition, which is the finite-size analogue of the interaction-driven Mott metal-to-insulator transition. As automation and device fabrication of semiconductor quantum dots continue to improve, the ideas presented here will enable the investigation of the physics of ever more complex many-body states using quantum dots.

Phase transitions in the Hubbard Hamiltonian

International Nuclear Information System (INIS)

Chaves, C.M.; Lederer, P.; Gomes, A.A.

1977-05-01

Phase transition in the isotropic non-degenerate Hubbard Hamiltonian within the renormalization group techniques is studied, using the epsilon = 4 - d expansion to first order in epsilon. The functional obtained from the Hubbard Hamiltonian displays full rotation symmetry and describes two coupled fields: a vector spin field, with n components and a non-soft scalar charge field. This coupling is pure imaginary, which has interesting consequences on the critical properties of this coupled field system. The effect of simple constraints imposed on the charge field is considered. The relevance of the coupling between the fields in producing Fisher renormalization of the critical exponents is discussed. The possible singularities introduced in the charge-charge correlation function by the coupling are also discussed

Quantum Simulation of the Hubbard Model Using Ultra-Cold Atoms

Science.gov (United States)

2008-11-01

Hubbard model. The SU(3) Hubbard model has been proposed as a model system for studying different phases of matter expected to occur in quantum...chromodynamics (QCD): the color superconducting phase and the formation of baryons . Our initial investigations have focused on understanding three-body...density quark matter described by quantum chromodynamics . We have been investigating the stability of the 3-state Fermi gas with respect to decay due

Antiferromagnetism and d-wave superconductivity in the Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Krahl, H.C.

2007-07-25

The two-dimensional Hubbard model is a promising effective model for the electronic degrees of freedom in the copper-oxide planes of high temperature superconductors. We present a functional renormalization group approach to this model with focus on antiferromagnetism and d-wave superconductivity. In order to make the relevant degrees of freedom more explicitly accessible on all length scales, we introduce composite bosonic fields mediating the interaction between the fermions. Spontaneous symmetry breaking is reflected in a non-vanishing expectation value of a bosonic field. The emergence of a coupling in the d-wave pairing channel triggered by spin wave fluctuations is demonstrated. Furthermore, the highest temperature at which the interaction strength for the electrons diverges in the renormalization flow is calculated for both antiferromagnetism and d-wave superconductivity over a wide range of doping. This ''pseudo-critical'' temperature signals the onset of local ordering. Moreover, the temperature dependence of d-wave superconducting order is studied within a simplified model characterized by a single coupling in the d-wave pairing channel. The phase transition within this model is found to be of the Kosterlitz-Thouless type. (orig.)

Charge and pairing dynamics in the attractive Hubbard model: Mode coupling and the validity of linear-response theory

Science.gov (United States)

Bünemann, Jörg; Seibold, Götz

2017-12-01

Pump-probe experiments have turned out as a powerful tool in order to study the dynamics of competing orders in a large variety of materials. The corresponding analysis of the data often relies on standard linear-response theory generalized to nonequilibrium situations. Here we examine the validity of such an approach for the charge and pairing response of systems with charge-density wave and (or) superconducting (SC) order. Our investigations are based on the attractive Hubbard model which we study within the time-dependent Hartree-Fock approximation. In particular, we calculate the quench and pump-probe dynamics for SC and charge order parameters in order to analyze the frequency spectra and the coupling of the probe field to the specific excitations. Our calculations reveal that the "linear-response assumption" is justified for small to moderate nonequilibrium situations (i.e., pump pulses) in the case of a purely charge-ordered ground state. However, the pump-probe dynamics on top of a superconducting ground state is determined by phase and amplitude modes which get coupled far from the equilibrium state indicating the failure of the linear-response assumption.

Towards an understanding of the large-U Hubbard model and a theory for high-temperature superconductors

International Nuclear Information System (INIS)

Hsu, T.C.T.

1989-01-01

This thesis describes work on a large-U Hubbard model theory for high temperature superconductors. After an introduction to recent developments in the field, the author reviews experimental results. At the same time he introduces the holon-spinon model and comment on its successes and shortcomings. Using this heuristic model he then describes a holon pairing theory of superconductivity and list some experimental evidence for this interlayer coupling theory. The latter part of the thesis is devoted to projected fermion mean field theories. They are introduced by applying this theory and some recently developed computational techniques to anisotropic antiferromagnets. This scheme is shown to give quantitatively good results for the two dimensional square lattice Heisenberg AFM. The results have definite implications for a spinon theory of quantum antiferromagnets. Finally he studies flux phases and other variational prescriptions for obtaining low lying states of the Hubbard model

Resonances for coupled Bose-Einstein condensates

International Nuclear Information System (INIS)

Haroutyunyan, H.L.; Nienhuis, G.

2004-01-01

The properties of a Bose-Einstein condensate in a two-well potential can be manipulated by periodic modulation of the potential parameters. We study the effects arising from modulating the barrier height and the difference in well depth. At certain modulation frequencies the system exhibits resonances, which may show up in an enhancement of the tunneling rate between the wells. Resonances can be used to control the particle distribution over the wells. Some of the effects occurring in the two-well system also arise for a Bose-Einstein condensate in an optical lattice

Mott metal-insulator transition in the doped Hubbard-Holstein model

Science.gov (United States)

Kurdestany, Jamshid Moradi; Satpathy, S.

2017-08-01

Motivated by the current interest in the understanding of the Mott insulators away from half-filling, observed in many perovskite oxides, we study the Mott metal-insulator transition in the doped Hubbard-Holstein model using the Hartree-Fock mean field theory. The Hubbard-Holstein model is the simplest model containing both the Coulomb and the electron-lattice interactions, which are important ingredients in the physics of the perovskite oxides. In contrast to the half-filled Hubbard model, which always results in a single phase (either metallic or insulating), our results show that away from half-filling, a mixed phase of metallic and insulating regions occurs. As the dopant concentration is increased, the metallic part progressively grows in volume, until it exceeds the percolation threshold, leading to percolative conduction. This happens above a critical dopant concentration δc, which, depending on the strength of the electron-lattice interaction, can be a significant fraction of unity. This means that the material could be insulating even for a substantial amount of doping, in contrast to the expectation that doped holes would destroy the insulating behavior of the half-filled Hubbard model. While effects of fluctuation beyond the mean field remain an open question, our results provide a starting point for the understanding of the density-driven metal-insulator transition observed in many complex oxides.

Mott transition in the Hubbard model

International Nuclear Information System (INIS)

Shastry, B.S.

1992-01-01

In this article, the author discuss W. Kohn's criterion for a metal insulator transition, within the framework of a one-band Hubbard model. This and related ideas are applied to 1-dimensional Hubbard systems, and some interesting miscellaneous results discussed. The Jordan-Wigner transformation converting the two species of fermions to two species of hardcore bosons is performed in detail, and the extra phases arising from odd-even effects are explicitly derived. Bosons are shown to prefer zero flux (i.e., diamagnetism) and the corresponding happy fluxes: for the fermions identified. A curios result following from the interplay between orbital diamagnetism and spin polarization is highlighted. A spin-statistics like theorem, showing that the anticommutation relations between fermions of opposite spin are crucial to obtain the SU(2) invariance is pointed out

Vortex dynamics in coherently coupled Bose-Einstein condensates

Science.gov (United States)

Calderaro, Luca; Fetter, Alexander L.; Massignan, Pietro; Wittek, Peter

2017-02-01

In classical hydrodynamics with uniform density, vortices move with the local fluid velocity. This description is rewritten in terms of forces arising from the interaction with other vortices. Two such positive straight vortices experience a repulsive interaction and precess in a positive (anticlockwise) sense around their common centroid. A similar picture applies to vortices in a two-component, two-dimensional uniform Bose-Einstein condensate (BEC) coherently coupled through rf Rabi fields. Unlike the classical case, however, the rf Rabi coupling induces an attractive interaction and two such vortices with positive signs now rotate in the negative (clockwise) sense. Pairs of counter-rotating vortices are instead found to translate with uniform velocity perpendicular to the line joining their cores. This picture is extended to a single vortex in a two-component trapped BEC. Although two uniform vortex-free components experience familiar Rabi oscillations of particle-number difference, such behavior is absent for a vortex in one component because of the nonuniform vortex phase. Instead the coherent Rabi coupling induces a periodic vorticity transfer between the two components.

One-Particle vs. Two-Particle Crossover in Weakly Coupled Hubbard Chains and Ladders: Perturbative Renormalization Group Approach

OpenAIRE

Kishine, Jun-ichiro; Yonemitsu, Kenji

1997-01-01

Physical nature of dimensional crossovers in weakly coupled Hubbard chains and ladders has been discussed within the framework of the perturbative renormalization-group approach. The difference between these two cases originates from different universality classes which the corresponding isolated systems belong to.

Symmetry-breaking solutions of the Hubbard model

International Nuclear Information System (INIS)

Kuzemsky, A.L.; )

1998-10-01

The problem of finding the ferromagnetic and antiferromagnetic ''broken symmetry'' solutions of the correlated lattice fermion models beyond the mean-field approximation has been investigated. The calculation of the quasiparticle excitation spectrum with damping for the single- and multi-orbital Hubbard model has been performed in the framework of the equation-of-motion method for two-time temperature Green's Functions within a non-perturbative approach. A unified scheme for the construction of Generalised Mean Fields (elastic scattering corrections) and self-energy (inelastic scattering) in terms of Dyson equation has been generalised in order to include the presence of the ''source fields''. The damping of quasiparticles, which reflects the interaction of the single-particle and collective degrees of freedom has been calculated. The ''broken symmetry'' dynamical solutions of the Hubbard model, which correspond to various types of itinerant antiferromagnetism have been discussed. This approach complements previous studies and clarifies the nature of the concepts of itinerant antiferromagnetism and ''spin-aligning field'' of correlated lattice fermions. (author)

Optical conductivity of the Hubbard model

International Nuclear Information System (INIS)

Vicente Alvarez, J.J.; Balseiro, C.A.; Ceccatto, H.A.

1996-07-01

We study the response to a static electric field (charge stiffness) and the frequency-dependent conductivity of the Hubbard model in a resonant-valence-bond-type paramagnetic phase. This phase is described by means of a charge and spin rotational-invariant approach, based on a mixed fermion-boson representation of the original strongly correlated electrons. We found that the Mott transition at half filling is well described by the charge stiffness behaviour, and that the values for this quantity off half filling agree reasonably well with numerical results. Furthermore, for the frequency-dependent conductivity we trace back the origin of the band which appears inside the Hubbard gap to magnetic pair breaking. This points to a magnetic origin of midinfrared band in high-T c compounds, with no relation to superconductivity. (author). 12 refs, 2 tabs

Collapse and revival oscillations as a probe for the tunneling amplitude in an ultracold Bose gas

International Nuclear Information System (INIS)

Wolf, F. Alexander; Hen, Itay; Rigol, Marcos

2010-01-01

We present a theoretical study of the quantum corrections to the revival time due to finite tunneling in the collapse and revival of matter-wave interference after a quantum quench. We study hard-core bosons in a superlattice potential and the Bose-Hubbard model by means of exact numerical approaches and mean-field theory. We consider systems without and with a trapping potential present. We show that the quantum corrections to the revival time can be used to accurately determine the value of the hopping parameter in experiments with ultracold bosons in optical lattices.

Superconducting, magnetic, and charge correlations in the doped two-chain Hubbard model

International Nuclear Information System (INIS)

Asai, Y.

1995-01-01

We have studied the superconducting, magnetic, and charge correlation functions and the spin excitation spectrum in the doped two-chain Hubbard model by projector Monte Carlo and Lanczos diagonalization methods. The exponent of the interchain singlet superconducting correlation function, γ, is found to be close to 2.0 as long as two distinct noninteracting bands cross the Fermi level. Magnetic and charge correlation functions decay more rapidly than or as fast as the interchain singlet superconducting correlation function along the chains. The superconducting correlation in the doped two-chain Hubbard model is the most long-range correlation studied here. Implications of the results for the possible universality class of the doped two-chain Hubbard model are discussed

Exotic superconducting states in the extended attractive Hubbard model.

Science.gov (United States)

Nayak, Swagatam; Kumar, Sanjeev

2018-04-04

We show that the extended attractive Hubbard model on a square lattice allows for a variety of superconducting phases, including exotic mixed-symmetry phases with [Formula: see text] and [Formula: see text] symmetries, and a novel [Formula: see text] state. The calculations are performed within the Hartree-Fock Bardeen-Cooper-Schrieffer framework. The ground states of the mean-field Hamiltonian are obtained via a minimization scheme that relaxes the symmetry constraints on the superconducting solutions, hence allowing for a mixing of s-, p- and d-wave order parameters. The results are obtained within the assumption of uniform-density states. Our results show that extended attractive Hubbard model can serve as an effective model for investigating properties of exotic superconductors.

Quantum phase transition of light in the Rabi–Hubbard model

International Nuclear Information System (INIS)

Schiró, M; Bordyuh, M; Öztop, B; Türeci, H E

2013-01-01

We discuss the physics of the Rabi–Hubbard model describing large arrays of coupled cavities interacting with two level atoms via a Rabi nonlinearity. We show that the inclusion of counter-rotating terms in the light–matter interaction, often neglected in theoretical descriptions based on Jaynes–Cumming models, is crucial to stabilize finite-density quantum phases of correlated photons with no need for an artificially engineered chemical potential. We show that the physical properties of these phases and the quantum phase transition occurring between them is remarkably different from those of interacting bosonic massive quantum particles. The competition between photon delocalization and Rabi nonlinearity drives the system across a novel Z 2 parity symmetry-breaking quantum phase transition between two gapped phases, a Rabi insulator and a delocalized super-radiant phase. (paper)

Inverse engineering for fast transport and spin control of spin-orbit-coupled Bose-Einstein condensates in moving harmonic traps

Science.gov (United States)

Chen, Xi; Jiang, Ruan-Lei; Li, Jing; Ban, Yue; Sherman, E. Ya.

2018-01-01

We investigate fast transport and spin manipulation of tunable spin-orbit-coupled Bose-Einstein condensates in a moving harmonic trap. Motivated by the concept of shortcuts to adiabaticity, we design inversely the time-dependent trap position and spin-orbit-coupling strength. By choosing appropriate boundary conditions we obtain fast transport and spin flip simultaneously. The nonadiabatic transport and relevant spin dynamics are illustrated with numerical examples and compared with the adiabatic transport with constant spin-orbit-coupling strength and velocity. Moreover, the influence of nonlinearity induced by interatomic interaction is discussed in terms of the Gross-Pitaevskii approach, showing the robustness of the proposed protocols. With the state-of-the-art experiments, such an inverse engineering technique paves the way for coherent control of spin-orbit-coupled Bose-Einstein condensates in harmonic traps.

Phase transition in the non-degenerate Hubbard Hamiltonian

International Nuclear Information System (INIS)

Chaves, C.M.; Lederer, P.; Gomes, A.A.

1976-01-01

Phase transition in the isotropic non-degenerate Hubbard Hamiltonian within the renormalization group techniques, using the epsilon = 4 - d expansion to first order in epsilon, is studied. The functional obtained from the Hubbard Hamiltonian displays full rotation symmetry and describes two coupled fields: a vector spin field, with n components and a non-soft scalar charge field. The possibility of tricritical behavior then emerges. The effects of simple constraints imposed on the charge field is considered. The relevance of the coupling between the fields in producing Fisher renormalization of the critical exponents is discussed. The possible singularities introduced in the charge-charge correlation function by the coupling are also discussed

Nonperturbative approach to the attractive Hubbard model

International Nuclear Information System (INIS)

Allen, S.; Tremblay, A.-M. S.

2001-01-01

A nonperturbative approach to the single-band attractive Hubbard model is presented in the general context of functional-derivative approaches to many-body theories. As in previous work on the repulsive model, the first step is based on a local-field-type ansatz, on enforcement of the Pauli principle and a number of crucial sumrules. The Mermin-Wagner theorem in two dimensions is automatically satisfied. At this level, two-particle self-consistency has been achieved. In the second step of the approximation, an improved expression for the self-energy is obtained by using the results of the first step in an exact expression for the self-energy, where the high- and low-frequency behaviors appear separately. The result is a cooperon-like formula. The required vertex corrections are included in this self-energy expression, as required by the absence of a Migdal theorem for this problem. Other approaches to the attractive Hubbard model are critically compared. Physical consequences of the present approach and agreement with Monte Carlo simulations are demonstrated in the accompanying paper (following this one)

On an uncorrelated jet model with Bose-Einstein statistics

International Nuclear Information System (INIS)

Bilic, N.; Dadic, I.; Martinis, M.

1978-01-01

Starting from the density of states of an ideal Bose-Einstein gas, an uncorrelated jet model with Bose-Einstein statistics has been formulated. The transition to continuum is based on the Touschek invariant measure. It has been shown that in this model average multiplicity increases logarithmically with total energy, while the inclusive distribution shows ln s violation of scaling. (author)

Effective interactions in a quantum Bose-Bose mixture

Science.gov (United States)

Utesov, O. I.; Baglay, M. I.; Andreev, S. V.

2018-05-01

We generalize the Beliaev diagrammatic theory of an interacting spinless Bose-Einstein condensate to the case of a binary mixture. We derive a set of coupled Dyson equations and find analytically the Green's functions of the system. The elementary excitation spectrum consists of two branches, one of which takes the characteristic parabolic form ω ∝p2 in the limit of a spin-independent interaction. We observe renormalization of the magnon mass and the spin-wave velocity due to the Andreev-Bashkin entrainment effect. For a three-dimensional weakly interacting gas the spectrum can be obtained by applying the Bogoliubov transformation to a second-quantized Hamiltonian in which the microscopic two-body potentials in each channel are replaced by the corresponding off-shell scattering amplitudes. The superfluid drag density can be calculated by considering a mixture of phonons and magnons interacting via the effective potentials. We show that this problem is identical to the second-order perturbative treatment of a Bose polaron. In two dimensions the drag contributes to the magnon dispersion already in the first approximation. Our consideration provides a basis for systematic study of emergent phases in quantum degenerate Bose-Bose mixtures.

Spontaneous creation of nonzero-angular-momentum modes in tunnel-coupled two-dimensional degenerate Bose gases

International Nuclear Information System (INIS)

Montgomery, T. W. A.; Scott, R. G.; Lesanovsky, I.; Fromhold, T. M.

2010-01-01

We investigate the dynamics of two tunnel-coupled two-dimensional degenerate Bose gases. The reduced dimensionality of the clouds enables us to excite specific angular momentum modes by tuning the coupling strength, thereby creating striking patterns in the atom density profile. The extreme sensitivity of the system to the coupling and initial phase difference results in a rich variety of subsequent dynamics, including vortex production, complex oscillations in relative atom number, and chiral symmetry breaking due to counter-rotation of the two clouds.

TRILEX and G W +EDMFT approach to d -wave superconductivity in the Hubbard model

Science.gov (United States)

Vučičević, J.; Ayral, T.; Parcollet, O.

2017-09-01

We generalize the recently introduced TRILEX approach (TRiply irreducible local EXpansion) to superconducting phases. The method treats simultaneously Mott and spin-fluctuation physics using an Eliashberg theory supplemented by local vertex corrections determined by a self-consistent quantum impurity model. We show that, in the two-dimensional Hubbard model, at strong coupling, TRILEX yields a d -wave superconducting dome as a function of doping. Contrary to the standard cluster dynamical mean field theory (DMFT) approaches, TRILEX can capture d -wave pairing using only a single-site effective impurity model. We also systematically explore the dependence of the superconducting temperature on the bare dispersion at weak coupling, which shows a clear link between strong antiferromagnetic (AF) correlations and the onset of superconductivity. We identify a combination of hopping amplitudes particularly favorable to superconductivity at intermediate doping. Finally, we study within G W +EDMFT the low-temperature d -wave superconducting phase at strong coupling in a region of parameter space with reduced AF fluctuations.

Cold Attractive Spin Polarized Fermi Lattice Gases and the Doped Positive U Hubbard Model

International Nuclear Information System (INIS)

Moreo, Adriana; Scalapino, D. J.

2007-01-01

Experiments on polarized fermion gases performed by trapping ultracold atoms in optical lattices allow the study of an attractive Hubbard model for which the strength of the on-site interaction is tuned by means of a Feshbach resonance. Using a well-known particle-hole transformation we discuss how results obtained for this system can be reinterpreted in the context of a doped repulsive Hubbard model. In particular, we show that the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state corresponds to the striped state of the two-dimensional doped positive U Hubbard model. We then use the results of numerical studies of the striped state to relate the periodicity of the FFLO state to the spin polarization. We also comment on the relationship of the d x 2 -y 2 superconducting phase of the doped 2D repulsive Hubbard model to a d-wave spin density wave state for the attractive case

Equation of state of the one- and three-dimensional Bose-Bose gases

Science.gov (United States)

Chiquillo, Emerson

2018-06-01

We calculate the equation of state of Bose-Bose gases in one and three dimensions in the framework of an effective quantum field theory. The beyond-mean-field approximation at zero temperature and the one-loop finite-temperature results are obtained performing functional integration on a local effective action. The ultraviolet divergent zero-point quantum fluctuations are removed by means of dimensional regularization. We derive the nonlinear Schrödinger equation to describe one- and three-dimensional Bose-Bose mixtures and solve it analytically in the one-dimensional scenario. This equation supports self-trapped brightlike solitonic droplets and self-trapped darklike solitons. At low temperature, we also find that the pressure and the number of particles of symmetric quantum droplets have a nontrivial dependence on the chemical potential and the difference between the intra- and the interspecies coupling constants.

Ferromagnetism in the Hubbard-Hirsch model

International Nuclear Information System (INIS)

Ivanov, V.A.; Zhuravlev, M.E.

1991-01-01

In the Hubbard model U=∞ the energy lowering due to exchange interaction of electrons of opposite spin in states with opposite bonding character is taken into account. In the electron concentration range 0< n<1 nonmonotonous dependence m(n) analogous to Slater-Pauling curves has been obtained. The Curle temperature having nonmonotonous dependence on n, saturated magnetization, the temperature dependences of magnetization have been obtained. (orig.)

Fidelity study of superconductivity in extended Hubbard models

Science.gov (United States)

Plonka, N.; Jia, C. J.; Wang, Y.; Moritz, B.; Devereaux, T. P.

2015-07-01

The Hubbard model with local on-site repulsion is generally thought to possess a superconducting ground state for appropriate parameters, but the effects of more realistic long-range Coulomb interactions have not been studied extensively. We study the influence of these interactions on superconductivity by including nearest- and next-nearest-neighbor extended Hubbard interactions in addition to the usual on-site terms. Utilizing numerical exact diagonalization, we analyze the signatures of superconductivity in the ground states through the fidelity metric of quantum information theory. We find that nearest and next-nearest neighbor interactions have thresholds above which they destabilize superconductivity regardless of whether they are attractive or repulsive, seemingly due to competing charge fluctuations.

Study of the two-dimensional Hubbard model at half-filling through constructive methods; Etude du modele de Hubbard bidimensionnel a demi remplissage par des methodes constructives

Energy Technology Data Exchange (ETDEWEB)

Afchain, St

2005-02-15

The Hubbard model is the simplest model to describe the behaviour of fermions on a network, it takes into account only fermion scattering and only interactions with other fermions located on the same site. Half-filling means that the total number of fermions is equal to half the number of sites. In the first chapter we show how we can pass trough successive approximations from a very general Hamiltonian to the Hubbard Hamiltonian. The second chapter is dedicated to the passage from the Hamiltonian formalism to the Grassmanian functional formalism. The main idea is to show that the correlation functions of the Hamiltonian approach can be described through fermionic functional integrals which implies the possibility of speaking of the model in terms of field theory. The chapter 3 deals with the main constructive techniques that allow the strict and consistent construction of models inside the frame of field theory. We show by proving the violation of a condition concerning self-energy, that the two-dimensional Hubbard model at half-filling has not the behaviour of a Fermi liquid in the Landau's interpretation. (A.C.)

Spectral properties near the Mott transition in the two-dimensional Hubbard model

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Kohno, Masanori

2013-03-01

Single-particle excitations near the Mott transition in the two-dimensional (2D) Hubbard model are investigated by using cluster perturbation theory. The Mott transition is characterized by the loss of the spectral weight from the dispersing mode that leads continuously to the spin-wave excitation of the Mott insulator. The origins of the dominant modes of the 2D Hubbard model near the Mott transition can be traced back to those of the one-dimensional Hubbard model. Various anomalous spectral features observed in cuprate high-temperature superconductors, such as the pseudogap, Fermi arc, flat band, doping-induced states, hole pockets, and spinon-like and holon-like branches, as well as giant kink and waterfall in the dispersion relation, are explained in a unified manner as properties near the Mott transition in a 2D system.

Bose-Einstein condensate in an optical lattice with Raman-assisted two-dimensional spin-orbit coupling

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Pan, Jian-Song; Zhang, Wei; Yi, Wei; Guo, Guang-Can

2016-10-01

In a recent experiment (Z. Wu, L. Zhang, W. Sun, X.-T. Xu, B.-Z. Wang, S.-C. Ji, Y. Deng, S. Chen, X.-J. Liu, and J.-W. Pan, arXiv:1511.08170 [cond-mat.quant-gas]), a Raman-assisted two-dimensional spin-orbit coupling has been realized for a Bose-Einstein condensate in an optical lattice potential. In light of this exciting progress, we study in detail key properties of the system. As the Raman lasers inevitably couple atoms to high-lying bands, the behaviors of the system in both the single- and many-particle sectors are significantly affected. In particular, the high-band effects enhance the plane-wave phase and lead to the emergence of "roton" gaps at low Zeeman fields. Furthermore, we identify high-band-induced topological phase boundaries in both the single-particle and the quasiparticle spectra. We then derive an effective two-band model, which captures the high-band physics in the experimentally relevant regime. Our results not only offer valuable insights into the two-dimensional lattice spin-orbit coupling, but also provide a systematic formalism to model high-band effects in lattice systems with Raman-assisted spin-orbit couplings.

Attractive Hubbard model: Homogeneous Ginzburg–Landau expansion and disorder

International Nuclear Information System (INIS)

Kuchinskii, E. Z.; Kuleeva, N. A.; Sadovskii, M. V.

2016-01-01

We derive a Ginzburg–Landau (GL) expansion in the disordered attractive Hubbard model within the combined Nozieres–Schmitt-Rink and DMFT+Σ approximation. Restricting ourselves to the homogeneous expansion, we analyze the disorder dependence of GL expansion coefficients for a wide range of attractive potentials U, from the weak BCS coupling region to the strong-coupling limit, where superconductivity is described by Bose–Einstein condensation (BEC) of preformed Cooper pairs. We show that for the a semielliptic “bare” density of states of the conduction band, the disorder influence on the GL coefficients A and B before quadratic and quartic terms of the order parameter, as well as on the specific heat discontinuity at the superconducting transition, is of a universal nature at any strength of the attractive interaction and is related only to the general widening of the conduction band by disorder. In general, disorder growth increases the values of the coefficients A and B, leading either to a suppression of the specific heat discontinuity (in the weak-coupling limit), or to its significant growth (in the strong-coupling region). However, this behavior actually confirms the validity of the generalized Anderson theorem, because the disorder dependence of the superconducting transition temperature T c , is also controlled only by disorder widening of the conduction band (density of states).

The Langevin method and Hubbard-like models

International Nuclear Information System (INIS)

Gross, M.; Hamber, H.

1989-01-01

The authors reexamine the difficulties associated with application of the Langevin method to numerical simulation of models with non-positive definite statistical weights, including the Hubbard model. They show how to avoid the violent crossing of the zeroes of the weight and how to move those nodes away from the real axis. However, it still appears necessary to keep track of the sign (or phase) of the weight

Self-trapping mechanisms in the dynamics of three coupled Bose-Einstein condensates

International Nuclear Information System (INIS)

Franzosi, Roberto; Penna, Vittorio

2002-01-01

We formulate the dynamics of three coupled Bose-Einstein condensates within a semiclassical scenario based on the standard boson coherent states. We compare such a picture with that of K. Nemoto et al. [Phys. Rev. A 63, 013604 (2001)] and show how our approach entails a simple formulation of the dimeric regime therein studied. This allows us to recognize the parameters that govern the bifurcation mechanism causing self-trapping, and paves the way to the construction of analytic solutions

p -wave superconductivity in weakly repulsive 2D Hubbard model with Zeeman splitting and weak Rashba spin-orbit coupling

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Hugdal, Henning G.; Sudbø, Asle

2018-01-01

We study the superconducting order in a two-dimensional square lattice Hubbard model with weak repulsive interactions, subject to a Zeeman field and weak Rashba spin-orbit interactions. Diagonalizing the noninteracting Hamiltonian leads to two separate bands, and by deriving an effective low-energy interaction we find the mean field gap equations for the superconducting order parameter on the bands. Solving the gap equations just below the critical temperature, we find that superconductivity is caused by Kohn-Luttinger-type interaction, while the pairing symmetry of the bands is indirectly affected by the spin-orbit coupling. The dominating attractive momentum channel of the Kohn-Luttinger term depends on the filling fraction n of the system, and it is therefore possible to change the momentum dependence of the order parameter by tuning n . Moreover, n also determines which band has the highest critical temperature. Rotating the magnetic field changes the momentum dependence from states that for small momenta reduce to a chiral px±i py type state for out-of-plane fields, to a nodal p -wave-type state for purely in-plane fields.

Stripe order from the perspective of the Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Devereaux, Thomas Peter

2018-03-01

A microscopic understanding of the strongly correlated physics of the cuprates must account for the translational and rotational symmetry breaking that is present across all cuprate families, commonly in the form of stripes. Here we investigate emergence of stripes in the Hubbard model, a minimal model believed to be relevant to the cuprate superconductors, using determinant quantum Monte Carlo (DQMC) simulations at finite temperatures and density matrix renormalization group (DMRG) ground state calculations. By varying temperature, doping, and model parameters, we characterize the extent of stripes throughout the phase diagram of the Hubbard model. Our results show that including the often neglected next-nearest-neighbor hopping leads to the absence of spin incommensurability upon electron-doping and nearly half-filled stripes upon hole-doping. The similarities of these findings to experimental results on both electron and hole-doped cuprate families support a unified description across a large portion of the cuprate phase diagram.

Vortices in spin-orbit-coupled Bose-Einstein condensates

International Nuclear Information System (INIS)

Radic, J.; Sedrakyan, T. A.; Galitski, V.; Spielman, I. B.

2011-01-01

Realistic methods to create vortices in spin-orbit-coupled Bose-Einstein condensates are discussed. It is shown that, contrary to common intuition, rotation of the trap containing a spin-orbit condensate does not lead to an equilibrium state with static vortex structures but gives rise instead to nonequilibrium behavior described by an intrinsically time-dependent Hamiltonian. We propose here the following alternative methods to induce thermodynamically stable static vortex configurations: (i) to rotate both the lasers and the anisotropic trap and (ii) to impose a synthetic Abelian field on top of synthetic spin-orbit interactions. Effective Hamiltonians for spin-orbit condensates under such perturbations are derived for most currently known realistic laser schemes that induce synthetic spin-orbit couplings. The Gross-Pitaevskii equation is solved for several experimentally relevant regimes. The new interesting effects include spatial separation of left- and right-moving spin-orbit condensates, the appearance of unusual vortex arrangements, and parity effects in vortex nucleation where the topological excitations are predicted to appear in pairs. All these phenomena are shown to be highly nonuniversal and depend strongly on a specific laser scheme and system parameters.

Energy levels of a spin-orbit-coupled Bose-Einstein condensate in a double-well potential

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Wang, Wen-Yuan; Cao, Hui; Zhu, Shi-Liang; Liu, Jie; Fu, Li-Bin

2015-02-01

We investigate the energy levels of a spin-orbit-coupled Bose-Einstein condensate in a double-well potential under the mean-field approximation. We find that the energy levels of the system can be significantly influenced by the atomic interactions. Without atomic interaction, four energy levels change linearly with the tunneling amplitude, the Raman coupling, and the spin-orbit coupling. However, whenever atomic interaction is considered, three more energy levels will appear, which have a nonlinear dependence on those parameters above. These three energy levels are multi-degenerate and related to the macro-symmetry of the system.

Interaction effect in the Kondo energy of the periodic Anderson-Hubbard model

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Itai, K.; Fazekas, P.

1996-07-01

We extend the periodic Anderson model by switching on a Hubbard U for the conduction band. The nearly integral valent limit of the Anderson-Hubbard model is studied with the Gutzwiller variational method. The lattice Kondo energy shows U dependence both in the prefactor and the exponent. Switching on U reduces the Kondo scale, which can be understood to result from the blocking of hybridization. At half filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator. Our findings should be relevant for a number of correlated two-band models of recent interest.

Superconducting correlations in the one-band Hubbard model with intermediate on-site and weak attractive intersite interactions

International Nuclear Information System (INIS)

Jain, K.P.; Ramakumar, R.; Chancey, C.C.

1990-01-01

In this paper, we analyze a simple extended Hubbard model with an intermediate on-site interaction (both repulsive and attractive) and a weak intersite attractive interaction. Following Hubbard decoupling approximations and introducing Hubbard subband operators, we obtain a generalized gap function for singlet s-wave pairing that explicitly depends on the Hubbard subband energies. For the on-site repulsive-interaction case, we find that the superconductivity is not destroyed in the intermediate-interaction regime, contrary to the prediction of a Hartree-Fock mean-field treatment. The essential consequence of the on-site repulsion is the formation of the Hubbard subbands separated by the Mott-Hubbard gap, and it is within these subbands that pairing induced by the intersite interaction occurs. For the attractive on-site interaction case, the on-site pairing amplitude is found to be proportional to the bandwidth, and the gap function has contributions from both on-site and intersite pairing. The relevance of the model to high-temperature superconductivity is discussed

Bose-Einstein condensation and chiral phase transition in linear sigma model

International Nuclear Information System (INIS)

Shu Song; Li Jiarong

2005-01-01

With the linear sigma model, we have studied Bose-Einstein condensation and the chiral phase transition in the chiral limit for an interacting pion system. A μ-T phase diagram including these two phenomena is presented. It is found that the phase plane has been divided into three areas: the Bose-Einstein condensation area, the chiral symmetry broken phase area and the chiral symmetry restored phase area. Bose-Einstein condensation can occur either from the chiral symmetry broken phase or from the restored phase. We show that the onset of the chiral phase transition is restricted in the area where there is no Bose-Einstein condensation

Ultracold Fermi and Bose gases and Spinless Bose Charged Sound Particles

Directory of Open Access Journals (Sweden)

Minasyan V.

2011-10-01

Full Text Available We propose a novel approach for investigation of the motion of Bose or Fermi liquid (or gas which consists of decoupled electrons and ions in the uppermost hyperfine state. Hence, we use such a concept as the fluctuation motion of “charged fluid particles” or “charged fluid points” representing a charged longitudinal elastic wave. In turn, this elastic wave is quantized by spinless longitudinal Bose charged sound particles with the rest mass m and charge e 0 . The existence of spinless Bose charged sound particles allows us to present a new model for description of Bose or Fermi liquid via a non-ideal Bose gas of charged sound particles . In this respect, we introduce a new postulation for the superfluid component of Bose or Fermi liquid determined by means of charged sound particles in the condensate, which may explain the results of experiments connected with ultra-cold Fermi gases of spin-polarized hydrogen, 6 Li and 40 K, and such a Bose gas as 87 Rb in the uppermost hyperfine state, where the Bose- Einstein condensation of charged sound particles is realized by tuning the magnetic field.

Methodes d'amas quantiques a temperature finie appliquees au modele de Hubbard

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Plouffe, Dany

Depuis leur decouverte dans les annees 80, les supraconducteurs a haute temperature critique ont suscite beaucoup d'interet en physique du solide. Comprendre l'origine des phases observees dans ces materiaux, telle la supraconductivite, est l'un des grands defis de la physique theorique du solide des 25 dernieres annees. L'un des mecanismes pressentis pour expliquer ces phenomenes est la forte interaction electron-electron. Le modele de Hubbard est l'un des modeles les plus simples pour tenir compte de ces interactions. Malgre la simplicite apparente de ce modele, certaines de ses caracteristiques, dont son diagramme de phase, ne sont toujours pas bien etablies, et ce malgre plusieurs avancements theoriques dans les dernieres annees. Cette etude se consacre a faire une analyse de methodes numeriques permettant de calculer diverses proprietes du modele de Hubbard en fonction de la temperature. Nous decrivons des methodes (la VCA et la CPT) qui permettent de calculer approximativement la fonction de Green a temperature finie sur un systeme infini a partir de la fonction de Green calculee sur un amas de taille finie. Pour calculer ces fonctions de Green, nous allons utiliser des methodes permettant de reduire considerablement les efforts numeriques necessaires pour les calculs des moyennes thermodynamiques, en reduisant considerablement l'espace des etats a considerer dans ces moyennes. Bien que cette etude vise d'abord a developper des methodes d'amas pour resoudre le modele de Hubbard a temperature finie de facon generale ainsi qu'a etudier les proprietes de base de ce modele, nous allons l'appliquer a des conditions qui s'approchent de supraconducteurs a haute temperature critique. Les methodes presentees dans cette etude permettent de tracer un diagramme de phase pour l'antiferromagnetisme et la supraconductivite qui presentent plusieurs similarites avec celui des supraconducteurs a haute temperature. Mots-cles : modele de Hubbard, thermodynamique

Long-wavelength spin-effective actions for the infinite U Hubbard model

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Braghin, Fábio L.

2013-04-01

The derivation of spin-effective actions is envisaged for the Hubbard model with infinite Coulomb repulsion for a very low concentration of holes with a slave fermion representation for electronic operators. For that, spinless charge variables (vacancies or holes) are integrated out and the resulting effective action at finite temperature is expanded up to the fourth order in the hopping term as proposed in reference [F.L. Braghin, A. Ferraz, E.A. Kochetov, Phys. Rev. B 78, 115109 (2008)] and, in a square lattice, the fourth order term is shown to have the structure of an extended gauge invariant J-Q model for localized spins. Two cases for which the resulting model is non trivial are analysed and they correspond basically to (1) holes hopping between two sub-lattices and (2) a time-dependent solution for the spinon variables in the square lattice. Whereas the first of these cases yields, at the leading order, an effective antiferromagnetic Heisenberg coupling for localized spins and the second one may lead either to ferromagnetic or antiferromagnetic effective coupling. In the second case, the ordering should appear rather in finite size domains and, although charge variables were integrated out, a subtle imbalance between charge degrees of freedom and spins should be at work.

Bond-order wave phase of the extended Hubbard model: Electronic solitons, paramagnetism, and coupling to Peierls and Holstein phonons

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Kumar, Manoranjan; Soos, Zoltán G.

2010-10-01

The bond-order wave (BOW) phase of the extended Hubbard model (EHM) in one dimension (1D) is characterized at intermediate correlation U=4t by exact treatment of N -site systems. Linear coupling to lattice (Peierls) phonons and molecular (Holstein) vibrations are treated in the adiabatic approximation. The molar magnetic susceptibility χM(T) is obtained directly up to N=10 . The goal is to find the consequences of a doubly degenerate ground state (gs) and finite magnetic gap Em in a regular array. Degenerate gs with broken inversion symmetry are constructed for finite N for a range of V near the charge-density-wave boundary at V≈2.18t where Em≈0.5t is large. The electronic amplitude B(V) of the BOW in the regular array is shown to mimic a tight-binding band with small effective dimerization δeff . Electronic spin and charge solitons are elementary excitations of the BOW phase and also resemble topological solitons with small δeff . Strong infrared intensity of coupled molecular vibrations in dimerized 1D systems is shown to extend to the regular BOW phase while its temperature dependence is related to spin solitons. The Peierls instability to dimerization has novel aspects for degenerate gs and substantial Em that suppresses thermal excitations. Finite Em implies exponentially small χM(T) at low temperature followed by an almost linear increase with T . The EHM with U=4t is representative of intermediate correlations in quasi-1D systems such as conjugated polymers or organic ion-radical and charge-transfer salts. The vibronic and thermal properties of correlated models with BOW phases are needed to identify possible physical realizations.

Elastic scattering of a Bose-Einstein condensate at a potential landscape

International Nuclear Information System (INIS)

Březinová, Iva; Burgdörfer, Joachim; Lode, Axel U J; Streltsov, Alexej I; Cederbaum, Lorenz S; Alon, Ofir E; Collins, Lee A; Schneider, Barry I

2014-01-01

We investigate the elastic scattering of Bose-Einstein condensates at shallow periodic and disorder potentials. We show that the collective scattering of the macroscopic quantum object couples to internal degrees of freedom of the Bose-Einstein condensate such that the Bose-Einstein condensate gets depleted. As a precursor for the excitation of the Bose-Einstein condensate we observe wave chaos within a mean-field theory

Effects of impurity and Bose-Fermi interactions on the transition temperature of a dilute dipolar Bose-Einstein condensation in trapped Bose-Fermi mixtures

Science.gov (United States)

Yavari, H.; Mokhtari, M.

2014-03-01

The effects of impurity and Bose-Fermi interactions on the transition temperature of a dipolar Bose-Einstein condensation in trapped Bose-Fermi mixture, by using the two-fluid model, are investigated. The shift of the transition temperature consists of four contributions due to contact, Bose-Fermi, dipole-dipole, and impurity interactions. We will show that in the presence of an anisotropic trap, the Bose-Fermi correction to the shift of transition temperature due to the excitation spectra of the thermal part is independent of anisotropy factor. Applying our results to trapped Bose-Fermi mixtures shows that, by knowing the impurity effect, the shift of the transition temperature due to Bose-Fermi interaction could be measured for isotropic trap (dipole-dipole contributions is zero) and Feshbach resonance technique (contact potential contribution is negligible).

Three-mode resonant coupling of collective excitations in a Bose-Einstein condensate

International Nuclear Information System (INIS)

Ma Yongli; Huang, Guoxiang; Hu Bambi

2005-01-01

We make a systematic study of the resonant mode coupling of the collective excitations at zero temperature in a Bose-Einstein condensate (BEC). (i) Based on the Gross-Pitaevskii equation we derive a set of nonlinearly coupled envelope equations for a three-mode resonant interaction (TMRI) by means of a method of multiple scales. (ii) We calculate the coupling matrix elements for the TMRI and show that the divergence appearing in previous studies can be eliminated completely by using a Fetter-like variational approximation for the ground-state wave function of the condensate. (iii) We provide the selection rules in mode-mode interaction processes [including TMRI and second-harmonic generation (SHG)] according to the symmetry of the excitations. (iv) By solving the nonlinearly coupled envelope equations we obtain divergence-free nonlinear amplitudes for the TMRI and SHG processes and show that our theoretical results on the shape oscillations of the condensate agree well with the experimental ones. We suggest also an experiment to check the theoretical prediction of the present study on the TMRI of collective excitations in a BEC

Many-body Anderson localization of strongly interacting bosons in random lattices

International Nuclear Information System (INIS)

Katzer, Roman

2015-05-01

In the present work, we investigate the problem of many-body localization of strongly interacting bosons in random lattices within the disordered Bose-Hubbard model. This involves treating both the local Mott-Hubbard physics as well as the non-local quantum interference processes, which give rise to the phenomenon of Anderson localization, within the same theory. In order to determine the interaction induced transition to the Mott insulator phase, it is necessary to treat the local particle interaction exactly. Therefore, here we use a mean-field approach that approximates only the kinetic term of the Hamiltonian. This way, the full problem of interacting bosons on a random lattice is reduced to a local problem of a single site coupled to a particle bath, which has to be solved self-consistently. In accordance to previous works, we find that a finite disorder width leads to a reduced size of the Mott insulating regions. The transition from the superfluid phase to the Bose glass phase is driven by the non-local effect of Anderson localization. In order to describe this transition, one needs to work within a theory that is non-local as well. Therefore, here we introduce a new approach to the problem. Based on the results for the local excitation spectrum obtained within the mean-field theory, we reduce the full, interacting model to an effective, non-interacting model by applying a truncation scheme to the Hilbert space. Evaluating the long-ranged current density within this approximation, we identify the transition from the Bose glass to the superfluid phase with the Anderson transition of the effective model. Resolving this transition using the self-consistent theory of localization, we obtain the full phase diagram of the disordered Bose-Hubbard model in the regime of strong interaction and larger disorder. In accordance to the theorem of inclusions, we find that the Mott insulator and the superfluid phase are always separated by the compressible, but insulating

Study of the two-dimensional Hubbard model at half-filling through constructive methods

International Nuclear Information System (INIS)

Afchain, St.

2005-02-01

The Hubbard model is the simplest model to describe the behaviour of fermions on a network, it takes into account only fermion scattering and only interactions with other fermions located on the same site. Half-filling means that the total number of fermions is equal to half the number of sites. In the first chapter we show how we can pass trough successive approximations from a very general Hamiltonian to the Hubbard Hamiltonian. The second chapter is dedicated to the passage from the Hamiltonian formalism to the Grassmanian functional formalism. The main idea is to show that the correlation functions of the Hamiltonian approach can be described through fermionic functional integrals which implies the possibility of speaking of the model in terms of field theory. The chapter 3 deals with the main constructive techniques that allow the strict and consistent construction of models inside the frame of field theory. We show by proving the violation of a condition concerning self-energy, that the two-dimensional Hubbard model at half-filling has not the behaviour of a Fermi liquid in the Landau's interpretation. (A.C.)

Vortices in trapped Bose-Einstein condensates

International Nuclear Information System (INIS)

Jackson, B.

2000-09-01

In this thesis we solve the Gross-Pitaevskii equation numerically in order to model the response of trapped Bose-Einstein condensed gases to perturbations by electromagnetic fields. First, we simulate output coupling of pulses from the condensate and compare our results to experiments. The excitation and separation of eigenmodes on flow through a constriction is also studied. We then move on to the main theme of this thesis: the important subject of quantised vortices in Bose condensates, and the relation between Bose-Einstein condensation and superfluidity. We propose methods of producing vortex pairs and rings by controlled motion of objects. Full three-dimensional simulations under realistic experimental conditions are performed in order to test the validity of these ideas. We link vortex formation to drag forces on the object, which in turn is connected with energy transfer to the condensate. We therefore argue that vortex formation by moving objects is intimately related to the onset of dissipation in superfluids. We discuss this idea in the context of a recent experiment, using simulations to provide evidence of vortex formation in the experimental scenario. Superfluidity is also manifest in the property of persistent currents, which is linked to vortex stability and dynamics. We simulate vortex line and ring motion, and find in both cases precessional motion and thermodynamic instability to dissipation. Strictly speaking, the Gross-Pitaevskii equation is valid only for temperatures far below the BEC transition. We end the thesis by describing a simple finite-temperature model to describe mean-field coupling between condensed and non-condensed components of the gas. We show that our hybrid Monte-Carlo/FFT technique can describe damping of the lowest energy excitations of the system. Extensions to this model and future research directions are discussed in the conclusion. (author)

Planar N = 4 gauge theory and the Hubbard model

International Nuclear Information System (INIS)

Rej, Adam; Serban, Didina; Staudacher, Matthias

2006-01-01

Recently it was established that a certain integrable long-range spin chain describes the dilatation operator of N = 4 gauge theory in the su(2) sector to at least three-loop order, while exhibiting BMN scaling to all orders in perturbation theory. Here we identify this spin chain as an approximation to an integrable short-ranged model of strongly correlated electrons: The Hubbard model

Dynamical Vertex Approximation for the Hubbard Model

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Toschi, Alessandro

A full understanding of correlated electron systems in the physically relevant situations of three and two dimensions represents a challenge for the contemporary condensed matter theory. However, in the last years considerable progress has been achieved by means of increasingly more powerful quantum many-body algorithms, applied to the basic model for correlated electrons, the Hubbard Hamiltonian. Here, I will review the physics emerging from studies performed with the dynamical vertex approximation, which includes diagrammatic corrections to the local description of the dynamical mean field theory (DMFT). In particular, I will first discuss the phase diagram in three dimensions with a special focus on the commensurate and incommensurate magnetic phases, their (quantum) critical properties, and the impact of fluctuations on electronic lifetimes and spectral functions. In two dimensions, the effects of non-local fluctuations beyond DMFT grow enormously, determining the appearance of a low-temperature insulating behavior for all values of the interaction in the unfrustrated model: Here the prototypical features of the Mott-Hubbard metal-insulator transition, as well as the existence of magnetically ordered phases, are completely overwhelmed by antiferromagnetic fluctuations of exponentially large extension, in accordance with the Mermin-Wagner theorem. Eventually, by a fluctuation diagnostics analysis of cluster DMFT self-energies, the same magnetic fluctuations are identified as responsible for the pseudogap regime in the holed-doped frustrated case, with important implications for the theoretical modeling of the cuprate physics.

Magnetic and superconducting competition within the Hubbard dimer. Exact solution

International Nuclear Information System (INIS)

Matlak, M.; Slomska, T.; Grabiec, B.

2005-01-01

We express the Hubbard dimer Hamiltonian H d =Σ 16 α=1 E α vertical stroke E α right angle left angle E α vertical stroke in the second quantization with the use of the Hubbard and spin operators. We consider the case of positive and negative U. We decompose the resulting Hamiltonian into several parts collecting all the terms belonging to the same energy level. Such a decomposition visualizes explicitly all intrinsic interactions competing together and deeply hidden in the original form of the dimer Hamiltonian. Among them are competitive ferromagnetic and antiferromagnetic interactions. There are also hopping terms present which describe Cooper pairs hopping between sites 1 and 2 with positive and negative coupling constants (similar as in Kulik-Pedan, Penson-Kolb models). We show that the competition between intrinsic interactions strongly depends on the model parameters and the averaged occupation number of electrons n element of [0, 4] resulting in different regimes of the model (as e.g. t-J model regime, etc.). (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates.

Science.gov (United States)

Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

2016-06-03

A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.

Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates

Science.gov (United States)

Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann

2016-06-01

A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.

Ground-state and spectral properties of an asymmetric Hubbard ladder

Science.gov (United States)

Abdelwahab, Anas; Jeckelmann, Eric; Hohenadler, Martin

2015-04-01

We investigate a ladder system with two inequivalent legs, namely, a Hubbard chain and a one-dimensional electron gas. Analytical approximations, the density-matrix renormalization group method, and continuous-time quantum Monte Carlo simulations are used to determine ground-state properties, gaps, and spectral functions of this system at half-filling. Evidence for the existence of four different phases as a function of the Hubbard interaction and the rung hopping is presented. First, a Luttinger liquid exists at very weak interchain hopping. Second, a Kondo-Mott insulator with spin and charge gaps induced by an effective rung exchange coupling is found at moderate interchain hopping or strong Hubbard interaction. Third, a spin-gapped paramagnetic Mott insulator with incommensurate excitations and pairing of doped charges is observed at intermediate values of the rung hopping and the interaction. Fourth, the usual correlated band insulator is recovered for large rung hopping. We show that the wave numbers of the lowest single-particle excitations are different in each insulating phase. In particular, the three gapped phases exhibit markedly different spectral functions. We discuss the relevance of asymmetric two-leg ladder systems as models for atomic wires deposited on a substrate.

Response of the Higgs amplitude mode of superfluid Bose gases in a three-dimensional optical lattice

Science.gov (United States)

Nagao, Kazuma; Takahashi, Yoshiro; Danshita, Ippei

2018-04-01

We study the Higgs mode of superfluid Bose gases in a three-dimensional optical lattice, which emerges near the quantum phase transition to the Mott insulator at commensurate fillings. Specifically, we consider responses of the Higgs mode to temporal modulations of the onsite interaction and the hopping energy. In order to calculate the response functions including the effects of quantum and thermal fluctuations, we map the Bose-Hubbard model onto an effective pseudospin-1 model and use a perturbative expansion based on the imaginary-time Green's function theory. We also include the effects of an inhomogeneous trapping potential by means of a local density approximation. We find that the response function for the hopping modulation is equal to that for the interaction modulation within our approximation. At the unit filling rate and in the absence of a trapping potential, we show that the Higgs mode can exist as a sharp resonance peak in the dynamical susceptibilities at typical temperatures. However, the resonance peak is significantly broadened due to the trapping potential when the modulations are applied globally to the entire system. We suggest that the Higgs mode can be detected as a sharp resonance peak by partial modulations around the trap center.

Thermalization of a quenched Bose-Josephson junction

Energy Technology Data Exchange (ETDEWEB)

Posazhennikova, Anna [Royal Holloway, University of London (United Kingdom); Trujillo-Martinez, Mauricio; Kroha, Johann [Universitaet Bonn (Germany)

2015-07-01

The experimental realization and control of quantum systems isolated from the environment, in ultracold atomic gases relaunched the interest in the fundamental non-equilibrium problem of how a finite system approaches thermal equilibrium. Despite intensive research there is still no conclusive answer to this question. We investigate theoretically how a quenched Bose-Josephson junction, where the Josephson coupling is switched on instantaneously, approaches its stationary state. We use the field theoretical approach for bosons out of equilibrium in a trap with discrete levels, developed by us previously. In this approach the operators for Bose-Einstein condensate (BEC) particles are treated on mean-field level, while excitations of the Bose gas in higher trap levels are treated fully quantum-mechanically. This leads to coupled equations of motion for the BEC amplitudes (Gross-Pitaevskii equation) and the quasiparticle propagators. The inelastic quasiparticle collisions responsible for the system relaxation during the time-dependent evolution are described within self-consistent second-order approximation.

One-particle versus two-particle crossover in weakly coupled Hubbard chains and ladders: perturbative renormalization group approach

International Nuclear Information System (INIS)

Kishine, Jun-Ichiro; Yonemitsu, Kenji

1998-01-01

Physical nature of dimensional crossovers in weakly coupled Hubbard chains and ladders has been discussed within the framework of the perturbative renormalization-group (PRG) approach. The difference between these two cases originates from different universality classes which the corresponding isolated systems belong to. In the present work, we discuss the nature of the dimensional crossovers in the weakly coupled chains and ladders, with emphasis on the difference between the two cases within the framework of the PRG approach. The difference of the universality class of the isolated chain and ladder profoundly affects the relevance or irrelevance of the inter-chain/ladder one-particle hopping. The strong coupling phase of the isolated ladder makes the one-particle process irrelevant so that the d-wave superconducting transition can be induced via the two-particle crossover in the weakly coupled ladders. The weak coupling phase of the isolated chain makes the one-particle process relevant so that the two-particle crossover can hardly be realized in the coupled chains. (Copyright (1998) World Scientific Publishing Co. Pte. Ltd)

Coherent tunneling of atoms from Bose-condensed gases at finite temperatures

International Nuclear Information System (INIS)

Luxat, David L.; Griffin, Allan

2002-01-01

Tunneling of atoms between two trapped Bose-condensed gases at finite temperatures is explored using a many-body linear-response tunneling formalism similar to that used in superconductors. To lowest order, the tunneling currents can be expressed quite generally in terms of the single-particle Green's functions of isolated Bose gases. A coherent first-order tunneling Josephson current between two atomic Bose-Einstein condensates is found, in addition to coherent and dissipative contributions from second-order condensate-noncondensate and noncondensate-noncondensate tunneling. Our work is a generalization of Meier and Zwerger, who recently treated tunneling between uniform atomic Bose gases. We apply our formalism to the analysis of an out-coupling experiment induced by light wave fields, using a simple Bogoliubov-Popov quasiparticle approximation for the trapped Bose gas. For tunneling into the vacuum, we recover the results of Japha, Choi, Burnett, and Band, who recently pointed out the usefulness of studying the spectrum of out-coupled atoms. In particular, we show that the small tunneling current of noncondensate atoms from a trapped Bose gas has a broad spectrum of energies, with a characteristic structure associated with the Bogoliubov quasiparticle u 2 and v 2 amplitudes

Comparison of a two electron with a two charged boson variational ...

African Journals Online (AJOL)

The results show only slight differences between the cases of the electrons and bosons. The implication that there is possibility of obtaining both condensates from the Hubbard model is then discussed in relation to superconductivity. Keywords: Bose Einstein condensation, superconductivity, Hubbard model, electrons, ...

Influence of spin and charge fluctuations on spectra of the two-dimensional Hubbard model

Science.gov (United States)

Sherman, A.

2018-05-01

The influence of spin and charge fluctuations on spectra of the two-dimensional fermionic Hubbard model is considered using the strong coupling diagram technique. Infinite sequences of diagrams containing ladder inserts, which describe the interaction of electrons with these fluctuations, are summed, and obtained equations are self-consistently solved for the ranges of Hubbard repulsions , temperatures and electron concentrations with t the intersite hopping constant. For all considered U the system exhibits a transition to the long-range antiferromagnetic order at . At the same time no indication of charge ordering is observed. Obtained solutions agree satisfactorily with results of other approaches and obey moments sum rules. In the considered region of the U-T plane, the curve separating metallic solutions passes from at the highest temperatures to U  =  2t at for half-filling. If only short-range fluctuations are allowed for the remaining part of this region is occupied by insulating solutions. Taking into account long-range fluctuations leads to strengthening of maxima tails, which transform a part of insulating solutions into bad-metal states. For low T, obtained results allow us to trace the gradual transition from the regime of strong correlations with the pronounced four-band structure and well-defined Mott gap for to the Slater regime of weak correlations with the spectral intensity having a dip along the boundary of the magnetic Brillouin zone due to an antiferromagnetic ordering for . For and doping leads to the occurrence of a pseudogap near the Fermi level, which is a consequence of the splitting out of a narrow band from a Hubbard subband. Obtained spectra feature waterfalls and Fermi arcs, which are similar to those observed in hole-doped cuprates.

Finite-temperature dynamics of the Mott insulating Hubbard chain

Science.gov (United States)

Nocera, Alberto; Essler, Fabian H. L.; Feiguin, Adrian E.

2018-01-01

We study the dynamical response of the half-filled one-dimensional Hubbard model for a range of interaction strengths U and temperatures T by a combination of numerical and analytical techniques. Using time-dependent density matrix renormalization group computations we find that the single-particle spectral function undergoes a crossover to a spin-incoherent Luttinger liquid regime at temperatures T ˜J =4 t2/U for sufficiently large U >4 t . At smaller values of U and elevated temperatures the spectral function is found to exhibit two thermally broadened bands of excitations, reminiscent of what is found in the Hubbard-I approximation. The dynamical density-density response function is shown to exhibit a finite-temperature resonance at low frequencies inside the Mott gap, with a physical origin similar to the Villain mode in gapped quantum spin chains. We complement our numerical computations by developing an analytic strong-coupling approach to the low-temperature dynamics in the spin-incoherent regime.

DMFT+Σ approach to disordered Hubbard model

International Nuclear Information System (INIS)

Kuchinskii, E. Z.; Sadovskii, M. V.

2016-01-01

We briefly review the generalized dynamic mean-field theory DMFT+Σ applied to both repulsive and attractive disordered Hubbard models. We examine the general problem of metal–insulator transition and the phase diagram in the repulsive case, as well as the BCS–BEC crossover region of the attractive model, demonstrating a certain universality of single-electron properties under disordering in both models. We also discuss and compare the results for the density of states and dynamic conductivity in the repulsive and attractive cases and the generalized Anderson theorem behavior of the superconducting critical temperature in the disordered attractive case. A brief discussion of the behavior of Ginzburg–Landau coefficients under disordering in the BCS–BEC crossover region is also presented.

Energetic and dynamical instability of spin-orbit coupled Bose-Einstein condensate in a deep optical lattice

Science.gov (United States)

Yu, Zi-Fa; Chai, Xu-Dan; Xue, Ju-Kui

2018-05-01

We investigate the energetic and dynamical instability of spin-orbit coupled Bose-Einstein condensate in a deep optical lattice via a tight-binding model. The stability phase diagram is completely revealed in full parameter space, while the dependence of superfluidity on the dispersion relation is illustrated explicitly. In the absence of spin-orbit coupling, the superfluidity only exists in the center of the Brillouin zone. However, the combination of spin-orbit coupling, Zeeman field, nonlinearity and optical lattice potential can modify the dispersion relation of the system, and change the position of Brillouin zone for generating the superfluidity. Thus, the superfluidity can appear in either the center or the other position of the Brillouin zone. Namely, in the center of the Brillouin zone, the system is either superfluid or Landau unstable, which depends on the momentum of the lowest energy. Therefore, the superfluidity can occur at optional position of the Brillouin zone by elaborating spin-orbit coupling, Zeeman splitting, nonlinearity and optical lattice potential. For the linear case, the system is always dynamically stable, however, the nonlinearity can induce the dynamical instability, and also expand the superfluid region. These predicted results can provide a theoretical evidence for exploring the superfluidity of the system experimentally.

Recent numerical results on the two dimensional Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Parola, A.; Sorella, S.; Baroni, S.; Car, R.; Parrinello, M.; Tosatti, E. (SISSA, Trieste (Italy))

1989-12-01

A new method for simulating strongly correlated fermionic systems, has been applied to the study of the ground state properties of the 2D Hubbard model at various fillings. Comparison has been made with exact diagonalizations in the 4 x 4 lattices where very good agreement has been verified in all the correlation functions which have been studied: charge, magnetization and momentum distribution. (orig.).

Recent numerical results on the two dimensional Hubbard model

International Nuclear Information System (INIS)

Parola, A.; Sorella, S.; Baroni, S.; Car, R.; Parrinello, M.; Tosatti, E.

1989-01-01

This paper reports a new method for simulating strongly correlated fermionic systems applied to the study of the ground state properties of the 2D Hubbard model at various fillings. Comparison has been made with exact diagonalizations in the 4 x 4 lattices where very good agreement has been verified in all the correlation functions which have been studied: charge, magnetization and momentum distribution

Effective field theories for correlated electrons

International Nuclear Information System (INIS)

Wallington, J.P.

1999-10-01

In this thesis, techniques of functional integration are applied to the construction of effective field theories for models of strongly correlated electrons. This is accomplished by means of the Hubbard-Stratonovic transformation which maps a system of interacting fermions onto one of free fermions interacting, not with each other, but with bosonic fields representing the collective modes of the system. Different choices of transformation are investigated throughout the thesis. It is shown that there exists a new group of discrete symmetries and transformations of the Hubbard model. Using this new group, the problem of choosing a Hubbard-Stratonovic decomposition of the Hubbard interaction term is solved. In the context of the exotic doped barium bismuthates, an extended Hubbard model with on-site attraction and nearest neighbour repulsion is studied. Mean field and renormalisation group analyses show a 'pseudospin-flop' from charge density wave to superconductivity as a function of filling. The nearest neighbour attractive Hubbard model on a quasi-2D lattice is studied as a simple phenomenological model for the high-T c cuprates. Mean field theory shows a transition from pure d-wave to pure s-wave superconductivity, via a mixed symmetry s + id state. Using Gaussian fluctuations, the BCS-Bose crossover is examined and suggestions are made about the origin of the angle dependence of the pseudogap. The continuum delta-shell potential model is introduced for anisotropic superconductors. Its mean field phases are studied and found to have some unusual properties. The BCS-Bose crossover is examined and the results are compared with those of the lattice model. Quasi-2D (highly anisotropic 3D) systems are considered. The critical properties of a Bose gas are investigated as the degree of anisotropy is varied. A new 2D Bose condensate state is found. A renormalisation group analysis is used to investigate the crossover from 2D to 3D. (author)

Strong-coupling Bose polarons out of equilibrium: Dynamical renormalization-group approach

Science.gov (United States)

Grusdt, Fabian; Seetharam, Kushal; Shchadilova, Yulia; Demler, Eugene

2018-03-01

When a mobile impurity interacts with a surrounding bath of bosons, it forms a polaron. Numerous methods have been developed to calculate how the energy and the effective mass of the polaron are renormalized by the medium for equilibrium situations. Here, we address the much less studied nonequilibrium regime and investigate how polarons form dynamically in time. To this end, we develop a time-dependent renormalization-group approach which allows calculations of all dynamical properties of the system and takes into account the effects of quantum fluctuations in the polaron cloud. We apply this method to calculate trajectories of polarons following a sudden quench of the impurity-boson interaction strength, revealing how the polaronic cloud around the impurity forms in time. Such trajectories provide additional information about the polaron's properties which are challenging to extract directly from the spectral function measured experimentally using ultracold atoms. At strong couplings, our calculations predict the appearance of trajectories where the impurity wavers back at intermediate times as a result of quantum fluctuations. Our method is applicable to a broader class of nonequilibrium problems. As a check, we also apply it to calculate the spectral function and find good agreement with experimental results. At very strong couplings, we predict that quantum fluctuations lead to the appearance of a dark continuum with strongly suppressed spectral weight at low energies. While our calculations start from an effective Fröhlich Hamiltonian describing impurities in a three-dimensional Bose-Einstein condensate, we also calculate the effects of additional terms in the Hamiltonian beyond the Fröhlich paradigm. We demonstrate that the main effect of these additional terms on the attractive side of a Feshbach resonance is to renormalize the coupling strength of the effective Fröhlich model.

Bose-Einstein correlation in Landau's model

International Nuclear Information System (INIS)

Hama, Y.; Padula, S.S.

1986-01-01

Bose-Einstein correlation is studied by taking an expanding fluid given by Landau's model as the source, where each space-time point is considered as an independent and chaotic emitting center with Planck's spectral distribution. As expected, the correlation depends on the relative angular positions as well as on the overall localization of the measuring system and it turns out that the average dimension of the source increases with the multiplicity N/sub ch/

Stationary states and rotational properties of spin-orbit-coupled Bose-Einstein condensates held under a toroidal trap

Science.gov (United States)

He, Zhang-Ming; Zhang, Xiao-Fei; Kato, Masaya; Han, Wei; Saito, Hiroki

2018-06-01

We consider a pseudospin-1/2 Bose-Einstein condensate with Rashba spin-orbit coupling in a two-dimensional toroidal trap. By solving the damped Gross-Pitaevskii equations for this system, we show that the system exhibits a rich variety of stationary states, such as vehicle wheel and flower-petal stripe patterns. These stationary states are stable against perturbation with thermal energy and can survive for a long time. In the presence of rotation, our results show that the rotating systems have exotic vortex configurations. These phenomenon originates from the interplay among spin-orbit coupling, trap geometry, and rotation.

Non-equilibrium coherence dynamics in one-dimensional Bose gases.

Science.gov (United States)

Hofferberth, S; Lesanovsky, I; Fischer, B; Schumm, T; Schmiedmayer, J

2007-09-20

Low-dimensional systems provide beautiful examples of many-body quantum physics. For one-dimensional (1D) systems, the Luttinger liquid approach provides insight into universal properties. Much is known of the equilibrium state, both in the weakly and strongly interacting regimes. However, it remains a challenge to probe the dynamics by which this equilibrium state is reached. Here we present a direct experimental study of the coherence dynamics in both isolated and coupled degenerate 1D Bose gases. Dynamic splitting is used to create two 1D systems in a phase coherent state. The time evolution of the coherence is revealed through local phase shifts of the subsequently observed interference patterns. Completely isolated 1D Bose gases are observed to exhibit universal sub-exponential coherence decay, in excellent agreement with recent predictions. For two coupled 1D Bose gases, the coherence factor is observed to approach a non-zero equilibrium value, as predicted by a Bogoliubov approach. This coupled-system decay to finite coherence is the matter wave equivalent of phase-locking two lasers by injection. The non-equilibrium dynamics of superfluids has an important role in a wide range of physical systems, such as superconductors, quantum Hall systems, superfluid helium and spin systems. Our experiments studying coherence dynamics show that 1D Bose gases are ideally suited for investigating this class of phenomena.

Many-body localization proximity effects in platforms of coupled spins and bosons

Science.gov (United States)

Marino, J.; Nandkishore, R. M.

2018-02-01

We discuss the onset of many-body localization in a one-dimensional system composed of a XXZ quantum spin chain and a Bose-Hubbard model linearly coupled together. We consider two complementary setups, depending whether spatial disorder is initially imprinted on spins or on bosons; in both cases, we explore the conditions for the disordered portion of the system to localize by proximity of the other clean half. Assuming that the dynamics of one of the two parts develops on shorter time scales than the other, we can adiabatically eliminate the fast degrees of freedom, and derive an effective Hamiltonian for the system's remainder using projection operator techniques. Performing a locator expansion on the strength of the many-body interaction term or on the hopping amplitude of the effective Hamiltonian thus derived, we present results on the stability of the many-body localized phases induced by proximity effect. We also briefly comment on the feasibility of the proposed model through modern quantum optics architectures, with the long-term perspective to realize experimentally, in composite open systems, Anderson or many-body localization proximity effects.

Searching for Supersolidity in Ultracold Atomic Bose Condensates with Rashba Spin-Orbit Coupling

Science.gov (United States)

Liao, Renyuan

2018-04-01

We developed a functional integral formulation for the stripe phase of spinor Bose-Einstein condensates with Rashba spin-orbit coupling. The excitation spectrum is found to exhibit double gapless band structures, identified to be two Goldstone modes resulting from spontaneously broken internal gauge symmetry and translational invariance symmetry. The sound velocities display anisotropic behavior with the lower branch vanishing in the direction perpendicular to the stripe in the x -y plane. At the transition point between the plane-wave phase and the stripe phase, physical quantities such as fluctuation correction to the ground-state energy and quantum depletion of the condensates exhibit discontinuity, characteristic of the first-order phase transition. Despite strong quantum fluctuations induced by Rashba spin-orbit coupling, we show that the supersolid phase is stable against quantum depletion. Finally, we extend our formulation to finite temperatures to account for interactions between excitations.

Modelling Bose-Einstein correlations at LEP-2

International Nuclear Information System (INIS)

Loennblad, L.

1998-01-01

Some pros and cons of different strategies for modelling Bose-Einstein correlations in event generators for fully hadronic WW events at LEP-2 are discussed. A few new algorithms based on shifting final-state momenta of identical bosons in WW events generated by PYTHIA are also presented and the resulting predictions for the effects on the W mass measurement are discussed. (author)

Superconducting properties of the η-pairing state in the Penson-Kolb-Hubbard model

International Nuclear Information System (INIS)

Czart, W.R.; Robaszkiewicz, S.

2004-01-01

The Penson-Kolb-Hubbard model, i.e. the Hubbard model with the pair-hopping interaction J is studied. We focus on the properties of the superconducting state with the Cooper-pair center-of mass momentum q Q(η-phase). The transition into the η-phase, which is favorized by the repulsive J (J c |, dependent on band filling, on-site interaction U and band structure, and the system never exhibits standard BCS-like features. This is in obvious contrast with the properties of the isotropic s-wave state, stabilized by the attractive J and attractive U, which exhibit at T = 0 a smooth crossover from the BCS-like limit to that of tightly bound pairs with increasing pairing strength. (author)

Resummation of Infrared Divergencies in the Theory of Atomic Bose Gases

NARCIS (Netherlands)

Stoof, H.T.C.; van Heugten, J. J. R. M.

2014-01-01

We present a general strong-coupling approach for the description of an atomic Bose gas beyond the Bogoliubov approximation, when infrared divergences start to occur that need to be resummed exactly. We consider the determination of several important physical properties of the Bose gas, namely the

Spinor bose gases in cubic optical lattice

International Nuclear Information System (INIS)

Mobarak, Mohamed Saidan Sayed Mohamed

2014-01-01

In recent years the quantum simulation of condensed-matter physics problems has resulted from exciting experimental progress in the realm of ultracold atoms and molecules in optical lattices. In this thesis 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 with a linear Zeeman effect, we work out a Ginzburg-Landau theory for the underlying spin-1 Bose-Hubbard model. To this end we add artificial symmetry-breaking currents to the spin-1 Bose-Hubbard Hamiltonian in order to break the global U (1) symmetry. With this we determine a diagrammatic expansion of the grand-canonical free energy up to fourth order in the symmetry-breaking currents and up to the leading non-trivial order in the hopping strength which is of first order. As a cross-check we demonstrate that the resulting grand-canonical free energy allows to recover the mean-field theory. Applying a Legendre transformation to the grand-canonical free energy, where the symmetry-breaking currents are transformed to order parameters, we obtain the effective Ginzburg-Landau action. With this we calculate in detail at zero temperature the Mott insulator-superfluid quantum phase boundary as well as condensate and particle number density in the superfluid phase. We find that both mean-field and Ginzburg-Landau theory yield the same quantum phase transition between the Mott insulator and superfluid phases, but the range of validity of the mean-field theory turns out to be smaller than that of the Ginzburg-Landau theory. Due to this finding we expect that the Ginzburg-Landau theory gives better results for the superfluid phase and, thus, we restrict ourselves to extremize only the effective Ginzburg-Landau action with respect to the order parameters. Without external magnetic field the superfluid phase is a polar (ferromagnetic) state for anti-ferromagnetic (ferromagnetic) interactions, i.e. only the

Stability of superfluid phases in the 2D spin-polarized attractive Hubbard model

Science.gov (United States)

Kujawa-Cichy, A.; Micnas, R.

2011-08-01

We study the evolution from the weak coupling (BCS-like limit) to the strong coupling limit of tightly bound local pairs (LPs) with increasing attraction, in the presence of the Zeeman magnetic field (h) for d=2, within the spin-polarized attractive Hubbard model. The broken symmetry Hartree approximation as well as the strong coupling expansion are used. We also apply the Kosterlitz-Thouless (KT) scenario to determine the phase coherence temperatures. For spin-independent hopping integrals (t↑=t↓), we find no stable homogeneous polarized superfluid (SCM) state in the ground state for the strong attraction and obtain that for a two-component Fermi system on a 2D lattice with population imbalance, phase separation (PS) is favoured for a fixed particle concentration, even on the LP (BEC) side. We also examine the influence of spin-dependent hopping integrals (mass imbalance) on the stability of the SCM phase. We find a topological quantum phase transition (Lifshitz type) from the unpolarized superfluid phase (SC0) to SCM and tricritical points in the h-|U| and t↑/t↓-|U| ground-state phase diagrams. We also construct the finite temperature phase diagrams for both t↑=t↓ and t↑≠t↓ and analyze the possibility of occurrence of a spin-polarized KT superfluid.

Possible coexistence of antiferromagnetism and superconductivity in the Hubbard model

International Nuclear Information System (INIS)

Su Zhaobin; Dong Jinming; Yu Lu; Shen Juelian

1988-01-01

The Hubbard model in the nearly half-filled case was studied in the mean field approximation using the effective Hamiltonian approach. Both antiferromagnetic order parameter and condensation of singlet pairs were considered. In certain parameter ranges the coexistence of antiferromagnetism and superconductivity is energetically favourable. Relevance to the high temperature superconductivity and other theoretical approaches is also discussed. (author). 10 refs, 3 figs

Collective excitations of strongly coupled bilayer charged Bose liquids in the third-frequency-moment sum rule

International Nuclear Information System (INIS)

Tas, Murat; Tanatar, B.

2008-01-01

We calculate the collective excitation modes of strongly coupled bilayer charged Bose systems. We employ the dielectric matrix formulation to study the correlation effects within the random-phase approximation (RPA), the self consistent field approximation Singwi, Tosi, Land, and Sjoelander (STLS), and the quasilocalized charge approximation (QLCA), which satisfies the third-frequency-moment ( 3 >) sum rule. We find that the QLCA predicts a long-wavelength correlation-induced energy gap in the out-of-phase plasmon mode, similar to the situation in electronic bilayer systems. The energy gap and the plasmon density of states are studied as a function of interlayer separation and coupling parameter r s . The results should be helpful for experimental investigations

Recent developments in Bose-Einstein condensation

International Nuclear Information System (INIS)

Kalman, G.

1997-01-01

This paper contains viewgraphs on developments on Bose-Einstein condensation. Some topics covered are: strongly coupled coulomb systems; standard response functions of the first and second kind; dynamical mean field theory; quasi localized charge approximation; and the main equations

Recent developments in Bose-Einstein condensation

Energy Technology Data Exchange (ETDEWEB)

Kalman, G.

1997-09-22

This paper contains viewgraphs on developments on Bose-Einstein condensation. Some topics covered are: strongly coupled coulomb systems; standard response functions of the first and second kind; dynamical mean field theory; quasi localized charge approximation; and the main equations.

Periodic Ground State Configurations in a One-Dimensional Hubbard Model of Statistical Mechanics

International Nuclear Information System (INIS)

Kipnis, M. M.

2000-01-01

This paper considers an averaging procedure for the description of a particles arrangement in a Hubbard model with antiferromagnetic interactions. The arrangements are described by the devil's staircase. Completeness of the staircase is proved

Low-lying Photoexcited States of a One-Dimensional Ionic Extended Hubbard Model

Science.gov (United States)

Yokoi, Kota; Maeshima, Nobuya; Hino, Ken-ichi

2017-10-01

We investigate the properties of low-lying photoexcited states of a one-dimensional (1D) ionic extended Hubbard model at half-filling. Numerical analysis by using the full and Lanczos diagonalization methods shows that, in the ionic phase, there exist low-lying photoexcited states below the charge transfer gap. As a result of comparison with numerical data for the 1D antiferromagnetic (AF) Heisenberg model, it was found that, for a small alternating potential Δ, these low-lying photoexcited states are spin excitations, which is consistent with a previous analytical study [Katsura et al., link ext-link-type="uri" xlink:href="https://doi.org/10.1103/PhysRevLett.103.177402" xlink:type="simple">Phys. Rev. Lett. 103, 177402 (2009)link>]. As Δ increases, the spectral intensity of the 1D ionic extended Hubbard model rapidly deviates from that of the 1D AF Heisenberg model and it is clarified that this deviation is due to the neutral-ionic domain wall, an elementary excitation near the neutral-ionic transition point.

Dynamics of bright-bright solitons in Bose-Einstein condensate with Raman-induced one-dimensional spin-orbit coupling

Science.gov (United States)

Wen, Lin; Zhang, Xiao-Fei; Hu, Ai-Yuan; Zhou, Jing; Yu, Peng; Xia, Lei; Sun, Qing; Ji, An-Chun

2018-03-01

We investigate the dynamics of bright-bright solitons in one-dimensional two-component Bose-Einstein condensates with Raman-induced spin-orbit coupling, via the variational approximation and the numerical simulation of Gross-Pitaevskii equations. For the uniform system without trapping potential, we obtain two population balanced stationary solitons. By performing the linear stability analysis, we find a Goldstone eigenmode and an oscillation eigenmode around these stationary solitons. Moreover, we derive a general dynamical solution to describe the center-of-mass motion and spin evolution of the solitons under the action of spin-orbit coupling. The effects of a harmonic trap have also been discussed.

Trap-size scaling in confined-particle systems at quantum transitions

International Nuclear Information System (INIS)

Campostrini, Massimo; Vicari, Ettore

2010-01-01

We develop a trap-size scaling theory for trapped particle systems at quantum transitions. As a theoretical laboratory, we consider a quantum XY chain in an external transverse field acting as a trap for the spinless fermions of its quadratic Hamiltonian representation. We discuss trap-size scaling at the Mott insulator to superfluid transition in the Bose-Hubbard model. We present exact and accurate numerical results for the XY chain and for the low-density Mott transition in the hard-core limit of the one-dimensional Bose-Hubbard model. Our results are relevant for systems of cold atomic gases in optical lattices.

Correlation mediated superconductivity in a Spin Peierls Phase of the Hubbard Model

International Nuclear Information System (INIS)

Long, M.W.

1987-08-01

The author explores the consequences of a mapping of the Hubbard Hamiltonian with a view to finding possible superconducting phases. The transformation pairs up all the sites and is therefore a much more natural starting point for describing a 'Spin Peierls' transition, generating enhanced singlet correlations for this pairing, than it is for describing the 'Resonating Valence Bond' state. It is shown that in the less than half filling case, an effective non-linear hopping Hamiltonian is quite useful in describing half of the electrons. This effective Hamiltonian can show a form of superconducting instability when nearest neighbour hopping is introduced to stabilise it. This superconducting phase seems to be a very unlikely possibility for the standard Hubbard model. (author)

``Models'' CAVEAT EMPTOR!!!: ``Toy Models Too-Often Yield Toy-Results''!!!: Statistics, Polls, Politics, Economics, Elections!!!: GRAPH/Network-Physics: ``Equal-Distribution for All'' TRUMP-ED BEC ``Winner-Take-All'' ``Doctor Livingston I Presume?''

Science.gov (United States)

Preibus-Norquist, R. N. C.-Grover; Bush-Romney, G. W.-Willard-Mitt; Dimon, J. P.; Adelson-Koch, Sheldon-Charles-David-Sheldon; Krugman-Axelrod, Paul-David; Siegel, Edward Carl-Ludwig; D. N. C./O. F. P./''47''%/50% Collaboration; R. N. C./G. O. P./''53''%/49% Collaboration; Nyt/Wp/Cnn/Msnbc/Pbs/Npr/Ft Collaboration; Ftn/Fnc/Fox/Wsj/Fbn Collaboration; Lb/Jpmc/Bs/Boa/Ml/Wamu/S&P/Fitch/Moodys/Nmis Collaboration

2013-03-01

``Models''? CAVEAT EMPTOR!!!: ``Toy Models Too-Often Yield Toy-Results''!!!: Goldenfeld[``The Role of Models in Physics'', in Lects.on Phase-Transitions & R.-G.(92)-p.32-33!!!]: statistics(Silver{[NYTimes; Bensinger, ``Math-Geerks Clearly-Defeated Pundits'', LATimes, (11/9/12)])}, polls, politics, economics, elections!!!: GRAPH/network/net/...-PHYSICS Barabasi-Albert[RMP (02)] (r,t)-space VERSUS(???) [Where's the Inverse/ Dual/Integral-Transform???] (Benjamin)Franklin(1795)-Fourier(1795; 1897;1822)-Laplace(1850)-Mellin (1902) Brillouin(1922)-...(k,)-space, {Hubbard [The World According to Wavelets,Peters (96)-p.14!!!/p.246: refs.-F2!!!]},and then (2) Albert-Barabasi[]Bose-Einstein quantum-statistics(BEQS) Bose-Einstein CONDENSATION (BEC) versus Bianconi[pvt.-comm.; arXiv:cond-mat/0204506; ...] -Barabasi [???] Fermi-Dirac

Fidelity study of the superconducting phase diagram in the two-dimensional single-band Hubbard model

Science.gov (United States)

Jia, C. J.; Moritz, B.; Chen, C.-C.; Shastry, B. Sriram; Devereaux, T. P.

2011-09-01

Extensive numerical studies have demonstrated that the two-dimensional single-band Hubbard model contains much of the key physics in cuprate high-temperature superconductors. However, there is no definitive proof that the Hubbard model truly possesses a superconducting ground state or, if it does, of how it depends on model parameters. To answer these longstanding questions, we study an extension of the Hubbard model including an infinite-range d-wave pair field term, which precipitates a superconducting state in the d-wave channel. Using exact diagonalization on 16-site square clusters, we study the evolution of the ground state as a function of the strength of the pairing term. This is achieved by monitoring the fidelity metric of the ground state, as well as determining the ratio between the two largest eigenvalues of the d-wave pair/spin/charge-density matrices. The calculations show a d-wave superconducting ground state in doped clusters bracketed by a strong antiferromagnetic state at half filling controlled by the Coulomb repulsion U and a weak short-range checkerboard charge ordered state at larger hole doping controlled by the next-nearest-neighbor hopping t'. We also demonstrate that negative t' plays an important role in facilitating d-wave superconductivity.

Fermi states of Bose systems in three space dimensions

International Nuclear Information System (INIS)

Garbaczewski, P.

1985-01-01

Recently an exact spectral solution was constructed by Sudarshan and Tata for the (NTHETA) Fermi version of the Lee model. We demonstrate that it provides a partial solution for the related pure Bose spectral problems. Moreover, the (NTHETA) Bose (Bolsterli--Nelson) version of the Lee model is shown to possess Fermi partners, both exhibiting the partial solubility interplay: finding solutions in the Fermi case would presumably be easier than in the original Bose model. Fermi states of the underlying Bose systems in three space dimensions are explicitly identified

Madelung and Hubbard interactions in polaron band model of doped organic semiconductors

Science.gov (United States)

Png, Rui-Qi; Ang, Mervin C.Y.; Teo, Meng-How; Choo, Kim-Kian; Tang, Cindy Guanyu; Belaineh, Dagmawi; Chua, Lay-Lay; Ho, Peter K.H.

2016-01-01

The standard polaron band model of doped organic semiconductors predicts that density-of-states shift into the π–π* gap to give a partially filled polaron band that pins the Fermi level. This picture neglects both Madelung and Hubbard interactions. Here we show using ultrahigh workfunction hole-doped model triarylamine–fluorene copolymers that Hubbard interaction strongly splits the singly-occupied molecular orbital from its empty counterpart, while Madelung (Coulomb) interactions with counter-anions and other carriers markedly shift energies of the frontier orbitals. These interactions lower the singly-occupied molecular orbital band below the valence band edge and give rise to an empty low-lying counterpart band. The Fermi level, and hence workfunction, is determined by conjunction of the bottom edge of this empty band and the top edge of the valence band. Calculations are consistent with the observed Fermi-level downshift with counter-anion size and the observed dependence of workfunction on doping level in the strongly doped regime. PMID:27582355

Rabi dynamics of coupled atomic and molecular Bose-Einstein condensates

International Nuclear Information System (INIS)

Ishkhanyan, Artur; Chernikov, G.P.; Nakamura, Hiroki

2004-01-01

The dynamics of coherent Rabi oscillations in coupled atomic and molecular Bose-Einstein condensates is considered taking into account the atom-atom, atom-molecule, and molecule-molecule elastic interactions. The exact solution for the molecule formation probability is derived in terms of the elliptic functions. The two-dimensional space of the involved parameters intensity and detuning is analyzed and divided into two regions where the Rabi oscillations show different characteristics. A resonance curve is found, on which the molecular formation probability monotonically increases as a function of time. The maximum value of the final transition probability on this curve is 1/2 (i.e., total transition to the molecular state) and it is achieved at high field intensities starting from a minimal threshold defined by the interspecies interaction scattering lights. The explicit form of the resonance curve is determined, and it is shown that the resonance frequency position reveals a nonlinear dependence on the Rabi frequency of the applied field. A singular point is found on the resonance curve, where a power-law time evolution of the system is observed

Analysis of the dynamical cluster approximation for the Hubbard model

OpenAIRE

Aryanpour, K.; Hettler, M. H.; Jarrell, M.

2002-01-01

We examine a central approximation of the recently introduced Dynamical Cluster Approximation (DCA) by example of the Hubbard model. By both analytical and numerical means we study non-compact and compact contributions to the thermodynamic potential. We show that approximating non-compact diagrams by their cluster analogs results in a larger systematic error as compared to the compact diagrams. Consequently, only the compact contributions should be taken from the cluster, whereas non-compact ...

The classical trigonometric r-matrix for the quantum-deformed Hubbard chain

Energy Technology Data Exchange (ETDEWEB)

Beisert, Niklas, E-mail: nbeisert@aei.mpg.de [Max-Planck-Institut fuer Gravitationsphysik, Albert-Einstein-Institut, Am Muehlenberg 1, 14476 Potsdam (Germany)

2011-07-01

The one-dimensional Hubbard model is an exceptional integrable spin chain which is apparently based on a deformation of the Yangian for the superalgebra gl(2|2). Here we investigate the quantum deformation of the Hubbard model in the classical limit. This leads to a novel classical r-matrix of trigonometric kind. We derive the corresponding one-parameter family of Lie bialgebras as a deformation of the affine gl(2|2) Kac-Moody superalgebra. In particular, we discuss the affine extension as well as discrete symmetries, and we scan for simpler limiting cases, such as the rational r-matrix for the undeformed Hubbard model.

Vortex sorter for Bose-Einstein condensates

International Nuclear Information System (INIS)

Whyte, Graeme; Veitch, John; Courtial, Johannes; Oehberg, Patrik

2004-01-01

We have designed interferometers that sort Bose-Einstein condensates into their vortex components. The Bose-Einstein condensates in the two arms of the interferometer are rotated with respect to each other through fixed angles; different vortex components then exit the interferometer in different directions. The method we use to rotate the Bose-Einstein condensates involves asymmetric phase imprinting and is itself new. We have modeled rotation through fixed angles and sorting into vortex components with even and odd values of the topological charge of two-dimensional Bose-Einstein condensates in a number of states (pure or superposition vortex states for different values of the scattering length). Our scheme may have applications for quantum information processing

On the SU(2)× SU(2) symmetry in the Hubbard model

Science.gov (United States)

Jakubczyk, Dorota; Jakubczyk, Paweł

2012-08-01

We discuss the one-dimensional Hubbard model, on finite sites spin chain, in context of the action of the direct product of two unitary groups SU(2)× SU(2). The symmetry revealed by this group is applicable in the procedure of exact diagonalization of the Hubbard Hamiltonian. This result combined with the translational symmetry, given as the basis of wavelets of the appropriate Fourier transforms, provides, besides the energy, additional conserved quantities, which are presented in the case of a half-filled, four sites spin chain. Since we are dealing with four elementary excitations, two quasiparticles called "spinons", which carry spin, and two other called "holon" and "antyholon", which carry charge, the usual spin- SU(2) algebra for spinons and the so called pseudospin-SU(2) algebra for holons and antiholons, provide four additional quantum numbers.

Mass-imbalanced ionic Hubbard chain

Science.gov (United States)

Sekania, Michael; Baeriswyl, Dionys; Jibuti, Luka; Japaridze, George I.

2017-07-01

A repulsive Hubbard model with both spin-asymmetric hopping (t↑≠t↓ ) and a staggered potential (of strength Δ ) is studied in one dimension. The model is a compound of the mass-imbalanced (t↑≠t↓ ,Δ =0 ) and ionic (t↑=t↓ ,Δ >0 ) Hubbard models, and may be realized by cold atoms in engineered optical lattices. We use mostly mean-field theory to determine the phases and phase transitions in the ground state for a half-filled band (one particle per site). We find that a period-two modulation of the particle (or charge) density and an alternating spin density coexist for arbitrary Hubbard interaction strength, U ≥0 . The amplitude of the charge modulation is largest at U =0 , decreases with increasing U and tends to zero for U →∞ . The amplitude for spin alternation increases with U and tends to saturation for U →∞ . Charge order dominates below a value Uc, whereas magnetic order dominates above. The mean-field Hamiltonian has two gap parameters, Δ↑ and Δ↓, which have to be determined self-consistently. For U Uc they have different signs, and for U =Uc one gap parameter jumps from a positive to a negative value. The weakly first-order phase transition at Uc can be interpreted in terms of an avoided criticality (or metallicity). The system is reluctant to restore a symmetry that has been broken explicitly.

Conductivite dans le modele de Hubbard bi-dimensionnel a faible couplage

Science.gov (United States)

Bergeron, Dominic

Le modele de Hubbard bi-dimensionnel (2D) est souvent considere comme le modele minimal pour les supraconducteurs a haute temperature critique a base d'oxyde de cuivre (SCHT). Sur un reseau carre, ce modele possede les phases qui sont communes a tous les SCHT, la phase antiferromagnetique, la phase supraconductrice et la phase dite du pseudogap. Il n'a pas de solution exacte, toutefois, plusieurs methodes approximatives permettent d'etudier ses proprietes de facon numerique. Les proprietes optiques et de transport sont bien connues dans les SCHT et sont donc de bonne candidates pour valider un modele theorique et aider a comprendre mieux la physique de ces materiaux. La presente these porte sur le calcul de ces proprietes pour le modele de Hubbard 2D a couplage faible ou intermediaire. La methode de calcul utilisee est l'approche auto-coherente a deux particules (ACDP), qui est non-perturbative et inclue l'effet des fluctuations de spin et de charge a toutes les longueurs d'onde. La derivation complete de l'expression de la conductivite dans l'approche ACDP est presentee. Cette expression contient ce qu'on appelle les corrections de vertex, qui tiennent compte des correlations entre quasi-particules. Pour rendre possible le calcul numerique de ces corrections, des algorithmes utilisant, entre autres, des transformees de Fourier rapides et des splines cubiques sont developpes. Les calculs sont faits pour le reseau carre avec sauts aux plus proches voisins autour du point critique antiferromagnetique. Aux dopages plus faibles que le point critique, la conductivite optique presente une bosse dans l'infrarouge moyen a basse temperature, tel qu'observe dans plusieurs SCHT. Dans la resistivite en fonction de la temperature, on trouve un comportement isolant dans le pseudogap lorsque les corrections de vertex sont negligees et metallique lorsqu'elles sont prises en compte. Pres du point critique, la resistivite est lineaire en T a basse temperature et devient

Coulomb matrix elements in multi-orbital Hubbard models.

Science.gov (United States)

Bünemann, Jörg; Gebhard, Florian

2017-04-26

Coulomb matrix elements are needed in all studies in solid-state theory that are based on Hubbard-type multi-orbital models. Due to symmetries, the matrix elements are not independent. We determine a set of independent Coulomb parameters for a d-shell and an f-shell and all point groups with up to 16 elements (O h , O, T d , T h , D 6h , and D 4h ). Furthermore, we express all other matrix elements as a function of the independent Coulomb parameters. Apart from the solution of the general point-group problem we investigate in detail the spherical approximation and first-order corrections to the spherical approximation.

Relativistic charged Bose gas

International Nuclear Information System (INIS)

Hines, D.F.; Frankel, N.E.

1979-01-01

The charged Bose has been previously studied as a many body problem of great intrinsic interest which can also serve as a model of some real physical systems, for example, superconductors, white dwarf stars and neutron stars. In this article the excitation spectrum of a relativistic spin-zero charged Bose gas is obtained in a dielectric response formulation. Relativity introduces a dip in the spectrum and consequences of this dip for the thermodynamic functions are discussed

Group theoretical classification of broken symmetry states of the two-fold degenerate Hubbard model on a triangular lattice

International Nuclear Information System (INIS)

Masago, Akira; Suzuki, Naoshi

2001-01-01

By a group theoretical procedure we derive the possible spontaneously broken-symmetry states for the two-fold degenerate Hubbard model on a two-dimensional triangular lattice. For ordering wave vectors corresponding to the points Γ and K in the first BZ we find 22 states which include 16 collinear and six non-collinear states. The collinear states include the usual SDW and CDW states which appear also in the single-band Hubbard model. The non-collinear states include exotic ordering states of orbitals and spins as well as the triangular arrangement of spins

Collision of Bose Condensate Dark Matter structures

International Nuclear Information System (INIS)

Guzman, F. S.

2008-01-01

The status of the scalar field or Bose condensate dark matter model is presented. Results about the solitonic behavior in collision of structures is presented as a possible explanation to the recent-possibly-solitonic behavior in the bullet cluster merger. Some estimates about the possibility to simulate the bullet cluster under the Bose Condensate dark matter model are indicated.

Phase diagram of the Hubbard model with arbitrary band filling: renormalization group approach

International Nuclear Information System (INIS)

Cannas, Sergio A.; Cordoba Univ. Nacional; Tsallis, Constantino.

1991-01-01

The finite temperature phase diagram of the Hubbard model in d = 2 and d = 3 is calculated for arbitrary values of the parameter U/t and chemical potential μ using a quantum real space renormalization group. Evidence for a ferromagnetic phase at low temperatures is presented. (author). 15 refs., 5 figs

Weberized Mumford-Shah Model with Bose-Einstein Photon Noise

International Nuclear Information System (INIS)

Shen Jianhong; Jung, Yoon-Mo

2006-01-01

Human vision works equally well in a large dynamic range of light intensities, from only a few photons to typical midday sunlight. Contributing to such remarkable flexibility is a famous law in perceptual (both visual and aural) psychology and psychophysics known as Weber's Law. The current paper develops a new segmentation model based on the integration of Weber's Law and the celebrated Mumford-Shah segmentation model (Comm. Pure Appl. Math., vol. 42, pp. 577-685, 1989). Explained in detail are issues concerning why the classical Mumford-Shah model lacks light adaptivity, and why its 'weberized' version can more faithfully reflect human vision's superior segmentation capability in a variety of illuminance conditions from dawn to dusk. It is also argued that the popular Gaussian noise model is physically inappropriate for the weberization procedure. As a result, the intrinsic thermal noise of photon ensembles is introduced based on Bose and Einstein's distributions in quantum statistics, which turns out to be compatible with weberization both analytically and computationally. The current paper focuses on both the theory and computation of the weberized Mumford-Shah model with Bose-Einstein noise. In particular, Ambrosio-Tortorelli's Γ-convergence approximation theory is adapted (Boll. Un. Mat. Ital. B, vol. 6, pp. 105-123, 1992), and stable numerical algorithms are developed for the associated pair ofnonlinear Euler-Lagrange PDEs

On the Dynamics of the Fermi-Bose model

DEFF Research Database (Denmark)

Ögren, Magnus

In this talk we formulate and prove results for the exponential matrix representing the dynamics of the Fermi-Bose model in an undepleted bosonic field approximation. A recent application of this model is molecular dimmers dissociating into its atomic compounds. The problem is solved in D spatial....... In particular the results can be used for studies of threedimensional physical systems of arbitrary geometry. We illustrate the generality of our approach by giving numerical results for the dynamics of Glauber type atomic pair correlation functions for a non-isotropic three-dimensional harmonically trapped...

Gross-Pitaevskii equation for Bose particles in a double-well potential: Two-mode models and beyond

International Nuclear Information System (INIS)

Ananikian, D.; Bergeman, T.

2006-01-01

In this work, our primary goal has been to explore the range of validity of two-mode models for Bose-Einstein condensates in double-well potentials. Our derivation, like others, uses symmetric and antisymmetric condensate basis functions for the Gross-Pitaevskii equation. In what we call an 'improved two-mode model' (I2M), the tunneling coupling energy explicitly includes a nonlinear interaction term, which has been given previously in the literature but not widely appreciated. We show that when the atom number (and hence the extent of the wave function) in each well vary appreciably with time, the nonlinear interaction term produces a temporal change in the tunneling energy or rate, which has not previously been considered to our knowledge. In addition, we obtain a parameter, labeled ''interaction tunneling,'' that produces a decrease of the tunneling energy when the wave functions in the two wells overlap to some extent. Especially for larger values of the nonlinear interaction term, results from this model produce better agreement with numerical solutions of the time-dependent Gross-Pitaevskii equation in one and three dimensions, as compared with models that have no interaction term in the tunneling energy. The usefulness of this model is demonstrated by good agreement with recent experimental results for the tunneling oscillation frequency [Albiez et al., Phys. Rev. Lett. 95, 010402 (2005)]. We also present equations and results for a multimode approach, and use the I2M model to obtain modified equations for the second-quantized version of the Bose-Einstein double-well problem

Disorder-Induced Order in Two-Component Bose-Einstein Condensates

International Nuclear Information System (INIS)

Niederberger, A.; Schulte, T.; Wehr, J.; Lewenstein, M.; Sanchez-Palencia, L.; Sacha, K.

2008-01-01

We propose and analyze a general mechanism of disorder-induced order in two-component Bose-Einstein condensates, analogous to corresponding effects established for XY spin models. We show that a random Raman coupling induces a relative phase of π/2 between the two BECs and that the effect is robust. We demonstrate it in one, two, and three dimensions at T=0 and present evidence that it persists at small T>0. Applications to phase control in ultracold spinor condensates are discussed

Relaxation dynamics of a driven two-level system coupled to a Bose-Einstein condensate: application to quantum dot-dipolar exciton gas hybrid systems.

Science.gov (United States)

Kovalev, Vadim M; Tse, Wang-Kong

2017-11-22

We develop a microscopic theory for the relaxation dynamics of an optically pumped two-level system (TLS) coupled to a bath of weakly interacting Bose gas. Using Keldysh formalism and diagrammatic perturbation theory, expressions for the relaxation times of the TLS Rabi oscillations are derived when the boson bath is in the normal state and the Bose-Einstein condensate (BEC) state. We apply our general theory to consider an irradiated quantum dot coupled with a boson bath consisting of a two-dimensional dipolar exciton gas. When the bath is in the BEC regime, relaxation of the Rabi oscillations is due to both condensate and non-condensate fractions of the bath bosons for weak TLS-light coupling and pre dominantly due to the non-condensate fraction for strong TLS-light coupling. Our theory also shows that a phase transition of the bath from the normal to the BEC state strongly influences the relaxation rate of the TLS Rabi oscillations. The TLS relaxation rate is approximately independent of the pump field frequency and monotonically dependent on the field strength when the bath is in the low-temperature regime of the normal phase. Phase transition of the dipolar exciton gas leads to a non-monotonic dependence of the TLS relaxation rate on both the pump field frequency and field strength, providing a characteristic signature for the detection of BEC phase transition of the coupled dipolar exciton gas.

Many-body physics with circuit quantum electrodynamics

International Nuclear Information System (INIS)

Leib, Martin H.

2015-01-01

We present proposals to simulate many-body physics with superconducting circuits. The ''body'' to work with for superconducting circuits is the microwave photon and interaction is induced by the nonlinearity of the Josephson effect. We present two different approaches to simulate Bose-Hubbard physics, one based on a polariton scheme and another with nonlinear resonators. We also present a Dicke-model like simulator for ultrastrongly coupled Josephson junctions to a resonator and show a scheme for implementing long range interactions.

Absence of ballistic charge transport in the half-filled 1D Hubbard model

Science.gov (United States)

Carmelo, J. M. P.; Nemati, S.; Prosen, T.

2018-05-01

Whether in the thermodynamic limit of lattice length L → ∞, hole concentration mηz = - 2 Sηz/L = 1 -ne → 0, nonzero temperature T > 0, and U / t > 0 the charge stiffness of the 1D Hubbard model with first neighbor transfer integral t and on-site repulsion U is finite or vanishes and thus whether there is or there is no ballistic charge transport, respectively, remains an unsolved and controversial issue, as different approaches yield contradictory results. (Here Sηz = - (L -Ne) / 2 is the η-spin projection and ne =Ne / L the electronic density.) In this paper we provide an upper bound on the charge stiffness and show that (similarly as at zero temperature), for T > 0 and U / t > 0 it vanishes for mηz → 0 within the canonical ensemble in the thermodynamic limit L → ∞. Moreover, we show that at high temperature T → ∞ the charge stiffness vanishes as well within the grand-canonical ensemble for L → ∞ and chemical potential μ →μu where (μ -μu) ≥ 0 and 2μu is the Mott-Hubbard gap. The lack of charge ballistic transport indicates that charge transport at finite temperatures is dominated by a diffusive contribution. Our scheme uses a suitable exact representation of the electrons in terms of rotated electrons for which the numbers of singly occupied and doubly occupied lattice sites are good quantum numbers for U / t > 0. In contrast to often less controllable numerical studies, the use of such a representation reveals the carriers that couple to the charge probes and provides useful physical information on the microscopic processes behind the exotic charge transport properties of the 1D electronic correlated system under study.

Heisenberg magnetic chain with single-ion easy-plane anisotropy: Hubbard operators approach

International Nuclear Information System (INIS)

Spirin, D.V.; Fridman, Y.A.

2003-01-01

We investigate the gap in excitation spectrum of one-dimensional S=1 ferro- and antiferromagnets with easy-plane single-ion anisotropy. The self-consistent modification of Hubbard operators approach which enables to account single-site term exactly is used. For antiferromagnetic model we found Haldane phase that exists up to point D=4J (where D is anisotropy parameter, J is exchange coupling), while quadrupolar phase realizes at larger values of anisotropy. Our results specify those of Golinelli et al. (Phys. Rev. B. 45 (1992) 9798), where similar model was studied. Besides the method gives gap value closer to numerical estimations than usual spin-wave theories

Control of the dynamics of coupled atomic-molecular Bose-Einstein condensates: Modified Gross-Pitaevskii approach

International Nuclear Information System (INIS)

Gupta, Moumita; Dastidar, Krishna Rai

2009-01-01

We study the dynamics of the atomic and molecular Bose-Einstein condensates (BECs) of 87 Rb in a spherically symmetric trap coupled by stimulated Raman photoassociation process. Considering the higher order nonlinearity in the atom-atom interaction we analyze the dynamics of the system using coupled modified Gross-Pitaevskii (MGP) equations and compare it with mean-field coupled Gross-Pitaevskii (GP) dynamics. Considerable differences in the dynamics are obtained in these two approaches at large scattering length, i.e., for large values of peak-gas parameter x pk ≥10 -3 . We show how the dynamics of the coupled system is affected when the atom-molecule and molecule-molecule interactions are considered together with the atom-atom interaction and also when the strengths of these three interactions are increased. The effect of detuning on the efficiency of conversion of atomic fractions into molecules is demonstrated and the feasibility of maximum molecular BEC formation by varying the Raman detuning parameter at different values of time is explored. Thus by varying the Raman detuning and the scattering length for atom-atom interaction one can control the dynamics of the coupled atomic-molecular BEC system. We have also solved coupled Gross-Pitaevskii equations for atomic to molecular condensate formation through magnetic Feshbach resonance in a BEC of 85 Rb. We found similar features for oscillations between atomic and molecular condensates noted in previous theoretical study and obtained fairly good agreement with the evolution of total atomic condensate observed experimentally.

Role of spin-orbit coupling in the Kugel-Khomskii model on the honeycomb lattice

Science.gov (United States)

Koga, Akihisa; Nakauchi, Shiryu; Nasu, Joji

2018-03-01

We study the effective spin-orbital model for honeycomb-layered transition metal compounds, applying the second-order perturbation theory to the three-orbital Hubbard model with the anisotropic hoppings. This model is reduced to the Kitaev model in the strong spin-orbit coupling limit. Combining the cluster mean-field approximations with the exact diagonalization, we treat the Kugel-Khomskii type superexchange interaction and spin-orbit coupling on an equal footing to discuss ground-state properties. We find that a zigzag ordered state is realized in the model within nearest-neighbor interactions. We clarify how the ordered state competes with the nonmagnetic state, which is adiabatically connected to the quantum spin liquid state realized in a strong spin-orbit coupling limit. Thermodynamic properties are also addressed. The present paper should provide another route to account for the Kitaev-based magnetic properties in candidate materials.

Fermi surface of the one-dimensional Hubbard model. Finite-size effects

Energy Technology Data Exchange (ETDEWEB)

Bourbonnais, C.; Nelisse, H.; Reid, A.; Tremblay, A.M.S. (Dept. de Physique and Centre de Recherche en Physique du Solide (C.R.P.S.), Univ. de Sherbrooke, Quebec (Canada))

1989-12-01

The results reported here, using a standard numerical algorithm and a simple low temperature extrapolation, appear consistent with numerical results of Sorella et al. for the one-dimensional Hubbard model in the half-filled and quarter-filled band cases. However, it is argued that the discontinuity at the Fermi level found in the quarter-filled case is likely to come from the zero-temperature finite-size dependence of the quasiparticle weight Z, which is also discussed here. (orig.).

Anindita Bose

Indian Academy of Sciences (India)

Home; Journals; Resonance – Journal of Science Education. Anindita Bose. Articles written in Resonance – Journal of Science Education. Volume 6 Issue 11 November 2001 pp 18-26 General Article. Necklaces, Periodic Points and Permutation Representations - Fermat's Little Theorem · Somnath Basu Anindita Bose ...

Rigorous derivation of the mean-field green functions of the two-band Hubbard model of superconductivity

International Nuclear Information System (INIS)

Adam, G.; Adam, S.

2007-01-01

The Green function (GF) equation of motion technique for solving the effective two-band Hubbard model of high-T c superconductivity in cuprates rests on the Hubbard operator (HO) algebra. We show that, if we take into account the invariance to translations and spin reversal, the HO algebra results in invariance properties of several specific correlation functions. The use of these properties allows rigorous derivation and simplification of the expressions of the frequency matrix (FM) and of the generalized mean-field approximation (GMFA) Green functions (GFs) of the model. For the normal singlet hopping and anomalous exchange pairing correlation functions which enter the FM and GMFA-GFs, the use of spectral representations allows the identification and elimination of exponentially small quantities. This procedure secures the reduction of the correlation order to the GMFA-GF expressions

Ferromagnetism in the Hubbard model: a modified perturbation theory

International Nuclear Information System (INIS)

Gangadhar Reddy, G.; Ramakanth, A.; Nolting, W.

2005-01-01

We study the possibility of ferromagnetism in the Hubbard model using the modified perturbation theory. In this approach an Ansatz is made for the self-energy of the electron which contains the second order contribution developed around the Hartree-Fock solution and two parameters. The parameters are fixed by using a moment method. This self energy satisfies several known exact limiting cases. Using this self energy, the Curie temperature T c as a function of band filling n is investigated. It is found that T c falls off abruptly as n approaches half filling. The results are in qualitative agreement with earlier calculations using other approximation schemes. (author)

Filling-driven Mott transition in SU(N ) Hubbard models

Science.gov (United States)

Lee, Seung-Sup B.; von Delft, Jan; Weichselbaum, Andreas

2018-04-01

We study the filling-driven Mott transition involving the metallic and paramagnetic insulating phases in SU (N ) Fermi-Hubbard models, using the dynamical mean-field theory and the numerical renormalization group as its impurity solver. The compressibility shows a striking temperature dependence: near the critical end-point temperature, it is strongly enhanced in the metallic phase close to the insulating phase. We demonstrate that this compressibility enhancement is associated with the thermal suppression of the quasiparticle peak in the local spectral functions. We also explain that the asymmetric shape of the quasiparticle peak originates from the asymmetry in the dynamics of the generalized doublons and holons.

Bose-Einstein condensates in atomic gases: simple theoretical results

International Nuclear Information System (INIS)

Castin, Y.

2001-01-01

The author presents the theory of the Bose-Einstein condensation along with a discussion of experimental tests. The author deals successively with the following topics: - the ideal Bose gas in a trap (first in a harmonic trap and then in a more general trap), - a model for the atomic interaction, - interacting Bose gas in the Hartree-Fock approximation, - properties of the condensate wavefunction, - the Gross-Pitaevskii equation, - Bogoliubov approach and thermodynamical stability, - phase coherence properties at the Bose-Einstein condensate, and - symmetry-breaking description of condensates. (A.C.)

Bose-Einstein condensation in an ultra-hot gas of pumped magnons.

Science.gov (United States)

Serga, Alexander A; Tiberkevich, Vasil S; Sandweg, Christian W; Vasyuchka, Vitaliy I; Bozhko, Dmytro A; Chumak, Andrii V; Neumann, Timo; Obry, Björn; Melkov, Gennadii A; Slavin, Andrei N; Hillebrands, Burkard

2014-03-11

Bose-Einstein condensation of quasi-particles such as excitons, polaritons, magnons and photons is a fascinating quantum mechanical phenomenon. Unlike the Bose-Einstein condensation of real particles (like atoms), these processes do not require low temperatures, since the high densities of low-energy quasi-particles needed for the condensate to form can be produced via external pumping. Here we demonstrate that such a pumping can create remarkably high effective temperatures in a narrow spectral region of the lowest energy states in a magnon gas, resulting in strikingly unexpected transitional dynamics of Bose-Einstein magnon condensate: the density of the condensate increases immediately after the external magnon flow is switched off and initially decreases if it is switched on again. This behaviour finds explanation in a nonlinear 'evaporative supercooling' mechanism that couples the low-energy magnons overheated by pumping with all the other thermal magnons, removing the excess heat, and allowing Bose-Einstein condensate formation.

Bose-Einstein condensation of a relativistic Bose gas trapped in a general external potential

International Nuclear Information System (INIS)

Su Guozhen; Chen Jincan; Chen Lixuan

2006-01-01

Bose-Einstein condensation of an ideal relativistic Bose gas trapped in a generic power-law potential is investigated. The analytical expressions for some important parameters such as the critical temperature, ground-state fraction and heat capacity are derived. The general criteria on the occurrence of Bose-Einstein condensation and the discontinuity of heat capacity at the critical temperature are obtained. The results obtained here present a unified description for the Bose-Einstein condensation of a class of ideal Bose systems so that many important conclusions in the literature are included in this paper

Collective Kondo effect in the Anderson-Hubbard lattice

Science.gov (United States)

Fazekas, P.; Itai, K.

1997-02-01

The periodic Anderson model is extended by switching on a Hubbard U for the conduction electrons. We use the Gutzwiller variational method to study the nearly integral valent limit. The lattice Kondo energy contains the U-dependent chemical potential of the Hubbard subsystem in the exponent, and the correlation-induced band narrowing in the prefactor. Both effects tend to suppress the Kondo scale, which can be understood to result from the blocking of hybridization. At half-filling, we find a Brinkman-Rice-type transition from a Kondo insulator to a Mott insulator.

Unified one-band Hubbard model for magnetic and electronic spectra of the parent compounds of cuprate superconductors

Science.gov (United States)

Dalla Piazza, B.; Mourigal, M.; Guarise, M.; Berger, H.; Schmitt, T.; Zhou, K. J.; Grioni, M.; Rønnow, H. M.

2012-03-01

Using low-energy projection of the one-band t-t'-t'' Hubbard model we derive an effective spin Hamiltonian and its spin-wave expansion to order 1/S. We fit the spin-wave dispersion of several parent compounds to the high-temperature superconducting cuprates La2CuO4, Sr2CuO2Cl2, and Bi2Sr2YCu2O8. Our accurate quantitative determination of the one-band Hubbard model parameters allows prediction and comparison to experimental results. Among those we discuss the two-magnon Raman peak line shape, the K-edge resonant inelastic x-ray scattering 500-meV peak, and the high-energy kink in the angle-resolved photoemission spectroscopy quasiparticle dispersion, also known as the waterfall feature.

Critical, statistical, and thermodynamical properties of lattice models

Energy Technology Data Exchange (ETDEWEB)

Varma, Vipin Kerala

2013-10-15

In this thesis we investigate zero temperature and low temperature properties - critical, statistical and thermodynamical - of lattice models in the contexts of bosonic cold atom systems, magnetic materials, and non-interacting particles on various lattice geometries. We study quantum phase transitions in the Bose-Hubbard model with higher body interactions, as relevant for optical lattice experiments of strongly interacting bosons, in one and two dimensions; the universality of the Mott insulator to superfluid transition is found to remain unchanged for even large three body interaction strengths. A systematic renormalization procedure is formulated to fully re-sum these higher (three and four) body interactions into the two body terms. In the strongly repulsive limit, we analyse the zero and low temperature physics of interacting hard-core bosons on the kagome lattice at various fillings. Evidence for a disordered phase in the Ising limit of the model is presented; in the strong coupling limit, the transition between the valence bond solid and the superfluid is argued to be first order at the tip of the solid lobe.

Critical, statistical, and thermodynamical properties of lattice models

International Nuclear Information System (INIS)

Varma, Vipin Kerala

2013-10-01

In this thesis we investigate zero temperature and low temperature properties - critical, statistical and thermodynamical - of lattice models in the contexts of bosonic cold atom systems, magnetic materials, and non-interacting particles on various lattice geometries. We study quantum phase transitions in the Bose-Hubbard model with higher body interactions, as relevant for optical lattice experiments of strongly interacting bosons, in one and two dimensions; the universality of the Mott insulator to superfluid transition is found to remain unchanged for even large three body interaction strengths. A systematic renormalization procedure is formulated to fully re-sum these higher (three and four) body interactions into the two body terms. In the strongly repulsive limit, we analyse the zero and low temperature physics of interacting hard-core bosons on the kagome lattice at various fillings. Evidence for a disordered phase in the Ising limit of the model is presented; in the strong coupling limit, the transition between the valence bond solid and the superfluid is argued to be first order at the tip of the solid lobe.

Phase diagram and re-entrant fermionic entanglement in a hybrid Ising-Hubbard ladder

Science.gov (United States)

Sousa, H. S.; Pereira, M. S. S.; de Oliveira, I. N.; Strečka, J.; Lyra, M. L.

2018-05-01

The degree of fermionic entanglement is examined in an exactly solvable Ising-Hubbard ladder, which involves interacting electrons on the ladder's rungs described by Hubbard dimers at half-filling on each rung, accounting for intrarung hopping and Coulomb terms. The coupling between neighboring Hubbard dimers is assumed to have an Ising-like nature. The ground-state phase diagram consists of four distinct regions corresponding to the saturated paramagnetic, the classical antiferromagnetic, the quantum antiferromagnetic, and the mixed classical-quantum phase. We have exactly computed the fermionic concurrence, which measures the degree of quantum entanglement between the pair of electrons on the ladder rungs. The effects of the hopping amplitude, the Coulomb term, temperature, and magnetic fields on the fermionic entanglement are explored in detail. It is shown that the fermionic concurrence displays a re-entrant behavior when quantum entanglement is being generated at moderate temperatures above the classical saturated paramagnetic ground state.

Bose-Einstein condensation and indirect excitons: a review.

Science.gov (United States)

Combescot, Monique; Combescot, Roland; Dubin, François

2017-06-01

We review recent progress on Bose-Einstein condensation (BEC) of semiconductor excitons. The first part deals with theory, the second part with experiments. This Review is written at a time where the problem of exciton Bose-Einstein condensation has just been revived by the understanding that the exciton condensate must be dark because the exciton ground state is not coupled to light. Here, we theoretically discuss this missed understanding before providing its experimental support through experiments that scrutinize indirect excitons made of spatially separated electrons and holes. The theoretical part first discusses condensation of elementary bosons. In particular, the necessary inhibition of condensate fragmentation by exchange interaction is stressed, before extending the discussion to interacting bosons with spin degrees of freedom. The theoretical part then considers composite bosons made of two fermions like semiconductor excitons. The spin structure of the excitons is detailed, with emphasis on the crucial fact that ground-state excitons are dark: indeed, this imposes the exciton Bose-Einstein condensate to be not coupled to light in the dilute regime. Condensate fragmentations are then reconsidered. In particular, it is shown that while at low density, the exciton condensate is fully dark, it acquires a bright component, coherent with the dark one, beyond a density threshold: in this regime, the exciton condensate is 'gray'. The experimental part first discusses optical creation of indirect excitons in quantum wells, and the detection of their photoluminescence. Exciton thermalisation is also addressed, as well as available approaches to estimate the exciton density. We then switch to specific experiments where indirect excitons form a macroscopic fragmented ring. We show that such ring provides efficient electrostatic trapping in the region of the fragments where an essentially-dark exciton Bose-Einstein condensate is formed at sub-Kelvin bath

Polaronic and bipolaronic structures in the adiabatic Hubbard-Hostein model involving 2 electrons and in its extensions; Structures polaroniques et bipolaroniques dans le modele de hostein hubbard adiabatique a deux electrons et ses extensions

Energy Technology Data Exchange (ETDEWEB)

Proville, L

1998-03-30

This thesis brings its contribution to the bipolaronic theory which might explain the origin of superconductivity at high temperature. A polaron is a quasiparticle made up of a localized electron and a deformation in the crystal structure. 2 electrons in singlet states localized on the same site form a bipolaron. Whenever the Coulomb repulsion between the 2 electrons is too strong bipolaron turns into 2 no bound polarons. We study the existence and the mobility of bipolarons. We describe the electron-phonon interaction by the Holstein term and the Coulomb repulsion by the Hubbard term. 2 assumptions are made: - the local electron-phonon interaction is strong and opposes the Coulomb repulsion between Hubbard type electrons - the system is close to the adiabatic limit. The system is reduced to 2 electrons in order to allow an exact treatment and the investigation of some bipolaronic bound states. At 2-dimensions the existence of bipolarons requires a very strong coupling which forbids any classical mobility. In some cases an important tunneling effect appears and we show that mobile bipolarons exist in a particular parameter range. Near the adiabatic limit we prove that polaronic and bipolaronic structures exist for a great number of electrons. (A.C.) 33 refs.

Hole-hole correlations in the U=∞ limit of the Hubbard model and the stability of the Nagaoka state

International Nuclear Information System (INIS)

Long, M.W.; Zotos, X.

1993-01-01

We use exact diagonalization in order to study the infinite-U limit of the two-dimensional Hubbard model. As well as looking at single-particle correlations, such as n kσ =left-angle c kσ † c kσ right-angle, we also study N-particle correlation functions, which compare the relative positions of all the particles in different models. In particular we study 16- and 18-site clusters and compare the charge correlations in the Hubbard model with those of spinless fermions and hard-core bosons. We find that although low densities of holes favor a ''locally ferromagnetic'' fermionic description, the correlations at larger densities resemble those of pure hard-core bosons surprisingly well

Bose condensates make quantum leaps and bounds

International Nuclear Information System (INIS)

Castin, Y.; Dum, R.; Sinatra, A.

1999-01-01

Since the first observation in 1995 of Bose-Einstein condensation in dilute atomic gases, atomic physicists have made extraordinary progress in understanding this unusual quantum state of matter. BOSE-EINSTEIN condensation is a macroscopic quantum phenomenon that was first predicted by Albert Einstein in the 1920s, at a time when quantum theory was still developing and was being applied to microscopic systems, such as individual particles and atoms. Einstein applied the new concept of Bose statistics to an ideal gas of identical atoms that were at thermal equilibrium and trapped in a box. He predicted that at sufficiently low temperatures the particles would accumulate in the lowest quantum state in the box, giving rise to a new state of matter with many unusual properties. The crucial point of Einstein's model is the absence of interactions between the particles in the box. However, this makes his prediction difficult to test in practice. In most real systems the complicating effect of particle interactions causes the gas to solidify well before the temperature for Bose-Einstein condensation is reached. But techniques developed in the past four years have allowed physicists to form Bose-Einstein condensates for a wide range of elements. In this article the authors describe the latest advances in Bose-Einstein condensation. (UK)

Coexistence of incommensurate magnetism and superconductivity in the two-dimensional Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Yamase, Hiroyuki [Max Planck Institute for Solid State Research, Stuttgart (Germany); National Institute for Materials Science, Tsukuba (Japan); Eberlein, Andreas [Max Planck Institute for Solid State Research, Stuttgart (Germany); Department of Physics, Harvard University, Cambridge (United States); Metzner, Walter [Max Planck Institute for Solid State Research, Stuttgart (Germany)

2016-07-01

We analyze the competition of magnetism and superconductivity in the two-dimensional Hubbard model with a moderate interaction strength, including the possibility of incommensurate spiral magnetic order. Using an unbiased renormalization group approach, we compute magnetic and superconducting order parameters in the ground state. In addition to previously established regions of Neel order coexisting with d-wave superconductivity, the calculations reveal further coexistence regions where superconductivity is accompanied by incommensurate magnetic order.

Intersite electron correlations in a Hubbard model on inhomogeneous lattices

International Nuclear Information System (INIS)

Takemori, Nayuta; Koga, Akihisa; Hafermann, Hartmut

2016-01-01

We study intersite electron correlations in the half-filled Hubbard model on square lattices with periodic and open boundary conditions by means of a real-space dual fermion approach. By calculating renormalization factors, we clarify that nearest-neighbor intersite correlations already significantly reduce the critical interaction. The Mott transition occurs at U/t ∼ 6.4, where U is the interaction strength and t is the hopping integral. This value is consistent with quantum Monte Carlo results. It shows the importance of short-range intersite correlations, which are taken into account in the framework of the real-space dual fermion approach. (paper)

Edge-Corrected Mean-Field Hubbard Model: Principle and Applications in 2D Materials

Directory of Open Access Journals (Sweden)

Xi Zhang

2017-05-01

Full Text Available This work reviews the current progress of tight-binding methods and the recent edge-modified mean-field Hubbard model. Undercoordinated atoms (atoms not fully coordinated exist at a high rate in nanomaterials with their impact overlooked. A quantum theory was proposed to calculate electronic structure of nanomaterials by incorporating bond order-length-strength (BOLS correlation to mean-field Hubbard model, i.e., BOLS-HM. Consistency between the BOLS-HM calculation and density functional theory (DFT calculation on 2D materials verified that (i bond contractions and potential well depression occur at the edge of graphene, phosphorene, and antimonene nanoribbons; (ii the physical origin of the band gap opening of graphene, phosphorene, and antimonene nanoribbons lays in the enhancement of edge potentials and hopping integrals due to the shorter and stronger bonds between undercoordinated atoms; (iii the band gap of 2D material nanoribbons expand as the width decreases due to the increasing under-coordination effects of edges which modulates the conductive behaviors; and (iv non-bond electrons at the edges and atomic vacancies of 2D material accompanied with the broken bond contribute to the Dirac-Fermi polaron (DFP with a local magnetic moment.

Bose-Einstein correlation in the Lund model

International Nuclear Information System (INIS)

Anderson, B.

1998-01-01

I will present the Lund Model fragmentation in a somewhat different way than what is usually done. It is true that the formulas are derived from (semi-)classical probability arguments, but they can be motivated in a quantum mechanical setting and it is in particular possible to derive a transition matrix element. I will present two scenarios, one based upon Schwinger tunneling and one upon Wilson loop operators. The results will coincide and throw some light upon the sizes of the three main phenomenological parameters which occur in the Lund Model. After that I will show that in this way it is possible to obtain a model for the celebrated Bose-Einstein correlations between two bosons with small relative momenta. This model will exhibit non-trivial two- and three-particle BE correlations, influence the observed p-spectrum and finally be different for charged and neutral pion correlations. (author)

Phase diagram of 2D Hubbard model by simulated annealing mean field approximation

International Nuclear Information System (INIS)

Kato, Masaru; Kitagaki, Takashi

1991-01-01

In order to investigate the stable magnetic structure of the Hubbard model on a square lattice, we utilize the dynamical simulated annealing method which proposed by R. Car and M. Parrinello. Results of simulations on a 10 x 10 lattice system with 80 electrons under assumption of collinear magnetic structure that the most stable state is incommensurate spin density wave state with periodic domain wall. (orig.)

Pairing and condensation in a resonant Bose-Fermi mixture

International Nuclear Information System (INIS)

Fratini, Elisa; Pieri, Pierbiagio

2010-01-01

We study by diagrammatic means a Bose-Fermi mixture, with boson-fermion coupling tuned by a Fano-Feshbach resonance. For increasing coupling, the growing boson-fermion pairing correlations progressively reduce the boson condensation temperature and make it eventually vanish at a critical coupling. Such quantum critical point depends very weakly on the population imbalance and, for vanishing boson densities, coincides with that found for the polaron-molecule transition in a strongly imbalanced Fermi gas, thus bridging two quite distinct physical systems.

A Bose-Einstein model of particle multiplicity distributions

Energy Technology Data Exchange (ETDEWEB)

Mekjian, A.Z. [Department of Physics and Astronomy, Rutgers University, Piscataway, NJ 08854 (United States) and California Institute of Technology, Kellogg Radiation Lab., Pasadena, CA 91106 (United States) and MTA KFKI RMKI, 114 PO Box 49, H-1525 Budapest (Hungary)]. E-mail: amekjian@physics.rutgers.edu; Csoergoe, T. [MTA KFKI RMKI, 114 PO Box 49, H-1525 Budapest (Hungary); Hegyi, S. [MTA KFKI RMKI, 114 PO Box 49, H-1525 Budapest (Hungary)

2007-03-01

A model of particle production is developed based on a parallel with a theory of Bose-Einstein condensation and similarities with other critical phenomena such as critical opalescence. The role of a power law critical exponent {tau} and Levy index {alpha} are studied. Various features of this model are developed and compared with other commonly used models of particle production which are shown to differ by having different values for {tau}, {alpha}. While void scaling is a feature of this model, hierarchical structure is not a general property of it. The value of the exponent {tau}=2 is a transition point associated with void and hierarchical scaling features. An exponent {gamma} is introduced to describe enhanced fluctuations near a critical point. Experimentally determined properties of the void scaling function can be used to determine {tau}.

A Bose-Einstein model of particle multiplicity distributions

International Nuclear Information System (INIS)

Mekjian, A.Z.; Csoergoe, T.; Hegyi, S.

2007-01-01

A model of particle production is developed based on a parallel with a theory of Bose-Einstein condensation and similarities with other critical phenomena such as critical opalescence. The role of a power law critical exponent τ and Levy index α are studied. Various features of this model are developed and compared with other commonly used models of particle production which are shown to differ by having different values for τ, α. While void scaling is a feature of this model, hierarchical structure is not a general property of it. The value of the exponent τ=2 is a transition point associated with void and hierarchical scaling features. An exponent γ is introduced to describe enhanced fluctuations near a critical point. Experimentally determined properties of the void scaling function can be used to determine τ

A Bose Einstein model of particle multiplicity distributions

Science.gov (United States)

Mekjian, A. Z.; Csörgö, T.; Hegyi, S.

2007-03-01

A model of particle production is developed based on a parallel with a theory of Bose-Einstein condensation and similarities with other critical phenomena such as critical opalescence. The role of a power law critical exponent τ and Levy index α are studied. Various features of this model are developed and compared with other commonly used models of particle production which are shown to differ by having different values for τ, α. While void scaling is a feature of this model, hierarchical structure is not a general property of it. The value of the exponent τ=2 is a transition point associated with void and hierarchical scaling features. An exponent γ is introduced to describe enhanced fluctuations near a critical point. Experimentally determined properties of the void scaling function can be used to determine τ.

Two-particle excitations in the Hubbard model for high-temperature superconductors. A quantum cluster study

International Nuclear Information System (INIS)

Brehm, Sascha

2009-01-01

Two-particle excitations, such as spin and charge excitations, play a key role in high-T c cuprate superconductors (HTSC). Due to the antiferromagnetism of the parent compound the magnetic excitations are supposed to be directly related to the mechanism of superconductivity. In particular, the so-called resonance mode is a promising candidate for the pairing glue, a bosonic excitation mediating the electronic pairing. In addition, its interactions with itinerant electrons may be responsible for some of the observed properties of HTSC. Hence, getting to the bottom of the resonance mode is crucial for a deeper understanding of the cuprate materials. To analyze the corresponding two-particle correlation functions we develop in the present thesis a new, non-perturbative and parameter-free technique for T=0 which is based on the Variational Cluster Approach (VCA, an embedded cluster method for one-particle Green's functions). Guided by the spirit of the VCA we extract an effective electron-hole vertex from an isolated cluster and use a fully renormalized bubble susceptibility χ 0 including the VCA one-particle propagators. Within our new approach, the magnetic excitations of HTSC are shown to be reproduced for the Hubbard model within the relevant strong-coupling regime. Exceptionally, the famous resonance mode occurring in the underdoped regime within the superconductivity-induced gap of spin-flip electron-hole excitations is obtained. Its intensity and hourglass dispersion are in good overall agreement with experiments. Furthermore, characteristic features such as the position in energy of the resonance mode and the difference of the imaginary part of the susceptibility in the superconducting and the normal states are in accord with Inelastic Neutron Scattering (INS) experiments. For the first time, a strongly-correlated parameter-free calculation revealed these salient magnetic properties supporting the S=1 magnetic exciton scenario for the resonance mode. Besides

Correlation effects of third-order perturbation in the extended Hubbard model

International Nuclear Information System (INIS)

Wei, G.Z.; Nie, H.Q.; Li, L.; Zhang, K.Y.

1989-01-01

Using the local approach, a third-order perturbation calculation has been performed to investigate the effects of intra-atomic electron correlation and electron and spin correlation between nearest neighbour sites in the extended Hubbard model. It was found that significant correction of the third order over the second order results and, in comparison with the results of the third-order perturbation where only the intra-atomic electron correlation is included, the influence of the electron and spin correlation between nearest neighbour sites on the correlation energy is non-negligible. 17 refs., 3 figs

Bose-Einstein condensation of paraxial light

Science.gov (United States)

Klaers, J.; Schmitt, J.; Damm, T.; Vewinger, F.; Weitz, M.

2011-10-01

Photons, due to the virtually vanishing photon-photon interaction, constitute to very good approximation an ideal Bose gas, but owing to the vanishing chemical potential a (free) photon gas does not show Bose-Einstein condensation. However, this is not necessarily true for a lower-dimensional photon gas. By means of a fluorescence induced thermalization process in an optical microcavity one can achieve a thermal photon gas with freely adjustable chemical potential. Experimentally, we have observed thermalization and subsequently Bose-Einstein condensation of the photon gas at room temperature. In this paper, we give a detailed description of the experiment, which is based on a dye-filled optical microcavity, acting as a white-wall box for photons. Thermalization is achieved in a photon number-conserving way by photon scattering off the dye molecules, and the cavity mirrors both provide an effective photon mass and a confining potential-key prerequisites for the Bose-Einstein condensation of photons. The experimental results are in good agreement with both a statistical and a simple rate equation model, describing the properties of the thermalized photon gas.

Progress towards localization in the attractive Hubbard model

Science.gov (United States)

Morong, W.; Xu, W.; Demarco, B.

2017-04-01

The interplay between fermionic superfluidity and disorder is a topic of long-standing interest that has recently come within reach of ultracold gas experiments. Outstanding questions include the fate of Cooper pairs in a localized superfluid and the effect of disorder on the superfluid transition temperature. We report progress on tackling this problem using a realization of the Hubbard model with attractive interactions. Our system consists of two spin states of fermionic potassium-40 trapped in a cubic optical lattice. Disorder is introduced using an optical speckle potential, and interactions are controlled via a Feshbach resonance. We study the binding and unbinding of Cooper pairs in this system using rf spectroscopy, changes in Tc by measuring the condensate fraction, and transport properties by observing the response to an applied impulse. We will discuss progress towards these measurements.

Particle-Hole Character of the Higgs and Goldstone Modes in Strongly Interacting Lattice Bosons

Science.gov (United States)

Di Liberto, M.; Recati, A.; Trivedi, N.; Carusotto, I.; Menotti, C.

2018-02-01

We study the low-energy excitations of the Bose-Hubbard model in the strongly interacting superfluid phase using a Gutzwiller approach. We extract the single-particle and single-hole excitation amplitudes for each mode and report emergent mode-dependent particle-hole symmetry on specific arc-shaped lines in the phase diagram connecting the well-known Lorentz-invariant limits of the Bose-Hubbard model. By tracking the in-phase particle-hole symmetric oscillations of the order parameter, we provide an answer to the long-standing question about the fate of the pure amplitude Higgs mode away from the integer-density critical point. Furthermore, we point out that out-of-phase symmetric oscillations in the gapless Goldstone mode are responsible for a full suppression of the condensate density oscillations. Possible detection protocols are also discussed.

Bose, Prof. Indrani

Indian Academy of Sciences (India)

Home; Fellowship. Fellow Profile. Elected: 2000 Section: Physics. Bose, Prof. Indrani Ph.D. (Calcutta), FNASc. Date of birth: 15 August 1951. Specialization: Theoretical Condensed Matter Physics, Statistical Physics, Biological Physics and Systems Biology Address: Emeritus Scientist, Department of Physics, Bose Institute, ...

Distinct solutions of infinite U Hubbard model through nested Bethe ansatz and Gutzwiller projection operator approach

International Nuclear Information System (INIS)

Mishra, A.K.; Kishore, R.

2009-01-01

The exact nested Bethe ansatz solution for the one dimensional (1-D) U infinity Hubbard model show that the state vectors are a product of spin-less fermion and spin wavefunctions, or an appropriate superposition of such factorized wavefunctions. The spin-less fermion component of the wavefunctions ensures no double occupancy at any site. It had been demonstrated that the nested Bethe ansatz wavefunctions in the U infinity limit obey orthofermi statistics. Gutzwiller projection operator formalism is the another well known technique employed to handle U infinity Hubbard model. In general, this approach does not lead to spin-less fermion wavefunctions. Therefore, the nested Bethe ansatz and Gutzwiller projection operator approach give rise to different kinds of the wavefunctions for the U infinity limit of 1-D Hubbard Hamiltonian. To compare the consequences of this dissimilarity in the wavefunctions, we have obtained the ground state energy of a finite system consisting of three particles on a four site closed chain. It is shown that in the nested Bethe ansatz implemented through orthofermion algebra, all the permissible 2 3 spin configurations are degenerate in the ground state. This eight fold degeneracy of the ground state is absent in the Gutzwiller projection operator approach. This finding becomes relevant in the context of known exact U infinity results, which require that all the energy levels are 2 N -fold degenerate for an N particle system.

Bose-Einstein correlations in W-pair decays

CERN Document Server

Barate, R; Ghez, P; Goy, C; Jézéquel, S; Lees, J P; Martin, F; Merle, E; Minard, M N; Pietrzyk, B; Alemany, R; Bravo, S; Casado, M P; Chmeissani, M; Crespo, J M; Fernández, E; Fernández-Bosman, M; Garrido, L; Graugès-Pous, E; Juste, A; Martínez, M; Merino, G; Miquel, R; Mir, L M; Morawitz, P; Pacheco, A; Riu, I; Ruiz, H; Colaleo, A; Creanza, D; De Palma, M; Iaselli, Giuseppe; Maggi, G; Maggi, M; Nuzzo, S; Ranieri, A; Raso, G; Ruggieri, F; Selvaggi, G; Silvestris, L; Tempesta, P; Tricomi, A; Zito, G; Huang, X; Lin, J; Ouyang, Q; Wang, T; Xie, Y; Xu, R; Xue, S; Zhang, J; Zhang, L; Zhao, W; Abbaneo, D; Boix, G; Buchmüller, O L; Cattaneo, M; Cerutti, F; Ciulli, V; Davies, G; Dissertori, G; Drevermann, H; Forty, Roger W; Frank, M; Gianotti, F; Greening, T C; Halley, A W; Hansen, J B; Harvey, J; Janot, P; Jost, B; Kado, M; Leroy, O; Maley, P; Mato, P; Minten, Adolf G; Moutoussi, A; Ranjard, F; Rolandi, Luigi; Schlatter, W D; Schmitt, M; Schneider, O; Spagnolo, P; Tejessy, W; Teubert, F; Tournefier, E; Valassi, Andrea; Wright, A E; Ajaltouni, Ziad J; Badaud, F; Chazelle, G; Deschamps, O; Dessagne, S; Falvard, A; Ferdi, C; Gay, P; Guicheney, C; Henrard, P; Jousset, J; Michel, B; Monteil, S; Montret, J C; Pallin, D; Pascolo, J M; Perret, P; Podlyski, F; Hansen, J D; Hansen, J R; Hansen, P H; Nilsson, B S; Rensch, B; Wäänänen, A; Daskalakis, G; Kyriakis, A; Markou, C; Simopoulou, Errietta; Vayaki, Anna; Blondel, A; Brient, J C; Machefert, F P; Rougé, A; Swynghedauw, M; Tanaka, R; Videau, H L; Focardi, E; Parrini, G; Zachariadou, K; Corden, M; Georgiopoulos, C H; Antonelli, A; Bencivenni, G; Bologna, G; Bossi, F; Campana, P; Capon, G; Chiarella, V; Laurelli, P; Mannocchi, G; Murtas, F; Murtas, G P; Passalacqua, L; Pepé-Altarelli, M; Chalmers, M; Kennedy, J; Lynch, J G; Negus, P; O'Shea, V; Räven, B; Smith, D; Teixeira-Dias, P; Thompson, A S; Ward, J J; Cavanaugh, R J; Dhamotharan, S; Geweniger, C; Hanke, P; Hepp, V; Kluge, E E; Leibenguth, G; Putzer, A; Tittel, K; Werner, S; Wunsch, M; Beuselinck, R; Binnie, David M; Cameron, W; Dornan, Peter J; Girone, M; Goodsir, S M; Marinelli, N; Martin, E B; Nash, J; Nowell, J; Przysiezniak, H; Sciabà, A; Sedgbeer, J K; Thompson, J C; Thomson, E; Williams, M D; Ghete, V M; Girtler, P; Kneringer, E; Kuhn, D; Rudolph, G; Bowdery, C K; Buck, P G; Ellis, G; Finch, A J; Foster, F; Hughes, G; Jones, R W L; Robertson, N A; Smizanska, M; Williams, M I; Giehl, I; Hölldorfer, F; Jakobs, K; Kleinknecht, K; Kröcker, M; Müller, A S; Nürnberger, H A; Quast, G; Renk, B; Rohne, E; Sander, H G; Schmeling, S; Wachsmuth, H W; Zeitnitz, C; Ziegler, T; Aubert, Jean-Jacques; Bonissent, A; Carr, J; Coyle, P; Ealet, A; Fouchez, D; Tilquin, A; Aleppo, M; Antonelli, M; Gilardoni, S S; Ragusa, F; Büscher, V; Dietl, H; Ganis, G; Hüttmann, K; Lütjens, G; Mannert, C; Männer, W; Moser, H G; Schael, S; Settles, Ronald; Seywerd, H C J; Stenzel, H; Wiedenmann, W; Wolf, G; Azzurri, P; Boucrot, J; Callot, O; Chen, S; Davier, M; Duflot, L; Grivaz, J F; Heusse, P; Jacholkowska, A; Lefrançois, J; Serin, L; Veillet, J J; Videau, I; De Vivie de Régie, J B; Zerwas, D; Bagliesi, G; Boccali, T; Bozzi, C; Calderini, G; Dell'Orso, R; Ferrante, I; Giassi, A; Gregorio, A; Ligabue, F; Marrocchesi, P S; Messineo, A; Palla, Fabrizio; Rizzo, G; Sanguinetti, G; Sguazzoni, G; Tenchini, Roberto; Venturi, A; Verdini, P G; Blair, G A; Coles, J; Cowan, G D; Green, M G; Hutchcroft, D E; Jones, L T; Medcalf, T; Strong, J A; Botterill, David R; Clifft, R W; Edgecock, T R; Norton, P R; Tomalin, I R; Bloch-Devaux, B; Colas, P; Fabbro, B; Faïf, G; Lançon, E; Lemaire, M C; Locci, E; Pérez, P; Rander, J; Renardy, J F; Rosowsky, A; Seager, P; Trabelsi, A; Tuchming, B; Vallage, B; Black, S N; Dann, J H; Loomis, C; Kim, H Y; Konstantinidis, N P; Litke, A M; McNeil, M A; Taylor, G; Booth, C N; Cartwright, S L; Combley, F; Hodgson, P N; Lehto, M H; Thompson, L F; Affholderbach, K; Böhrer, A; Brandt, S; Grupen, Claus; Hess, J; Misiejuk, A; Prange, G; Sieler, U; Borean, C; Giannini, G; Gobbo, B; Pütz, J; Rothberg, J E; Wasserbaech, S R; Williams, R W; Armstrong, S R; Elmer, P; Ferguson, D P S; Gao, Y; González, S; Hayes, O J; Hu, H; Jin, S; Kile, J; McNamara, P A; Nielsen, J; Orejudos, W; Pan, Y B; Saadi, Y; Scott, I J; Walsh, J; Von Wimmersperg-Töller, J H; Wu Sau Lan; Wu, X; Zobernig, G

2000-01-01

Bose-Einstein correlations are studied in semileptonicWW --> qqbarlnu and fully hadronic WW --> qqbarqqbar W-pair decays with the ALEPH detector at LEP at centre-of-mass energies of 172, 183 and 189GeV. They are compared with those made at the Z peak after correction for the different flavour compositions. A Monte Carlo model of Bose-Einsteincorrelations based on the JETSET hadronization scheme was tuned to the Z data and reproduces the correlations in the WW --> qqbarlnu events. The same Monte Carlo reproduces the correlations in the WW --> qqbarqqbarchannel assuming independent fragmentation of the two W's. A variant thismodel with Bose-Einstein correlations between decay products of different W's is disfavoured.

Exact solution of the one-dimensional Hubbard model with arbitrary boundary magnetic fields

Energy Technology Data Exchange (ETDEWEB)

Li, Yuan-Yuan; Cao, Junpeng [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Yang, Wen-Li [Institute of Modern Physics, Northwest University, Xian 710069 (China); Beijing Center for Mathematics and Information Interdisciplinary Sciences, Beijing, 100048 (China); Shi, Kangjie [Institute of Modern Physics, Northwest University, Xian 710069 (China); Wang, Yupeng, E-mail: yupeng@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China)

2014-02-15

The one-dimensional Hubbard model with arbitrary boundary magnetic fields is solved exactly via the Bethe ansatz methods. With the coordinate Bethe ansatz in the charge sector, the second eigenvalue problem associated with the spin sector is constructed. It is shown that the second eigenvalue problem can be transformed into that of the inhomogeneous XXX spin chain with arbitrary boundary fields which can be solved via the off-diagonal Bethe ansatz method.

A pure Hubbard model with demonstrable pairing adjacent to the Mott-insulating phase

International Nuclear Information System (INIS)

Champion, J D; Long, M W

2003-01-01

We introduce a Hubbard model on a particular class of geometries, and consider the effect of doping the highly spin-degenerate Mott-insulating state with a microscopic number of holes in the extreme strong-coupling limit. The geometry is quite general, with pairs of atomic sites at each superlattice vertex, and a highly frustrated inter-atomic connectivity: the one-dimensional realization is a chain of edge-sharing tetrahedra. The sole model parameter is the ratio of intra-pair to inter-pair hopping matrix elements. If the intra-pair hopping is negligible then introducing a microscopic number of holes results in a ferromagnetic Nagaoka groundstate. Conversely, if the intra-pair hopping is comparable with the inter-pair hopping then the groundstate is low spin with short-ranged spin correlations. We exactly solve the correlated motion of a pair of holes in such a state and find that, in 1d and 2d, they form a bound pair on a length scale that increases with diminishing binding energy. This result is pertinent to the long-standing problem of hole motion in the CuO 2 planes of the high-temperature superconductors: we have rigorously shown that, on our frustrated geometry, the holes pair up and a short-ranged low-spin state is generated by hole motion alone

Polaronic and bipolaronic structures in the adiabatic Hubbard-Holstein model involving 2 electrons and its extensions

International Nuclear Information System (INIS)

Proville, L.

1998-01-01

This thesis brings its contribution to the bipolaronic theory which might explain the origin of superconductivity at high temperature. A polaron is a quasiparticle made up of a localized electron and a deformation in the crystal structure. 2 electrons in singlet states localized on the same site form a bipolaron. Whenever the Coulomb repulsion between the 2 electrons is too strong bipolaron turns into 2 no bound polarons. We study the existence and the mobility of bipolarons. We describe the electron-phonon interaction by the Holstein term and the Coulomb repulsion by the Hubbard term. 2 assumptions are made: - the local electron-phonon interaction is strong and opposes the Coulomb repulsion between Hubbard type electrons - the system is close to the adiabatic limit. The system is reduced to 2 electrons in order to allow an exact treatment and the investigation of some bipolaronic bound states. At 2-dimensions the existence of bipolarons requires a very strong coupling which forbids any classical mobility. In some cases an important tunneling effect appears and we show that mobile bipolarons exist in a particular parameter range. Near the adiabatic limit we prove that polaronic and bipolaronic structures exist for a great number of electrons. (A.C.)

Branner-Hubbard Motions and attracting dynamics

DEFF Research Database (Denmark)

Petersen, Carsten Lunde; Tan, Lei

2006-01-01

We introduce a new notion of attracting dynamics, which is related to polynomial-like mappings. Also we review the Branner-Hubbard Motion and study its action on attracting dynamics.......We introduce a new notion of attracting dynamics, which is related to polynomial-like mappings. Also we review the Branner-Hubbard Motion and study its action on attracting dynamics....

Branner-Hubbard motions and attracting dynamics

DEFF Research Database (Denmark)

Petersen, Carsten Lunde; Tan, Lei

We introduce the new notion an aatracting dynamics, which is related to polynomial-likke mappings. Also we review the Branner-Hubbard motion and study its action on attracting dynamics.......We introduce the new notion an aatracting dynamics, which is related to polynomial-likke mappings. Also we review the Branner-Hubbard motion and study its action on attracting dynamics....

Breakdown of quasiparticle picture in the low-density limit of the 1D Hubbard model

International Nuclear Information System (INIS)

Qin Shaojin; Qian Tiezheng; Su Zhaobin

1995-03-01

Using the finite-size scaling of results obtained by exact diagonalization, we study the low-density limit of the one-dimensional Hubbard model. Calculating the quasiparticle weight, we demonstrate that for a given particle number N and system size L, there always exists a crossover point U c separating the Fermi-liquid (U c ) and non-Fermi-liquid (U > U c ) regimes (U is the Hubbard repulsion). We find that for a fixed N, U c is inversely proportional to L, keeping U c L/t constant (with t as the hopping integral), as L is large enough. It follows that in the low-density (in fact vanishing density) limit L → ∞, U c → 0, so the system is always in non-Fermi-liquid regime as long as U > 0. We show that our numerical results are consistent with the Bethe ansatz solution. (author). 11 refs, 3 figs

Solutions of the Two-Dimensional Hubbard Model: Benchmarks and Results from a Wide Range of Numerical Algorithms

Directory of Open Access Journals (Sweden)

2015-12-01

Full Text Available Numerical results for ground-state and excited-state properties (energies, double occupancies, and Matsubara-axis self-energies of the single-orbital Hubbard model on a two-dimensional square lattice are presented, in order to provide an assessment of our ability to compute accurate results in the thermodynamic limit. Many methods are employed, including auxiliary-field quantum Monte Carlo, bare and bold-line diagrammatic Monte Carlo, method of dual fermions, density matrix embedding theory, density matrix renormalization group, dynamical cluster approximation, diffusion Monte Carlo within a fixed-node approximation, unrestricted coupled cluster theory, and multireference projected Hartree-Fock methods. Comparison of results obtained by different methods allows for the identification of uncertainties and systematic errors. The importance of extrapolation to converged thermodynamic-limit values is emphasized. Cases where agreement between different methods is obtained establish benchmark results that may be useful in the validation of new approaches and the improvement of existing methods.

Nonperturbative Series Expansion of Green's Functions: The Anatomy of Resonant Inelastic X-Ray Scattering in the Doped Hubbard Model

Science.gov (United States)

Lu, Yi; Haverkort, Maurits W.

2017-12-01

We present a nonperturbative, divergence-free series expansion of Green's functions using effective operators. The method is especially suited for computing correlators of complex operators as a series of correlation functions of simpler forms. We apply the method to study low-energy excitations in resonant inelastic x-ray scattering (RIXS) in doped one- and two-dimensional single-band Hubbard models. The RIXS operator is expanded into polynomials of spin, density, and current operators weighted by fundamental x-ray spectral functions. These operators couple to different polarization channels resulting in simple selection rules. The incident photon energy dependent coefficients help to pinpoint main RIXS contributions from different degrees of freedom. We show in particular that, with parameters pertaining to cuprate superconductors, local spin excitation dominates the RIXS spectral weight over a wide doping range in the cross-polarization channel.

Bose-Einstein condensation in the relativistic ideal Bose gas.

Science.gov (United States)

Grether, M; de Llano, M; Baker, George A

2007-11-16

The Bose-Einstein condensation (BEC) critical temperature in a relativistic ideal Bose gas of identical bosons, with and without the antibosons expected to be pair-produced abundantly at sufficiently hot temperatures, is exactly calculated for all boson number densities, all boson point rest masses, and all temperatures. The Helmholtz free energy at the critical BEC temperature is lower with antibosons, thus implying that omitting antibosons always leads to the computation of a metastable state.

Bose-Einstein Condensation in the Relativistic Ideal Bose Gas

International Nuclear Information System (INIS)

Grether, M.; Llano, M. de; Baker, George A. Jr.

2007-01-01

The Bose-Einstein condensation (BEC) critical temperature in a relativistic ideal Bose gas of identical bosons, with and without the antibosons expected to be pair-produced abundantly at sufficiently hot temperatures, is exactly calculated for all boson number densities, all boson point rest masses, and all temperatures. The Helmholtz free energy at the critical BEC temperature is lower with antibosons, thus implying that omitting antibosons always leads to the computation of a metastable state

Bose-Einstein condensation of excitons in Cu2O

International Nuclear Information System (INIS)

Snoke, D.W.

1990-01-01

Free excitons provide the only experimental system other than helium in which the behavior of particles with mass is known to follow Bose-Einstein statistics. Experimental observations are presented of the kinetic energy distribution of excitons in the direct-gap semiconductor Cu 2 O, both the triplet orthoexciton state and the singlet paraexciton state. The density and temperature of the exciton gas closely follow the phase boundary for Bose-Einstein condensation. At the highest densities, the lower-lying paraexcitons take on an anomalous energy distribution with a sharp, high-energy edge. This odd distribution of particle energies may be associated with Bose-Einstein condensation into a state with nonzero momentum. Indeed, the excitons leave the region of their creation at supersonic velocities. In addition to the experimental observations, theoretical models are presented for several aspects of this nonequilibrium system. The equilibration of a nearly-ideal boson gas is modeled, finding that a significant time is required for the approach to condensation. The temperature and density of the excitons in steady state are modeled based on known classical kinetic effects in semiconductors, and the effects of Bose-Einstein statistics on these processes estimated

Coupling of Hubbard fermions with phonons in La{sub 2} CuO{sub 4}: A combined study using density-functional theory and the generalized tight-binding method

Energy Technology Data Exchange (ETDEWEB)

Shneyder, E.I., E-mail: shneyder@iph.krasn.ru [Kirensky Institute of Physics SB RAS, Krasnoyarsk 660036 (Russian Federation); Reshetnev Siberian State Aerospace University, Krasnoyarsk 660014 (Russian Federation); Spitaler, J. [Materials Center Leoben Forschung GmbH, Rosegger-Straße 18, A-8700 Leoben (Austria); Kokorina, E.E.; Nekrasov, I.A. [Institute of Electrophysics UB RAS, Amundsena Str. 106, 620016 Yekaterinburg (Russian Federation); Gavrichkov, V.A. [Kirensky Institute of Physics SB RAS, Krasnoyarsk 660036 (Russian Federation); Draxl, C. [Physics Department and IRIS Adlershof, Humboldt-Universität zu Berlin, Zum Großen Windkanal 6, 12489 Berlin (Germany); Ovchinnikov, S.G. [Kirensky Institute of Physics SB RAS, Krasnoyarsk 660036 (Russian Federation)

2015-11-05

We present results for the electron-phonon interaction of the Γ-point phonons in the tetragonal high-temperature phase of La{sub 2} CuO{sub 4} obtained from a hybrid scheme, combining density-functional theory (DFT) with the generalized tight-binding approach. As a starting point, eigenfrequencies and eigenvectors for the Γ-point phonons are determined from DFT within the frozen phonon approach utilizing the augmented plane wave + local orbitals method. The so obtained characteristics of electron-phonon coupling are converted into parameters of the generalized tight-binding method. This approach is a version of cluster perturbation theory and takes the strong on-site electron correlations into account. The obtained parameters describe the interaction of phonons with Hubbard fermions which form quasiparticle bands in strongly correlated electron systems. As a result, it is found that the Γ-point phonons with the strongest electron-phonon interaction are the A{sub 2u} modes (236 cm{sup −1}, 131 cm{sup −1} and 476 cm{sup −1}). Finally it is shown, that the single-electron spectral-weight redistribution between different Hubbard fermion quasiparticles results in a suppression of electron-phonon interaction which is strongest for the triplet Hubbard band with z oriented copper and oxygen electrons. - Highlights: • Electron-phonon interaction in strongly correlated electron systems is analyzed. • Interaction parameters between strongly correlated electrons and phonons are obtained. • The suppression of these parameters by strong electron correlations is demonstrated.

Spiral magnetism in the single-band Hubbard model: the Hartree-Fock and slave-boson approaches.

Science.gov (United States)

Igoshev, P A; Timirgazin, M A; Gilmutdinov, V F; Arzhnikov, A K; Irkhin, V Yu

2015-11-11

The ground-state magnetic phase diagram is investigated within the single-band Hubbard model for square and different cubic lattices. The results of employing the generalized non-correlated mean-field (Hartree-Fock) approximation and generalized slave-boson approach by Kotliar and Ruckenstein with correlation effects included are compared. We take into account commensurate ferromagnetic, antiferromagnetic, and incommensurate (spiral) magnetic phases, as well as phase separation into magnetic phases of different types, which was often lacking in previous investigations. It is found that the spiral states and especially ferromagnetism are generally strongly suppressed up to non-realistically large Hubbard U by the correlation effects if nesting is absent and van Hove singularities are well away from the paramagnetic phase Fermi level. The magnetic phase separation plays an important role in the formation of magnetic states, the corresponding phase regions being especially wide in the vicinity of half-filling. The details of non-collinear and collinear magnetic ordering for different cubic lattices are discussed.

Critical behavior near the Mott transition in the half-filled asymmetric Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Hoang, Anh-Tuan, E-mail: hatuan@iop.vast.ac.vn [Institute of Physics, Vietnam Academy of Science and Technology, Hanoi (Viet Nam); Le, Duc-Anh [Faculty of Physics, Hanoi National University of Education, Xuan Thuy 136, Cau Giay, Hanoi 10000 (Viet Nam)

2016-03-15

We study the half-filled asymmetric Hubbard model within the two-site dynamical mean field theory. At zero temperature, explicit expressions of the critical interaction U{sub c} for the Mott transition and the local self-energy are analytically derived. Critical behavior of the quasiparticle weights and the double occupancy are obtained analytically as functions of the on-site interaction U and the hopping asymmetry r. Our results are in good agreement with the ones obtained by much more sophisticated theory.

Generalized Hubbard Hamiltonian: renormalization group approach

International Nuclear Information System (INIS)

Cannas, S.A.; Tamarit, F.A.; Tsallis, C.

1991-01-01

We study a generalized Hubbard Hamiltonian which is closed within the framework of a Quantum Real Space Renormalization Group, which replaces the d-dimensional hypercubic lattice by a diamond-like lattice. The phase diagram of the generalized Hubbard Hamiltonian is analyzed for the half-filled band case in d = 2 and d = 3. Some evidence for superconductivity is presented. (author). 44 refs., 12 figs., 2 tabs

L Ron Hubbard's science fiction quest against psychiatry.

Science.gov (United States)

Hirshbein, Laura

2016-12-01

Layfayette Ronald Hubbard (1911-1986) was a colourful and prolific American writer of science fiction in the 1930s and 1940s. During the time between his two decades of productivity and his return to science fiction in 1980, Hubbard founded the Church of Scientology. In addition to its controversial status as a religion and its troubling pattern of intimidation and litigation directed towards its foes, Scientology is well known as an organised opponent to psychiatry. This paper looks at Hubbard's science fiction work to help understand the evolution of Scientology's antipsychiatry stance, as well as the alternative to psychiatry offered by Hubbard. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

Spin peierls instability against S-like anisotropic superconductivity in framework of the mean field RVB-Hubbard model

International Nuclear Information System (INIS)

Wrobel, P.; Jacak, L.

1988-01-01

It is shown theoretically that the superconducting transition in the framework of RVB mean field treatment in nearly half-filled band Hubbard model is substantially influenced by spin density wave instability. The reasonable SDW and SC ordering phase diagram for doped La 2 CuO 4 compounds is found

Rényi Entropies from Random Quenches in Atomic Hubbard and Spin Models

Science.gov (United States)

Elben, A.; Vermersch, B.; Dalmonte, M.; Cirac, J. I.; Zoller, P.

2018-02-01

We present a scheme for measuring Rényi entropies in generic atomic Hubbard and spin models using single copies of a quantum state and for partitions in arbitrary spatial dimensions. Our approach is based on the generation of random unitaries from random quenches, implemented using engineered time-dependent disorder potentials, and standard projective measurements, as realized by quantum gas microscopes. By analyzing the properties of the generated unitaries and the role of statistical errors, with respect to the size of the partition, we show that the protocol can be realized in existing quantum simulators and used to measure, for instance, area law scaling of entanglement in two-dimensional spin models or the entanglement growth in many-body localized systems.

Thermodynamics of two-parameter quantum group Bose and Fermi gases

International Nuclear Information System (INIS)

Algin, A.

2005-01-01

The high and low temperature thermodynamic properties of the two-parameter deformed quantum group Bose and Fermi gases with SU p/q (2) symmetry are studied. Starting with a SU p/q (2)-invariant bosonic as well as fermionic Hamiltonian, several thermodynamic functions of the system such as the average number of particles, internal energy and equation of state are derived. The effects of two real independent deformation parameters p and q on the properties of the systems are discussed. Particular emphasis is given to a discussion of the Bose-Einstein condensation phenomenon for the two-parameter deformed quantum group Bose gas. The results are also compared with earlier undeformed and one-parameter deformed versions of Bose and Fermi gas models. (author)

Breaking of SU(4) symmetry and interplay between strongly-correlated phases in the Hubbard model

Czech Academy of Sciences Publication Activity Database

Golubeva, A.; Sotnikov, A.; Cichy, A.; Kuneš, Jan; Hofstetter, W.

2017-01-01

Roč. 95, č. 12 (2017), s. 1-7, č. článku 125108. ISSN 2469-9950 EU Projects: European Commission(XE) 646807 - EXMAG Institutional support: RVO:68378271 Keywords : Hubbard model * SU(4) Subject RIV: BE - Theoretical Physics OBOR OECD: Atomic, molecular and chemical physics (physics of atoms and molecules including collision, interaction with radiation, magnetic resonances, Mössbauer effect) Impact factor: 3.836, year: 2016

Correlated density matrix theory of spatially inhomogeneous Bose fluids

International Nuclear Information System (INIS)

Gernoth, K.A.; Clark, J.W.; Ristig, M.L.

1994-06-01

In this paper, the variational Hartree-Jastrow theory of the ground state of spatially inhomogeneous Bose systems is extended to finite temperatures. The theory presented here is a generalization also in the sense that it extends the correlated density matrix approach, formulated previously for uniform Bose fluids, to systems with nonuniform density profiles. The method provides a framework in which the effects of thermal excitations on the spatial structure of a Bose fluid, as represented by the density profile and the two-body distribution functions, may be discussed on the basis on an ab initio microscopic description of the system. Thermal excitations make their appearance through self-consistently determined one-body and two-body potentials which enter the nonlinear, coupled Euler-Lagrange equations for the one-body density and for the pair distribution function. Since back-flow correlations are neglected, the excitations are described by a Feynman eigenvalue equation, suitably generalized to nonzero temperatures. The only external quantities entering the correlated density matrix theory elaborated here are the bare two-body interaction potential and, in actual applications, the boundary conditions to be imposed on the one-body density. 30 refs

Influence of trapping potentials on the phase diagram of bosonic atoms in optical lattices

International Nuclear Information System (INIS)

Giampaolo, S.M.; Illuminati, F.; Mazzarella, G.; De Siena, S.

2004-01-01

We study the effect of external trapping potentials on the phase diagram of bosonic atoms in optical lattices. We introduce a generalized Bose-Hubbard Hamiltonian that includes the structure of the energy levels of the trapping potential, and show that these levels are in general populated both at finite and zero temperature. We characterize the properties of the superfluid transition for this situation and compare them with those of the standard Bose-Hubbard description. We briefly discuss similar behaviors for fermionic systems

On Hubbard-Stratonovich transformations over hyperbolic domains

International Nuclear Information System (INIS)

Fyodorov, Yan V

2005-01-01

We discuss and prove the validity of the Hubbard-Stratonovich (HS) identities over hyperbolic domains which are used frequently in studies on disordered systems and random matrices. We also introduce a counterpart of the HS identity arising in disordered systems with 'chiral' symmetry. Apart from this we outline a way of deriving the nonlinear σ-model from the gauge-invariant Wegner k-orbital model avoiding the use of the HS transformations

Valence-bond theory of linear Hubbard and Pariser-Parr-Pople models

Science.gov (United States)

Soos, Z. G.; Ramasesha, S.

1984-05-01

The ground and low-lying states of finite quantum-cell models with one state per site are obtained exactly through a real-space basis of valence-bond (VB) diagrams that explicitly conserve the total spin. Regular and alternating Hubbard and Pariser-Parr-Pople (PPP) chains and rings with Ne electrons on N(PPP models, but differ from mean-field results. Molecular PPP parameters describe well the excitations of finite polyenes, odd polyene ions, linear cyanine dyes, and slightly overestimate the absorption peaks in polyacetylene (CH)x. Molecular correlations contrast sharply with uncorrelated descriptions of topological solitons, which are modeled by regular polyene radicals and their ions for both wide and narrow alternation crossovers. Neutral solitons have no midgap absorption and negative spin densities, while the intensity of the in-gap excitation of charged solitons is not enhanced. The properties of correlated states in quantum-cell models with one valence state per site are discussed in the adiabatic limit for excited-state geometries and instabilities to dimerization.

Mott-Hubbard transition and Anderson localization: A generalized dynamical mean-field theory approach

International Nuclear Information System (INIS)

Kuchinskii, E. Z.; Nekrasov, I. A.; Sadovskii, M. V.

2008-01-01

The DOS, the dynamic (optical) conductivity, and the phase diagram of a strongly correlated and strongly disordered paramagnetic Anderson-Hubbard model are analyzed within the generalized dynamical mean field theory (DMFT + Σ approximation). Strong correlations are taken into account by the DMFT, and disorder is taken into account via an appropriate generalization of the self-consistent theory of localization. The DMFT effective single-impurity problem is solved by a numerical renormalization group (NRG); we consider the three-dimensional system with a semielliptic DOS. The correlated metal, Mott insulator, and correlated Anderson insulator phases are identified via the evolution of the DOS and dynamic conductivity, demonstrating both the Mott-Hubbard and Anderson metal-insulator transition and allowing the construction of the complete zero-temperature phase diagram of the Anderson-Hubbard model. Rather unusual is the possibility of a disorder-induced Mott insulator-to-metal transition

Universal Themes of Bose-Einstein Condensation

Science.gov (United States)

Proukakis, Nick P.; Snoke, David W.; Littlewood, Peter B.

2017-04-01

Foreword; List of contributors; Preface; Part I. Introduction: 1. Universality and Bose-Einstein condensation: perspectives on recent work D. W. Snoke, N. P. Proukakis, T. Giamarchi and P. B. Littlewood; 2. A history of Bose-Einstein condensation of atomic hydrogen T. Greytak and D. Kleppner; 3. Twenty years of atomic quantum gases: 1995-2015 W. Ketterle; 4. Introduction to polariton condensation P. B. Littlewood and A. Edelman; Part II. General Topics: Editorial notes; 5. The question of spontaneous symmetry breaking in condensates D. W. Snoke and A. J. Daley; 6. Effects of interactions on Bose-Einstein condensation R. P. Smith; 7. Formation of Bose-Einstein condensates M. J. Davis, T. M. Wright, T. Gasenzer, S. A. Gardiner and N. P. Proukakis; 8. Quenches, relaxation and pre-thermalization in an isolated quantum system T. Langen and J. Schmiedmayer; 9. Ultracold gases with intrinsic scale invariance C. Chin; 10. Berezinskii-Kosterlitz-Thouless phase of a driven-dissipative condensate N. Y. Kim, W. H. Nitsche and Y. Yamamoto; 11. Superfluidity and phase correlations of driven dissipative condensates J. Keeling, L. M. Sieberer, E. Altman, L. Chen, S. Diehl and J. Toner; 12. BEC to BCS crossover from superconductors to polaritons A. Edelman and P. B. Littlewood; Part III. Condensates in Atomic Physics: Editorial notes; 13. Probing and controlling strongly correlated quantum many-body systems using ultracold quantum gases I. Bloch; 14. Preparing and probing chern bands with cold atoms N. Goldman, N. R. Cooper and J. Dalibard; 15. Bose-Einstein condensates in artificial gauge fields L. J. LeBlanc and I. B. Spielman; 16. Second sound in ultracold atomic gases L. Pitaevskii and S. Stringari; 17. Quantum turbulence in atomic Bose-Einstein condensates N. G. Parker, A. J. Allen, C. F. Barenghi and N. P. Proukakis; 18. Spinor-dipolar aspects of Bose-Einstein condensation M. Ueda; Part IV. Condensates in Condensed Matter Physics: Editorial notes; 19. Bose

Theory of a Nearly Two-Dimensional Dipolar Bose Gas

Science.gov (United States)

2016-05-11

order to be published, he sent the paper to Einstein to translate it. The other contributing scientist is world famous physicist Albert Einstein , maybe...mechanical state, a Bose- Einstein condensate (BEC), where the atoms cease to behave like distinguishable entities, and instead form a single macroscopic...model in both three- and two-dimensional geometries. 15. SUBJECT TERMS Bose Einstein condensation, ultracold physics, condensed matter, dipoles 16

Antiferromagnetic order in the Hubbard model on the Penrose lattice

Science.gov (United States)

Koga, Akihisa; Tsunetsugu, Hirokazu

2017-12-01

We study an antiferromagnetic order in the ground state of the half-filled Hubbard model on the Penrose lattice and investigate the effects of quasiperiodic lattice structure. In the limit of infinitesimal Coulomb repulsion U →+0 , the staggered magnetizations persist to be finite, and their values are determined by confined states, which are strictly localized with thermodynamics degeneracy. The magnetizations exhibit an exotic spatial pattern, and have the same sign in each of cluster regions, the size of which ranges from 31 sites to infinity. With increasing U , they continuously evolve to those of the corresponding spin model in the U =∞ limit. In both limits of U , local magnetizations exhibit a fairly intricate spatial pattern that reflects the quasiperiodic structure, but the pattern differs between the two limits. We have analyzed this pattern change by a mode analysis by the singular value decomposition method for the fractal-like magnetization pattern projected into the perpendicular space.

Pre-relaxation in weakly interacting models

Science.gov (United States)

Bertini, Bruno; Fagotti, Maurizio

2015-07-01

We consider time evolution in models close to integrable points with hidden symmetries that generate infinitely many local conservation laws that do not commute with one another. The system is expected to (locally) relax to a thermal ensemble if integrability is broken, or to a so-called generalised Gibbs ensemble if unbroken. In some circumstances expectation values exhibit quasi-stationary behaviour long before their typical relaxation time. For integrability-breaking perturbations, these are also called pre-thermalisation plateaux, and emerge e.g. in the strong coupling limit of the Bose-Hubbard model. As a result of the hidden symmetries, quasi-stationarity appears also in integrable models, for example in the Ising limit of the XXZ model. We investigate a weak coupling limit, identify a time window in which the effects of the perturbations become significant and solve the time evolution through a mean-field mapping. As an explicit example we study the XYZ spin-\\frac{1}{2} chain with additional perturbations that break integrability. One of the most intriguing results of the analysis is the appearance of persistent oscillatory behaviour. To unravel its origin, we study in detail a toy model: the transverse-field Ising chain with an additional nonlocal interaction proportional to the square of the transverse spin per unit length (2013 Phys. Rev. Lett. 111 197203). Despite being nonlocal, this belongs to a class of models that emerge as intermediate steps of the mean-field mapping and shares many dynamical properties with the weakly interacting models under consideration.

Dark-dark-soliton dynamics in two density-coupled Bose-Einstein condensates

Science.gov (United States)

Morera, I.; Mateo, A. Muñoz; Polls, A.; Juliá-Díaz, B.

2018-04-01

We study the one-dimensional dynamics of dark-dark solitons in the miscible regime of two density-coupled Bose-Einstein condensates having repulsive interparticle interactions within each condensate (g >0 ). By using an adiabatic perturbation theory in the parameter g12/g , we show that, contrary to the case of two solitons in scalar condensates, the interactions between solitons are attractive when the interparticle interactions between condensates are repulsive g12>0 . As a result, the relative motion of dark solitons with equal chemical potential μ is well approximated by harmonic oscillations of angular frequency wr=(μ /ℏ ) √{(8 /15 ) g12/g } . We also show that, in finite systems, the resonance of this anomalous excitation mode with the spin-density mode of lowest energy gives rise to alternating dynamical instability and stability fringes as a function of the perturbative parameter. In the presence of harmonic trapping (with angular frequency Ω ) the solitons are driven by the superposition of two harmonic motions at a frequency given by w2=(Ω/√{2 }) 2+wr2 . When g12<0 , these two oscillators compete to give rise to an overall effective potential that can be either single well or double well through a pitchfork bifurcation. All our theoretical results are compared with numerical solutions of the Gross-Pitaevskii equation for the dynamics and the Bogoliubov equations for the linear stability. A good agreement is found between them.

Coherent oscillations between two weakly coupled Bose-Einstein condensates: Josephson effects, π oscillations, and macroscopic quantum self-trapping

International Nuclear Information System (INIS)

Raghavan, S.; Smerzi, A.; Fantoni, S.; Shenoy, S.R.

2001-03-01

We discuss the coherent atomic oscillations between two weakly coupled Bose-Einstein condensates. The weak link is provided by a laser barrier in a (possibly asymmetric) double-well trap or by Raman coupling between two condensates in different hyperfine levels. The boson Josephson junction (BJJ) dynamics is described by the two-mode nonlinear Gross-Pitaevskii equation that is solved analytically in terms of elliptic functions. The BJJ, being a neutral, isolated system, allows the investigations of dynamical regimes for the phase difference across the junction and for the population imbalance that are not accessible with superconductor Josephson junctions (SJJ's). These include oscillations with either or both of the following properties: (i) the time-averaged value of the phase is equal to π (π-phase oscillations); (ii) the average population imbalance is nonzero, in states with macroscopic quantum self-trapping. The (nonsinusoidal) generalization of the SJJ ac and plasma oscillations and the Shapiro resonance can also be observed. We predict the collapse of experimental data (corresponding to different trap geometries and the total number of condensate atoms) onto a single universal curve for the inverse period of oscillations. Analogies with Josephson oscillations between two weakly coupled reservoirs of 3 He-B and the internal Josephson effect in 3 He-A are also discussed. (author)

Penson-Kolb-Hubbard model: A study of the competition between single-particle and pair hopping in one dimension

International Nuclear Information System (INIS)

Hui, A.; Doniach, S.

1993-01-01

In this paper, we present a study of the ground-state phase diagram of a one-dimensional quantum chain, the Penson-Kolb-Hubbard model, H=-summation i ,η=±1,σ (tc i+ησ † c iσ +Vc i+η↑ † c i+η↓ † c i↓ ci↑)+ summation i Un i↑ ni↓ at half filling. We have examined the system using exact diagonalization for samples of up to 12 sites and employed two techniques, eigenprojection decomposition and twisted-boundary conditions, in analyzing the data. These techniques allow us to characterize the ground state in a manner insensitive to changes in sample size and provide us with a clean way to visualize the physics. When used with the ''correct'' order parameter, qualitative features emerge even for sample sizes as small as six sites. We find that the second-order charge-density-wave--spin-density-wave transition in the weak-coupling limit (t much-gt U∼2V) turns into a first-order superconducting--antiferromagnetic transition in the strong-coupling regime [t much-lt U∼(4/π)V]. We also observe evidence of a charge-density-wave--superconducting transition in the parameter range (t∼V much-gt U). These three transition lines meet together at a tricritical point at (t:U:V)∼(0.04:0.54:0.42). A naive renormalization-group analysis in the intermediate-coupling regime produces results consistent with this conclusion

Magnetic excitation spectra of strongly correlated quasi-one-dimensional systems: Heisenberg versus Hubbard-like behavior

Science.gov (United States)

Nocera, A.; Patel, N. D.; Fernandez-Baca, J.; Dagotto, E.; Alvarez, G.

2016-11-01

We study the effects of charge degrees of freedom on the spin excitation dynamics in quasi-one-dimensional magnetic materials. Using the density matrix renormalization group method, we calculate the dynamical spin structure factor of the Hubbard model at half electronic filling on a chain and on a ladder geometry, and compare the results with those obtained using the Heisenberg model, where charge degrees of freedom are considered frozen. For both chains and two-leg ladders, we find that the Hubbard model spectrum qualitatively resembles the Heisenberg spectrum—with low-energy peaks resembling spinonic excitations—already at intermediate on-site repulsion as small as U /t ˜2 -3 , although ratios of peak intensities at different momenta continue evolving with increasing U /t converging only slowly to the Heisenberg limit. We discuss the implications of these results for neutron scattering experiments and we propose criteria to establish the values of U /t of quasi-one-dimensional systems described by one-orbital Hubbard models from experimental information.

Quantum critical behavior in three-dimensional one-band Hubbard model at half-filling

International Nuclear Information System (INIS)

Karchev, Naoum

2013-01-01

A one-band Hubbard model with hopping parameter t and Coulomb repulsion U is considered at half-filling. By means of the Schwinger bosons and slave fermions representation of the electron operators and integrating out the spin–singlet Fermi fields an effective Heisenberg model with antiferromagnetic exchange constant is obtained for vectors which identifies the local orientation of the spin of the itinerant electrons. The amplitude of the spin vectors is an effective spin of the itinerant electrons accounting for the fact that some sites, in the ground state, are doubly occupied or empty. Accounting adequately for the magnon–magnon interaction the Néel temperature is calculated. When the ratio t/U is small enough (t/U ≤0.09) the effective model describes a system of localized electrons. Increasing the ratio increases the density of doubly occupied states which in turn decreases the effective spin and Néel temperature. The phase diagram in the plane of temperature (T N )/U and parameter t/U is presented. The quantum critical point (T N =0) is reached at t/U =0.9. The magnons in the paramagnetic phase are studied and the contribution of the magnons’ fluctuations to the heat capacity is calculated. At the Néel temperature the heat capacity has a peak which is suppressed when the system approaches a quantum critical point. It is important to stress that, at half-filling, the ground state, determined by fermions, is antiferromagnetic. The magnon fluctuations drive the system to quantum criticality and when the effective spin is critically small these fluctuations suppress the magnetic order. -- Highlights: •Technique of calculation is introduced which permits us to study the magnons’ fluctuations. •Quantum critical point is obtained in the one-band 3D Hubbard model at half-filling. •The present analytical results supplement the numerical ones (see Fig. 7)

Bose condensation in (random traps

Directory of Open Access Journals (Sweden)

V.A. Zagrebnov

2009-01-01

Full Text Available We study a non-interacting (perfect Bose-gas in random external potentials (traps. It is shown that a generalized Bose-Einstein condensation in the random eigenstates manifests if and only if the same occurs in the one-particle kinetic-energy eigenstates, which corresponds to the generalized condensation of the free Bose-gas. Moreover, we prove that the amounts of both condensate densities are equal. This statement is relevant for justification of the Bogoliubov approximation} in the theory of disordered boson systems.

Exact many-electron ground states on diamond and triangle Hubbard chains

International Nuclear Information System (INIS)

Gulacsi, Zsolt; Kampf, Arno; Vollhardt, Dieter

2009-01-01

We construct exact ground states of interacting electrons on triangle and diamond Hubbard chains. The construction requires (1) a rewriting of the Hamiltonian into positive semidefinite form, (2) the construction of a many-electron ground state of this Hamiltonian, and (3) the proof of the uniqueness of the ground state. This approach works in any dimension, requires no integrability of the model, and only demands sufficiently many microscopic parameters in the Hamiltonian which have to fulfill certain relations. The scheme is first employed to construct exact ground state for the diamond Hubbard chain in a magnetic field. These ground states are found to exhibit a wide range of properties such as flat-band ferromagnetism and correlation induced metallic, half-metallic or insulating behavior, which can be tuned by changing the magnetic flux, local potentials, or electron density. Detailed proofs of the uniqueness of the ground states are presented. By the same technique exact ground states are constructed for triangle Hubbard chains and a one-dimensional periodic Anderson model with nearest-neighbor hybridization. They permit direct comparison with results obtained by variational techniques for f-electron ferromagnetism due to a flat band in CeRh 3 B 2 . (author)

Hubbard interaction in the arbitrary Chern number insulator: A mean-field study

Energy Technology Data Exchange (ETDEWEB)

Wang, Yi-Xiang, E-mail: wangyixiang@jiangnan.edu.cn [School of Science, Jiangnan University, Wuxi 214122 (China); Cao, Jie [College of Science, Hohai University, Nanjing 210098 (China)

2017-05-10

The low-dimensional electron gas owing topological property has attracted many interests recently. In this work, we study the influence of the electron-electron interaction on the arbitrary Chern number insulator. Using the mean-field method, we approximately solve the Hubbard model in the half-filling case and obtain the phase diagrams in different parametric spaces. We further verify the results by calculating the entanglement spectrum, which contains C chiral modes and corresponds to a real space partitioning. - Highlights: • In this work, we made a mean-field study of the Hubbard interaction in the arbitrary Chern number insulator. • We point out that how the Zeeman splitting, the local magnetization and the Hubbard interaction are intimately related. • The mean-field phase diagrams are obtained in different parametric spaces. • The Chern number phase is demonstrated by calculating the entanglement spectrum.

Collision of bright vector solitons in two-component Bose-Einstein condensates

International Nuclear Information System (INIS)

Ramesh Kumar, V.; Radha, R.; Wadati, Miki

2010-01-01

We investigate the coupled Gross-Pitaevskii equation describing the dynamics of two hyperfine states of Bose-Einstein condensates and deduce the integrability condition for the propagation of bright vector solitons. We show how the transient trap and scattering length can be suitably tailored to bring about fascinating collisional dynamics of vector solitons.

The two-hole ground state of the Hubbard-Anderson model, approximated by a variational RVB-type wave function

NARCIS (Netherlands)

Traa, M.R.M.J.; Traa, M.R.M.J.; Caspers, W.J.; Caspers, W.J.; Banning, E.J.; Banning, E.J.

1994-01-01

In this paper the Hubbard-Anderson model on a square lattice with two holes is studied. The ground state (GS) is approximated by a variational RVB-type wave function. The holes interact by exchange of a localized spin excitation (SE), which is created or absorbed if a hole moves to a

Coherence and entanglement in the ground state of a bosonic Josephson junction: From macroscopic Schroedinger cat states to separable Fock states

International Nuclear Information System (INIS)

Mazzarella, G.; Toigo, F.; Salasnich, L.; Parola, A.

2011-01-01

We consider a bosonic Josephson junction made of N ultracold and dilute atoms confined by a quasi-one-dimensional double-well potential within the two-site Bose-Hubbard model framework. The behavior of the system is investigated at zero temperature by varying the interatomic interaction from the strongly attractive regime to the repulsive one. We show that the ground state exhibits a crossover from a macroscopic Schroedinger-cat state to a separable Fock state through an atomic coherent regime. By diagonalizing the Bose-Hubbard Hamiltonian we characterize the emergence of the macroscopic cat states by calculating the Fisher information F, the coherence by means of the visibility α of the interference fringes in the momentum distribution, and the quantum correlations by using the entanglement entropy S. Both Fisher information and visibility are shown to be related to the ground-state energy by employing the Hellmann-Feynman theorem. This result, together with a perturbative calculation of the ground-state energy, allows simple analytical formulas for F and α to be obtained over a range of interactions, in excellent agreement with the exact diagonalization of the Bose-Hubbard Hamiltonian. In the attractive regime the entanglement entropy attains values very close to its upper limit for a specific interaction strength lying in the region where coherence is lost and self-trapping sets in.

Ising tricriticality in the extended Hubbard model with bond dimerization

Science.gov (United States)

Fehske, Holger; Ejima, Satoshi; Lange, Florian; Essler, Fabian H. L.

We explore the quantum phase transition between Peierls and charge-density-wave insulating states in the one-dimensional, half-filled, extended Hubbard model with explicit bond dimerization. We show that the critical line of the continuous Ising transition terminates at a tricritical point, belonging to the universality class of the tricritical Ising model with central charge c=7/10. Above this point, the quantum phase transition becomes first order. Employing a numerical matrix-product-state based (infinite) density-matrix renormalization group method we determine the ground-state phase diagram, the spin and two-particle charge excitations gaps, and the entanglement properties of the model with high precision. Performing a bosonization analysis we can derive a field description of the transition region in terms of a triple sine-Gordon model. This allows us to derive field theory predictions for the power-law (exponential) decay of the density-density (spin-spin) and bond-order-wave correlation functions, which are found to be in excellent agreement with our numerical results. This work was supported by Deutsche Forschungsgemeinschaft (Germany), SFB 652, project B5, and by the EPSRC under Grant No. EP/N01930X/1 (FHLE).

Phase separation of superconducting phases in the Penson–Kolb–Hubbard model

International Nuclear Information System (INIS)

Kapcia, Konrad Jerzy; Czart, Wojciech Robert; Ptok, Andrzej

2016-01-01

In this paper, we determine the phase diagrams (for T = 0 as well as T > 0) of the Penson–Kolb–Hubbard model for two dimensional square lattice within Hartree–Fock mean-field theory focusing on an investigation of superconducting phases and on a possibility of the occurrence of the phase separation. We obtain that the phase separation, which is a state of coexistence of two different superconducting phases (with s- and η-wave symmetries), occurs in definite ranges of the electron concentration. In addition, increasing temperature can change the symmetry of the superconducting order parameter (from η-wave into s-wave). The system considered exhibits also an interesting multicritical behaviour including bicritical points. The relevance of the results to experiments for real materials is also discussed. (author)

Phase Separation of Superconducting Phases in the Penson-Kolb-Hubbard Model

Science.gov (United States)

Jerzy Kapcia, Konrad; Czart, Wojciech Robert; Ptok, Andrzej

2016-04-01

In this paper, we determine the phase diagrams (for T = 0 as well as T > 0) of the Penson-Kolb-Hubbard model for two dimensional square lattice within Hartree-Fock mean-field theory focusing on an investigation of superconducting phases and on a possibility of the occurrence of the phase separation. We obtain that the phase separation, which is a state of coexistence of two different superconducting phases (with s- and η-wave symmetries), occurs in definite ranges of the electron concentration. In addition, increasing temperature can change the symmetry of the superconducting order parameter (from η-wave into s-wave). The system considered exhibits also an interesting multicritical behaviour including bicritical points. The relevance of the results to experiments for real materials is also discussed.

Kinetic theory of collective excitations and damping in Bose-Einstein condensed gases

NARCIS (Netherlands)

Al Khawaja, U.; Stoof, H.T.C.

2000-01-01

We calculate the frequencies and damping rates of the low-lying collective modes of a Bose-Einstein condensed gas at nonzero temperature. We use a complex nonlinear Schrödinger equation to determine the dynamics of the condensate atoms, and couple it to a Boltzmann equation for the noncondensate

Excitations of Bose-Einstein condensates at finite temperatures

International Nuclear Information System (INIS)

Rusch, M.

2000-01-01

Recent experimental observations of collective excitations of Bose condensed atomic vapours have stimulated interest in the microscopic description of the dynamics of a Bose-Einstein condensate confined in an external potential. We present a finite temperature field theory for collective excitations of trapped Bose-Einstein condensates and use a finite-temperature linear response formalism, which goes beyond the simple mean-field approximation of the Gross-Pitaevskii equation. The effect of the non-condensed thermal atoms we include using perturbation theory in a quasiparticle basis. This presents a simple scheme to understand the interaction between condensate and non-condensed atoms and enables us to include the effect the condensate has on collision dynamics. At first we limit our treatment to the case of a spatially homogeneous Bose gas. We include the effect of pair and triplet anomalous averages and thus obtain a gapless theory for the excitations of a weakly interacting system, which we can link to well known results for Landau and Beliaev damping rates. A gapless theory for trapped systems with a static thermal component follows straightforwardly. We then investigate finite temperature excitations of a condensate in a spherically symmetric harmonic trap. We avoid approximations to the density of states and thus emphasise finite size aspects of the problem. We show that excitations couple strongly to a restricted number of modes, giving rise to resonance structure in their frequency spectra. Where possible we derive energy shifts and lifetimes of excitations. For one particular mode, the breathing mode, the effects of the discreteness of the system are sufficiently pronounced that the simple picture of an energy shift and width fails. Experiments in spherical traps have recently become feasible and should be able to test our detailed quantitative predictions. (author)

Satyendranath Bose: Co-Founder of Quantum Statistics

Science.gov (United States)

Blanpied, William A.

1972-01-01

Satyendranath Bose was first to prove Planck's Law by using ideal quantum gas. Einstein credited Bose for this first step in the development of quantum statistical mechanics. Bose did not realize the importance of his work, perhaps because of peculiar academic settings in India under British rule. (PS)

Des proprietes de l'etat normal du modele de Hubbard bidimensionnel

Science.gov (United States)

Lemay, Francois

Depuis leur decouverte, les etudes experimentales ont demontre que les supra-conducteurs a haute temperature ont une phase normale tres etrange. Les proprietes de ces materiaux ne sont pas bien decrites par la theorie du liquide de Fermi. Le modele de Hubbard bidimensionnel, bien qu'il ne soit pas encore resolu, est toujours considere comme un candidat pour expliquer la physique de ces composes. Dans cet ouvrage, nous mettons en evidence plusieurs proprietes electroniques du modele qui sont incompatibles avec l'existence de quasi-particules. Nous montrons notamment que la susceptibilite des electrons libres sur reseau contient des singularites logarithmiques qui influencent de facon determinante les proprietes de la self-energie a basse frequence. Ces singularites sont responsables de la destruction des quasi-particules. En l'absence de fluctuations antiferromagnetiques, elles sont aussi responsables de l'existence d'un petit pseudogap dans le poids spectral au niveau de Fermi. Les proprietes du modele sont egalement etudiees pour une surface de Fermi similaire a celle des supraconducteurs a haute temperature. Un parallele est etabli entre certaines caracteristiques du modele et celles de ces materiaux.

Second order approximation for optical polaron in the strong coupling case

International Nuclear Information System (INIS)

Bogolubov, N.N. Jr.

1993-11-01

Here we propose a method of construction second order approximation for ground state energy for class of model Hamiltonian with linear type interaction on Bose operators in strong coupling case. For the application of the above method we have considered polaron model and propose construction set of nonlinear differential equations for definition ground state energy in strong coupling case. We have considered also radial symmetry case. (author). 10 refs

Selfenergy effect on the magnetic ordering transition in the mono- and bilayer honeycomb Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Honerkamp, Carsten [Institute for Theoretical Solid State Physics, RWTH Aachen University (Germany); JARA - Fundamentals of Future Information Technology, Aachen (Germany)

2017-11-15

We investigate the impact of electron self-energy corrections on potential antiferromagnetic ordering instabilities in mono- and bilayer graphene, modeled by a Hubbard-type lattice model with onsite interactions among the electrons, using a self-consistent random phase approximation (RPA). In qualitative agreement with earlier studies we find that the electronic interactions cause non-Fermi liquid behavior at low energies. In self-consistent RPA, the transition scales for antiferromagnetic ordering are renormalized significantly by these self-energy effects, both for interaction-driven and temperature-driven cases. (copyright 2017 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

About long range pairing correlations in the Hubbard U-t-t' models

International Nuclear Information System (INIS)

Moreo, A.

1991-01-01

Using a quantum Monte Carlo method the authors measured pair correlation functions with different symmetries as a function of the filling, U/t and t'/t for the Hubbard and U-t-t' models. For the first time the Monte Carlo results are presented for U/t larger than the bandwidth 8t, away from half-filling. D-wave and extended S-wave pairing correlations are enhanced. D-wave pairing is stronger at half-filling but this behavior is reversed when the filling decreases. However, none of the eight pairing correlations that were studied increases as a function of lattice size, which makes the existence of long range superconducting order unlikely. (author). 10 refs.; 5 figs

The onset of chaotic symbolic synchronization between population inversions in an array of weakly-coupled Bose-Einstein condensates

International Nuclear Information System (INIS)

Pando L, C.L.; Doedel, E.J.

2004-07-01

We investigate the onset of chaotic dynamics of the one-dimensional discrete nonlinear Schroedinger equation (DNLSE) with periodic boundary conditions in the presence of a single on-site defect. This model describes a ring of weakly- coupled Bose-Einstein condensates. We focus on the transition to global stochasticity in three different scenarios as the defect is changed. We make use of a suitable Poincare section and continuation methods. Numerical continuation enables us to find different families of stationary solutions, where certain bifurcations lead to global stochasticity. The global stochasticity is characterized by chaotic symbolic synchronization between the population inversions of certain pairs of condensates. We have seen that the Poincare cycles are useful to gain insight in the dynamics of this problem. Indeed, the return maps of the Poincare cycles have been used successfully to follow the motion along the stochastic layers of different resonances in the chaotic self-trapping regime. Moreover, the time series of the Poincare cycles suggests that in the global stochasticity regime the dynamics is, to some extent, Markovian, in spite of the fact that the condensates are phase locked with almost the same phase. This phase locking induces a peculiar local interference of the matter waves of the condensates. (author)

Luttinger and Hubbard sum rules: are they compatible?

International Nuclear Information System (INIS)

Matho, K.

1992-01-01

A so-called Hubbard sum rule determines the weight of a satellite in fermionic single-particle excitations with strong local repulsion (U→∞). Together with the Luttinger sum rule, this imposes two different energy scales on the remaining finite excitations. In the Hubbard chain, this has been identified microscopically as being due to a separation of spin and charge. (orig.)

Emergent low-energy bound states in the two-orbital Hubbard model

Science.gov (United States)

Núñez-Fernández, Y.; Kotliar, G.; Hallberg, K.

2018-03-01

A repulsive Coulomb interaction between electrons in different orbitals in correlated materials can give rise to bound quasiparticle states. We study the nonhybridized two-orbital Hubbard model with intra- (inter)orbital interaction U (U12) and different bandwidths using an improved dynamical mean-field theory numerical technique which leads to reliable spectra on the real energy axis directly at zero temperature. We find that a finite density of states at the Fermi energy in one band is correlated with the emergence of well-defined quasiparticle states at excited energies Δ =U -U12 in the other band. These excitations are interband holon-doublon bound states. At the symmetric point U =U12 , the quasiparticle peaks are located at the Fermi energy, leading to a simultaneous and continuous Mott transition settling a long-standing controversy.

Interplay of Anderson localization and strong interaction in disordered systems

Energy Technology Data Exchange (ETDEWEB)

Henseler, Peter

2010-01-15

We study the interplay of disorder localization and strong local interactions within the Anderson-Hubbard model. Taking into account local Mott-Hubbard physics and static screening of the disorder potential, the system is mapped onto an effective single-particle Anderson model, which is studied within the self-consistent theory of electron localization. For fermions, we find rich nonmonotonic behavior of the localization length {xi}, particularly in two-dimensional systems, including an interaction-induced exponential enhancement of {xi} for small and intermediate disorders and a strong reduction of {xi} due to hopping suppression by strong interactions. In three dimensions, we identify for half filling a Mott-Hubbard-assisted Anderson localized phase existing between the metallic and the Mott-Hubbard-gapped phases. For small U there is re-entrant behavior from the Anderson localized phase to the metallic phase. For bosons, the unrestricted particle occupation number per lattice site yields a monotonic enhancement of {xi} as a function of decreasing interaction, which we assume to persist until the superfluid Bose-Einstein condensate phase is entered. Besides, we study cold atomic gases expanding, by a diffusion process, in a weak random potential. We show that the density-density correlation function of the expanding gas is strongly affected by disorder and we estimate the typical size of a speckle spot, i.e., a region of enhanced or depleted density. Both a Fermi gas and a Bose-Einstein condensate (in a mean-field approach) are considered. (orig.)

Interplay of Anderson localization and strong interaction in disordered systems

International Nuclear Information System (INIS)

Henseler, Peter

2010-01-01

We study the interplay of disorder localization and strong local interactions within the Anderson-Hubbard model. Taking into account local Mott-Hubbard physics and static screening of the disorder potential, the system is mapped onto an effective single-particle Anderson model, which is studied within the self-consistent theory of electron localization. For fermions, we find rich nonmonotonic behavior of the localization length ξ, particularly in two-dimensional systems, including an interaction-induced exponential enhancement of ξ for small and intermediate disorders and a strong reduction of ξ due to hopping suppression by strong interactions. In three dimensions, we identify for half filling a Mott-Hubbard-assisted Anderson localized phase existing between the metallic and the Mott-Hubbard-gapped phases. For small U there is re-entrant behavior from the Anderson localized phase to the metallic phase. For bosons, the unrestricted particle occupation number per lattice site yields a monotonic enhancement of ξ as a function of decreasing interaction, which we assume to persist until the superfluid Bose-Einstein condensate phase is entered. Besides, we study cold atomic gases expanding, by a diffusion process, in a weak random potential. We show that the density-density correlation function of the expanding gas is strongly affected by disorder and we estimate the typical size of a speckle spot, i.e., a region of enhanced or depleted density. Both a Fermi gas and a Bose-Einstein condensate (in a mean-field approach) are considered. (orig.)

Condensation of bosons with Rashba-Dresselhaus spin-orbit coupling

International Nuclear Information System (INIS)

Baym, Gordon; Ozawa, Tomoki

2014-01-01

Cold atomic Bose-Einstein systems in the presence of simulated Rashba- Dresselhaus spin-orbit coupling exhibit novel physical features. With pure in-plane Rashba coupling the system is predicted in Bogoliubov-Hartree-Fock to have a stable Bose condensate below a critical temperature, even though the effective density of states is two-dimensional. In addition the system has a normal state at all temperatures. We review here the new physics when the system has such spin-orbit coupling, and discuss the nature of the finite temperature condensation phase transition from the normal to condensed phases.

Hubbard physics in the PAW GW approximation

Energy Technology Data Exchange (ETDEWEB)

Booth, J. M., E-mail: jamie.booth@rmit.edu.au; Smith, J. S.; Russo, S. P. [Theoretical Chemical and Quantum Physics, School of Science, RMIT University, Melbourne, VIC (Australia); Drumm, D. W. [Theoretical Chemical and Quantum Physics, School of Science, RMIT University, Melbourne, VIC (Australia); Australian Research Council Centre of Excellence for Nanoscale BioPhotonics, School of Science, RMIT University, Melbourne, VIC (Australia); Casey, P. S. [CSIRO Manufacturing, Clayton, VIC (Australia)

2016-06-28

It is demonstrated that the signatures of the Hubbard Model in the strongly interacting regime can be simulated by modifying the screening in the limit of zero wavevector in Projector-Augmented Wave GW calculations for systems without significant nesting. This modification, when applied to the Mott insulator CuO, results in the opening of the Mott gap by the splitting of states at the Fermi level into upper and lower Hubbard bands, and exhibits a giant transfer of spectral weight upon electron doping. The method is also employed to clearly illustrate that the M{sub 1} and M{sub 2} forms of vanadium dioxide are fundamentally different types of insulator. Standard GW calculations are sufficient to open a gap in M{sub 1} VO{sub 2}, which arise from the Peierls pairing filling the valence band, creating homopolar bonds. The valence band wavefunctions are stabilized with respect to the conduction band, reducing polarizability and pushing the conduction band eigenvalues to higher energy. The M{sub 2} structure, however, opens a gap from strong on-site interactions; it is a Mott insulator.

Competition between Bose-Einstein Condensation and Spin Dynamics.

Science.gov (United States)

Naylor, B; Brewczyk, M; Gajda, M; Gorceix, O; Maréchal, E; Vernac, L; Laburthe-Tolra, B

2016-10-28

We study the impact of spin-exchange collisions on the dynamics of Bose-Einstein condensation by rapidly cooling a chromium multicomponent Bose gas. Despite relatively strong spin-dependent interactions, the critical temperature for Bose-Einstein condensation is reached before the spin degrees of freedom fully thermalize. The increase in density due to Bose-Einstein condensation then triggers spin dynamics, hampering the formation of condensates in spin-excited states. Small metastable spinor condensates are, nevertheless, produced, and they manifest in strong spin fluctuations.

Hypergeometric continuation of divergent perturbation series: II. Comparison with Shanks transformation and Padé approximation

Science.gov (United States)

Sanders, Sören; Holthaus, Martin

2017-11-01

We explore in detail how analytic continuation of divergent perturbation series by generalized hypergeometric functions is achieved in practice. Using the example of strong-coupling perturbation series provided by the two-dimensional Bose-Hubbard model, we compare hypergeometric continuation to Shanks and Padé techniques, and demonstrate that the former yields a powerful, efficient and reliable alternative for computing the phase diagram of the Mott insulator-to-superfluid transition. In contrast to Shanks transformations and Padé approximations, hypergeometric continuation also allows us to determine the exponents which characterize the divergence of correlation functions at the transition points. Therefore, hypergeometric continuation constitutes a promising tool for the study of quantum phase transitions.

Bose form of two-dimensional quantum chromodynamics

Energy Technology Data Exchange (ETDEWEB)

Baluni, V [Institute for Advanced Study, Princeton, NJ (USA); Stanford Linear Accelerator Center, CA (USA))

1980-03-01

By means of a special choice of gauge QCD/sub 2/(SU(N)) with one flavor of quarks is recast into the Bose form. Weak (g < m) and strong (g > m) coupling regimes are studied. The former is shown to be the SU(N)-symmetric confining phase in which bound states possess stringlike configurations with strings being represented by electric vortex lines; the ordinary mesons and baryons appear as longitudinal modes of electric strings. The strong coupling regime describes the Higgs phase with the residual symmetry (U(1))/sup N-1/ S/sub N/ where the left and right factors are the maximal abelian subgroup of SU(N) and the permutation group of N quarks, respectively; the particle spectrum consists of S/sub N/ multiplets adn the (U(1))/sup N-1/ charges are trapped.

Spectral properties of an extended Hubbard ladder with long range anti-ferromagnetic order

Science.gov (United States)

Yang, Chun; Feiguin, Adrian

We study the spectral properties of a Hubbard ladder with anti-ferromagnetic long range order by introducing a staggered Heisenberg interaction that decays algebraically. Unlike an alternating field or the t -Jz model, our problem preserves both SU (2) and translational invariance. We solve the problem with the time-dependent density matrix renormalization group and analyze the binding between holons and spinons and the structure of the elementary excitations. We discuss the implications in the context of the 2D Hubbard model at, and away from half-filling by using cluster perturbation theory (CPT). AF acknowledges the U.S. Department of Energy, Office of Basic Energy Sciences, for support under Grant DE-SC0014407.

Gutzwiller variational wave function for a two-orbital Hubbard model on a square lattice

Energy Technology Data Exchange (ETDEWEB)

Muenster, Kevin Torben zu

2015-07-01

freedom of the Gutzwiller correlator. Furthermore, we discussed the implications of this parameter gauge for a more general setup. The big advantage of our diagrammatic approach lies in the fact that it simplifies decisively in the limit of infinite spatial dimensions. We obtain the exact result for Gutzwiller expectation values of single-site and two-site operators without calculating a single, non-trivial diagram. Of course, the diagrams with internal vertices contribute in finite dimensions, and their importance for phase transitions and the Fermi surface has to be studied. In the chapter 3, we therefore investigated a two-band Hubbard model on a square lattice. We introduced the Hamiltonian for two degenerate p{sub x}-p{sub y} (or d{sub xy}-d{sub yz}) orbitals where we considered electron transfers between nearest neighbors and next-nearest neighbors. The orbital degeneracy reduces the number of different hopping parameters but transitions between the two orbitals are still permitted, i.e., the local orbital quantum number is not conserved in the lattice. For two degenerate orbitals, all local Coulomb interactions can be expressed in terms of the Hubbard interaction U and the Hund's-rule coupling J. The Hubbard interaction suppresses charge fluctuations in the lattice, and the Hund's rule coupling tends to maximize the local spin. We incorporated the symmetry constraints in the Gutzwiller variational states. As our first application, we studied the ferromagnetic phase transition as a function of the model parameters for various band fillings. In general, a large density of states and a strong Hund's-rule exchange favor ferromagnetism. In the Gutzwiller wave function, the ferromagnetic order is strongly suppressed so that much larger interaction strength are needed than predicted by the Hartree-Fock solution. Moreover, the regions in parameter space where non-saturated ferromagnetism occurs are much broader in Gutzwiller theory. As shown in earlier

Algebra of orthofermions and equivalence of their thermodynamics to the infinite U Hubbard model

International Nuclear Information System (INIS)

Kishore, R.; Mishra, A.K.

2006-01-01

The equivalence of thermodynamics of independent orthofermions to the infinite U Hubbard model, shown earlier for the one-dimensional infinite lattice, has been extended to a finite system of two lattice sites. Regarding the algebra of orthofermions, the algebraic expressions for the number operator for a given spin and the spin raising (lowering) operators in the form of infinite series are rearranged in such a way that the ith term, having the form of an infinite series, of the number (spin raising (lowering)) operator represents the number (spin raising (lowering)) operator at the ith lattice site

Symmetry-projected variational approach to the one-dimensional Hubbard model

International Nuclear Information System (INIS)

Schmid, K.W.; Dahm, T.; Margueron, J.; Muether, H.

2005-01-01

We apply a variational method devised for the nuclear many-body problem to the one-dimensional Hubbard model with nearest neighbor hopping and periodic boundary conditions. The test wave function consist for each state out of a single Hartree-Fock determinant mixing all the sites (or momenta) as well as the spin projections of the electrons. Total spin and linear momentum are restored by projection methods before the variation. It is demonstrated that this approach reproduces the results of exact diagonalizations for half-filled N=12 and N=14 lattices not only for the energies and occupation numbers of the ground but also of the lowest excited states rather well. Furthermore, a system of ten electrons in an N=12 lattice is investigated and, finally, an N=30 lattice is studied. In addition to energies and occupation numbers we present the spectral functions computed with the help of the symmetry-projected wave functions as well

Interaction quantum quenches in the one-dimensional Fermi-Hubbard model

Science.gov (United States)

Heidrich-Meisner, Fabian; Bauer, Andreas; Dorfner, Florian; Riegger, Luis; Orso, Giuliano

2016-05-01

We discuss the nonequilibrium dynamics in two interaction quantum quenches in the one-dimensional Fermi-Hubbard model. First, we study the decay of the Néel state as a function of interaction strength. We observe a fast charge dynamics over which double occupancies are built up, while the long-time decay of the staggered moment is controlled by spin excitations, corroborated by the analysis of the entanglement dynamics. Second, we investigate the formation of Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) correlations in a spin-imbalanced system in quenches from the noninteracting case to attractive interactions. Even though the quench puts the system at a finite energy density, peaks at the characteristic FFLO quasimomenta are visible in the quasi-momentum distribution function, albeit with an exponential decay of s-wave pairing correlations. We also discuss the imprinting of FFLO correlations onto repulsively bound pairs and their rapid decay in ramps. Supported by the DFG (Deutsche Forschungsgemeinschaft) via FOR 1807.

Fermi hyper-netted chain theory on a lattice: The Hubbard model

International Nuclear Information System (INIS)

Wang, X.Q.; Wang, X.Q.G.; Fantoni, S.; Tosatti, E.; Yu Lu.

1990-02-01

We review a new lattice version of Fermi Hyper-Netted Chain method for the study of strongly interacting electrons. The ordinary paramagnetic and the spin density wave functions have been correlated with Jastrow-type and e-d correlations, and the corresponding FHNC equations for the pair distribution function, the one body density matrix and the staggered magnetization are discussed. Results for the 1D chain and 2D square lattice models are presented and compared with the available results obtained within Quantum Monte Carlo, variational Monte Carlo and exact diagonalization of a 4x4 Hubbard cluster. Particularly interesting are the strong effects of e-d correlations on E/Nt and on the momentum distribution as well as antiferromagnetic behavior away from half filling found in our FHNC calculations in agreement with other studies. (author). 35 refs, 8 figs, 2 tabs

Bright solitons in Bose-Fermi mixtures

International Nuclear Information System (INIS)

Karpiuk, Tomasz; Brewczyk, Miroslaw; RzaPewski, Kazimierz

2006-01-01

We consider the formation of bright solitons in a mixture of Bose and Fermi degenerate gases confined in a three-dimensional elongated harmonic trap. The Bose and Fermi atoms are assumed to effectively attract each other whereas bosonic atoms repel each other. Strong enough attraction between bosonic and fermionic components can change the character of the interaction within the bosonic cloud from repulsive to attractive making thus possible the generation of bright solitons in the mixture. On the other hand, such structures might be in danger due to the collapse phenomenon existing in attractive gases. We show, however, that under some conditions (defined by the strength of the Bose-Fermi components attraction) the structures which neither spread nor collapse can be generated. For elongated enough traps the formation of solitons is possible even at the 'natural' value of the mutual Bose-Fermi ( 87 Rb- 40 K in our case) scattering length

Hubbard-U band-structure methods

DEFF Research Database (Denmark)

Albers, R.C.; Christensen, Niels Egede; Svane, Axel

2009-01-01

The last decade has seen a large increase in the number of electronic-structure calculations that involve adding a Hubbard term to the local-density approximation band-structure Hamiltonian. The Hubbard term is then determined either at the mean-field level or with sophisticated many......-body techniques such as using dynamical mean-field theory. We review the physics underlying these approaches and discuss their strengths and weaknesses in terms of the larger issues of electronic structure that they involve. In particular, we argue that the common assumptions made to justify such calculations...

Effects of measurement backaction in the stabilization of a Bose-Einstein condensate through feedback

International Nuclear Information System (INIS)

Wilson, S. D.; James, M. R.; Carvalho, A. R. R.; Hope, J. J.

2007-01-01

We apply quantum filtering and control to a particle in a harmonic trap under continuous position measurement, and show that a simple static feedback law can be used to cool the system. The final steady state is Gaussian and dependent on the feedback strength and coupling between the system and probe. In the limit of weak coupling, this final state becomes the ground state. An earlier model by Haine et al. [Phys. Rev. A 69, 13605 (2004)] without measurement backaction showed dark states: states that did not display error signals, thus remaining unaffected by the control. This paper shows that for a realistic measurement process this is not true, which indicates that a Bose-Einstein condensate may be driven toward the ground state from any arbitrary initial state

Bose-Einstein condensates form in heuristics learned by ciliates deciding to signal 'social' commitments.

Science.gov (United States)

Clark, Kevin B

2010-03-01

previous work demonstrating ciliates with improving expertise search grouped 'courting' assurances at quantum efficiencies and verify efficient processing by primitive 'social' intelligences involves network forms of Bose-Einstein condensation coupled to preceding thermodynamic-sensitive computational phases. 2009 Elsevier Ireland Ltd. All rights reserved.

Thermodynamic Properties of a Trapped Interacting Bose Gas

OpenAIRE

Shi, Hualin; Zheng, Wei-Mou

1996-01-01

A Bose gas in an external potential is studied by means of the local density approximation. Analytical results are derived for the thermodynamic properties of an ideal Bose gas in a generic power-law trapping potential, and their dependence on the mutual interaction of atoms in the case of a non-ideal Bose gas.

Real-time observation of fluctuations in a driven-dissipative quantum many-body system undergoing a phase transition

Science.gov (United States)

Donner, Tobias

2015-03-01

A Bose-Einstein condensate whose motional degrees of freedom are coupled to a high-finesse optical cavity via a transverse pump beam constitutes a dissipative quantum many-body system with long range interactions. These interactions can induce a structural phase transition from a flat to a density-modulated state. The transverse pump field simultaneously represents a probe of the atomic density via cavity- enhanced Bragg scattering. By spectrally analyzing the light field leaking out of the cavity, we measure non-destructively the dynamic structure factor of the fluctuating atomic density while the system undergoes the phase transition. An observed asymmetry in the dynamic structure factor is attributed to the coupling to dissipative baths. Critical exponents for both sides of the phase transition can be extracted from the data. We further discuss our progress in adding strong short-range interactions to this system, in order to explore Bose-Hubbard physics with cavity-mediated long-range interactions and self-organization in lower dimensions.

Solving Coupled Gross--Pitaevskii Equations on a Cluster of PlayStation 3 Computers

Science.gov (United States)

Edwards, Mark; Heward, Jeffrey; Clark, C. W.

2009-05-01

At Georgia Southern University we have constructed an 8+1--node cluster of Sony PlayStation 3 (PS3) computers with the intention of using this computing resource to solve problems related to the behavior of ultra--cold atoms in general with a particular emphasis on studying bose--bose and bose--fermi mixtures confined in optical lattices. As a first project that uses this computing resource, we have implemented a parallel solver of the coupled time--dependent, one--dimensional Gross--Pitaevskii (TDGP) equations. These equations govern the behavior of dual-- species bosonic mixtures. We chose the split--operator/FFT to solve the coupled 1D TDGP equations. The fast Fourier transform component of this solver can be readily parallelized on the PS3 cpu known as the Cell Broadband Engine (CellBE). Each CellBE chip contains a single 64--bit PowerPC Processor Element known as the PPE and eight ``Synergistic Processor Element'' identified as the SPE's. We report on this algorithm and compare its performance to a non--parallel solver as applied to modeling evaporative cooling in dual--species bosonic mixtures.

Bose enhancement and the ridge

Energy Technology Data Exchange (ETDEWEB)

Altinoluk, Tolga [Departamento de Física de Partículas and IGFAE, Universidade de Santiago de Compostela, 15706 Santiago de Compostela, Galicia (Spain); Armesto, Néstor, E-mail: nestor.armesto@usc.es [Departamento de Física de Partículas and IGFAE, Universidade de Santiago de Compostela, 15706 Santiago de Compostela, Galicia (Spain); Beuf, Guillaume [Department of Physics, Ben-Gurion University of the Negev, Beer Sheva 84105 (Israel); Kovner, Alex [Physics Department, University of Connecticut, 2152 Hillside Road, Storrs, CT 06269-3046 (United States); Lublinsky, Michael [Department of Physics, Ben-Gurion University of the Negev, Beer Sheva 84105 (Israel)

2015-12-17

We point out that Bose enhancement in a hadronic wave function generically leads to correlations between produced particles. We show explicitly, by calculating the projectile density matrix in the Color Glass Condensate approach to high-energy hadronic collisions, that the Bose enhancement of gluons in the projectile leads to azimuthal collimation of long range rapidity correlations of the produced particles, the so-called ridge correlations.

Excitonic Order and Superconductivity in the Two-Orbital Hubbard Model: Variational Cluster Approach

Science.gov (United States)

Fujiuchi, Ryo; Sugimoto, Koudai; Ohta, Yukinori

2018-06-01

Using the variational cluster approach based on the self-energy functional theory, we study the possible occurrence of excitonic order and superconductivity in the two-orbital Hubbard model with intra- and inter-orbital Coulomb interactions. It is known that an antiferromagnetic Mott insulator state appears in the regime of strong intra-orbital interaction, a band insulator state appears in the regime of strong inter-orbital interaction, and an excitonic insulator state appears between them. In addition to these states, we find that the s±-wave superconducting state appears in the small-correlation regime, and the dx2 - y2-wave superconducting state appears on the boundary of the antiferromagnetic Mott insulator state. We calculate the single-particle spectral function of the model and compare the band gap formation due to the superconducting and excitonic orders.

Analog model of a Friedmann-Robertson-Walker universe in Bose-Einstein condensates: Application of the classical field method

International Nuclear Information System (INIS)

Jain, Piyush; Weinfurtner, Silke; Visser, Matt; Gardiner, C. W.

2007-01-01

Analog models of gravity have been motivated by the possibility of investigating phenomena not readily accessible in their cosmological counterparts. In this paper, we investigate the analog of cosmological particle creation in a Friedmann-Robertson-Walker universe by numerically simulating a Bose-Einstein condensate with a time-dependent scattering length. In particular, we focus on a two-dimensional homogeneous condensate using the classical field method via the truncated Wigner approximation. We show that for various forms of the scaling function the particle production is consistent with the underlying theory in the long wavelength limit. In this context, we further discuss the implications of modified dispersion relations that arise from the microscopic theory of a weakly interacting Bose gas

Quench dynamics of the interacting Bose gas in one dimension.

Science.gov (United States)

Iyer, Deepak; Andrei, Natan

2012-09-14

We obtain an exact expression for the time evolution of the interacting Bose gas following a quench from a generic initial state using the Yudson representation for integrable systems. We study the time evolution of the density and noise correlation for a small number of bosons and their asymptotic behavior for any number. We show that for any value of the coupling, as long as it is repulsive, the system asymptotes towards a strongly repulsive gas, while for any value of an attractive coupling the long time behavior is dominated by the maximal bound state. This occurs independently of the initial state and can be viewed as an emerging "dynamic universality."

Evolution of the low-energy excitation spectrum from the pure Hubbard ladder to the SO(5) ladder: A numerical study

International Nuclear Information System (INIS)

Duffy, D.; Haas, S.; Kim, E.

1998-01-01

The Hubbard Hamiltonian on a two-leg ladder is studied numerically using quantum Monte Carlo and exact diagonalization techniques. A rung interaction, V, is turned on such that the resulting model has an exact SO(5) symmetry when V=-U. The evolution of the low-energy excitation spectrum is presented from the pure Hubbard ladder to the SO(5) ladder. It is shown that the low-energy excitations in the pure Hubbard ladder have an approximate SO(5) symmetry. copyright 1998 The American Physical Society

Trapped Fermions with Density Imbalance in the Bose-Einstein Condensate Limit

International Nuclear Information System (INIS)

Pieri, P.; Strinati, G.C.

2006-01-01

We analyze the effects of imbalancing the populations of two-component trapped fermions, in the Bose-Einstein condensate limit of the attractive interaction between different fermions. Starting from the gap equation with two fermionic chemical potentials, we derive a set of coupled equations that describe composite bosons and excess fermions. We include in these equations the processes leading to the correct dimer-dimer and dimer-fermion scattering lengths. The coupled equations are then solved in the Thomas-Fermi approximation to obtain the density profiles for composite bosons and excess fermions, which are relevant to the recent experiments with trapped fermionic atoms

Diagram analysis of the Hubbard model: Stationarity property of the thermodynamic potential

International Nuclear Information System (INIS)

Moskalenko, V. A.; Dohotaru, L. A.; Cebotari, I. D.

2010-01-01

The diagram approach proposed many years ago for the strongly correlated Hubbard model is developed with the aim to analyze the thermodynamic potential properties. A new exact relation between renormalized quantities such as the thermodynamic potential, the one-particle propagator, and the correlation function is established. This relation contains an additional integration of the one-particle propagator with respect to an auxiliary constant. The vacuum skeleton diagrams constructed from the irreducible Green's functions and tunneling propagator lines are determined and a special functional is introduced. The properties of this functional are investigated and its relation to the thermodynamic potential is established. The stationarity property of this functional with respect to first-order variations of the correlation function is demonstrated; as a consequence, the stationarity property of the thermodynamic potential is proved.

Hypergeometric continuation of divergent perturbation series: I. Critical exponents of the Bose–Hubbard model

International Nuclear Information System (INIS)

Sanders, Sören; Holthaus, Martin

2017-01-01

We study the connection between the exponent of the order parameter of the Mott insulator-to-superfluid transition occurring in the two-dimensional Bose–Hubbard model, and the divergence exponents of its one- and two-particle correlation functions. We find that at the multicritical points all divergence exponents are related to each other, allowing us to express the critical exponent in terms of one single divergence exponent. This approach correctly reproduces the critical exponent of the three-dimensional XY universality class. Because divergence exponents can be computed in an efficient manner by hypergeometric analytic continuation, our strategy is applicable to a wide class of systems. (paper)

Bose enhancement and the ridge

Directory of Open Access Journals (Sweden)

Tolga Altinoluk

2015-12-01

Full Text Available We point out that Bose enhancement in a hadronic wave function generically leads to correlations between produced particles. We show explicitly, by calculating the projectile density matrix in the Color Glass Condensate approach to high-energy hadronic collisions, that the Bose enhancement of gluons in the projectile leads to azimuthal collimation of long range rapidity correlations of the produced particles, the so-called ridge correlations.

Localization of weakly interacting Bose gas in quasiperiodic potential

International Nuclear Information System (INIS)

Ray, Sayak; Pandey, Mohit; Ghosh, Anandamohan; Sinha, Subhasis

2016-01-01

We study the localization properties of weakly interacting Bose gas in a quasiperiodic potential. The Hamiltonian of the non-interacting system reduces to the well known ‘Aubry–André model’, which shows the localization transition at a critical strength of the potential. In the presence of repulsive interaction we observe multi-site localization and obtain a phase diagram of the dilute Bose gas by computing the superfluid fraction and the inverse participation ratio. We construct a low-dimensional classical Hamiltonian map and show that the onset of localization is manifested by the chaotic phase space dynamics. The level spacing statistics also identify the transition to localized states resembling a Poisson distribution that are ubiquitous for both non-interacting and interacting systems. We also study the quantum fluctuations within the Bogoliubov approximation and compute the quasiparticle energy spectrum. Enhanced quantum fluctuation and multi-site localization phenomenon of non-condensate density are observed above the critical coupling of the potential. We briefly discuss the effect of the trapping potential on the localization of matter wave. (paper)

Bose-Einstein-condensed gases with arbitrary strong interactions

International Nuclear Information System (INIS)

Yukalov, V. I.; Yukalova, E. P.

2006-01-01

Bose-condensed gases are considered with an effective interaction strength varying in the whole range of the values between zero and infinity. The consideration is based on the usage of a representative statistical ensemble for Bose systems with broken global gauge symmetry. Practical calculations are illustrated for a uniform Bose gas at zero temperature, employing a self-consistent mean-field theory, which is both conserving and gapless

Ferroelectricity by Bose-Einstein condensation in a quantum magnet.

Science.gov (United States)

Kimura, S; Kakihata, K; Sawada, Y; Watanabe, K; Matsumoto, M; Hagiwara, M; Tanaka, H

2016-09-26

The Bose-Einstein condensation is a fascinating phenomenon, which results from quantum statistics for identical particles with an integer spin. Surprising properties, such as superfluidity, vortex quantization or Josephson effect, appear owing to the macroscopic quantum coherence, which spontaneously develops in Bose-Einstein condensates. Realization of Bose-Einstein condensation is not restricted in fluids like liquid helium, a superconducting phase of paired electrons in a metal and laser-cooled dilute alkali atoms. Bosonic quasi-particles like exciton-polariton and magnon in solids-state systems can also undergo Bose-Einstein condensation in certain conditions. Here, we report that the quantum coherence in Bose-Einstein condensate of the magnon quasi particles yields spontaneous electric polarization in the quantum magnet TlCuCl 3 , leading to remarkable magnetoelectric effect. Very soft ferroelectricity is realized as a consequence of the O(2) symmetry breaking by magnon Bose-Einstein condensation. The finding of this ferroelectricity will open a new window to explore multi-functionality of quantum magnets.

Coexistence of photonic and atomic Bose-Einstein condensates in ideal atomic gases

Directory of Open Access Journals (Sweden)

N. Boichenko

2015-12-01

Full Text Available We have studied conditions of photon Bose-Einstein condensate formation that is in thermodynamic equilibrium with ideal gas of two-level Bose atoms below the degeneracy temperature. Equations describing thermodynamic equilibrium in the system were formulated; critical temperatures and densities of photonic and atomic gas subsystems were obtained analytically. Coexistence conditions of these photonic and atomic Bose-Einstein condensates were found. There was predicted the possibility of an abrupt type of photon condensation in the presence of Bose condensate of ground-state atoms: it was shown that the slightest decrease of the temperature could cause a significant gathering of photons in the condensate. This case could be treated as a simple model of the situation known as "stopped light" in cold atomic gas. We also showed how population inversion of atomic levels can be created by lowering the temperature. The latter situation looks promising for light accumulation in atomic vapor at very low temperatures.

Condensate statistics in interacting and ideal dilute bose gases

Science.gov (United States)

Kocharovsky; Kocharovsky; Scully

2000-03-13

We obtain analytical formulas for the statistics, in particular, for the characteristic function and all cumulants, of the Bose-Einstein condensate in dilute weakly interacting and ideal equilibrium gases in the canonical ensemble via the particle-number-conserving operator formalism of Girardeau and Arnowitt. We prove that the ground-state occupation statistics is not Gaussian even in the thermodynamic limit. We calculate the effect of Bogoliubov coupling on suppression of ground-state occupation fluctuations and show that they are governed by a pair-correlation, squeezing mechanism.

Thermodynamic identities and particle number fluctuations in weakly interacting Bose-Einstein condensates

Energy Technology Data Exchange (ETDEWEB)

Illuminati, Fabrizio [Institut fuer Physik, Universitaet Potsdam, Am Neuen Palais 10, D-14415, Potsdam (Germany); Dipartimento di Fisica, Universita di Salerno, and INFM, Unita di Salerno, I-84081 Baronissi SA (Italy); Navez, Patrick [Institut fuer Physik, Universitaet Potsdam, Am Neuen Palais 10, D-14415, Potsdam (Germany); Institute of Materials Science, Demokritos NCSR, POB 60228, 15310 Athens (Greece); Wilkens, Martin [Institut fuer Physik, Universitaet Potsdam, Am Neuen Palais 10, D-14415, Potsdam (Germany)

1999-08-14

We derive exact thermodynamic identities relating the average number of condensed atoms and the root-mean-square fluctuations determined in different statistical ensembles for the weakly interacting Bose gas confined in a box. This is achieved by introducing the concept of auxiliary partition functions for model Hamiltonians that do conserve the total number of particles. Exploiting such thermodynamic identities, we provide the first, completely analytical prediction of the microcanonical particle number fluctuations in the weakly interacting Bose gas. Such fluctuations, as a function of the volume V of the box are found to behave normally, in contrast with the anomalous scaling behaviour V{sup 4/3} of the fluctuations in the ideal Bose gas. (author). Letter-to-the-editor.

Time-evolution of entanglement and Greenberger-Horne-Zeilinger states in two-mode Bose-Einstein condensates

International Nuclear Information System (INIS)

Yin Wen; Zhang, G.-F.; Liang, J.-Q.; Yan, Q.-W.

2004-01-01

In this Brief Report we investigate the time evolution of entanglement in two-mode Bose-Einstein condensates (BEC's) with various parameters of the scattering lengths of interatoms collisions, Josephson coupling strength, and initial states. The degree of entanglement increases by strengthening the tunnel coupling and keeping the balance of the collision interaction. In the latter stage we show that the two-mode BEC's can be used for preparing the Greenberger-Home-Zeilinger state

Algebraic approach to q-deformed supersymmetric variants of the Hubbard model with pair hoppings

International Nuclear Information System (INIS)

Arnaudon, D.

1997-01-01

Two quantum spin chains Hamiltonians with quantum sl(2/1) invariance are constructed. These spin chains define variants of the Hubbard model and describe electron models with pair hoppings. A cubic algebra that admits the Birman-Wenzl-Murakami algebra as a quotient allows exact solvability of the periodic chain. The two Hamiltonians, respectively built using the distinguished and the fermionic bases of U q (sl(2/1)) differ only in the boundary terms. They are actually equivalent, but the equivalence is non local. Reflection equations are solved to get exact solvability on open chains with non trivial boundary conditions. Two families of diagonal solutions are found. The centre and the s-Casimir of the quantum enveloping algebra of sl(2/1) appear as tools for the construction of exactly solvable Hamiltonians. (author)

Finite-temperature models of Bose-Einstein condensation

Energy Technology Data Exchange (ETDEWEB)

Proukakis, Nick P; Jackson, Brian [School of Mathematics and Statistics, Newcastle University, Newcastle-upon-Tyne NE1 7RU (United Kingdom)], E-mail: Nikolaos.Proukakis@ncl.ac.uk

2008-10-28

The theoretical description of trapped weakly interacting Bose-Einstein condensates is characterized by a large number of seemingly very different approaches which have been developed over the course of time by researchers with very distinct backgrounds. Newcomers to this field, experimentalists and young researchers all face a considerable challenge in navigating through the 'maze' of abundant theoretical models, and simple correspondences between existing approaches are not always very transparent. This tutorial provides a generic introduction to such theories, in an attempt to single out common features and deficiencies of certain 'classes of approaches' identified by their physical content, rather than their particular mathematical implementation. This tutorial is structured in a manner accessible to a non-specialist with a good working knowledge of quantum mechanics. Although some familiarity with concepts of quantum field theory would be an advantage, key notions, such as the occupation number representation of second quantization, are nonetheless briefly reviewed. Following a general introduction, the complexity of models is gradually built up, starting from the basic zero-temperature formalism of the Gross-Pitaevskii equation. This structure enables readers to probe different levels of theoretical developments (mean field, number conserving and stochastic) according to their particular needs. In addition to its 'training element', we hope that this tutorial will prove useful to active researchers in this field, both in terms of the correspondences made between different theoretical models, and as a source of reference for existing and developing finite-temperature theoretical models. (phd tutorial)

Non local theory of excitations applied to the Hubbard model

International Nuclear Information System (INIS)

Kakehashi, Y; Nakamura, T; Fulde, P

2010-01-01

We propose a nonlocal theory of single-particle excitations. It is based on an off-diagonal effective medium and the projection operator method for treating the retarded Green function. The theory determines the nonlocal effective medium matrix elements by requiring that they are consistent with those of the self-energy of the Green function. This arrows for a description of long-range intersite correlations with high resolution in momentum space. Numerical study for the half-filled Hubbard model on the simple cubic lattice demonstrates that the theory is applicable to the strong correlation regime as well as the intermediate regime of Coulomb interaction strength. Furthermore the results show that nonlocal excitations cause sub-bands in the strong Coulomb interaction regime due to strong antiferromagnetic correlations, decrease the quasi-particle peak on the Fermi level with increasing Coulomb interaction, and shift the critical Coulomb interaction U C2 for the divergence of effective mass towards higher energies at least by a factor of two as compared with that in the single-site approximation.

More accurate theory for Bose-Einstein condensation fraction

International Nuclear Information System (INIS)

Biswas, Shyamal

2008-01-01

Bose-Einstein statistics is derived in the thermodynamic limit when the ratio of system size to thermal de Broglie wavelength goes to infinity. However, according to the experimental setup of Bose-Einstein condensation of harmonically trapped Bose gas of alkali atoms, the ratio near the condensation temperature (T o ) is 30-50. And, at ultralow temperatures well below T o , this ratio becomes comparable to 1. We argue that finite size as well as the ultralow temperature induces corrections to Bose-Einstein statistics. From the corrected statistics we plot condensation fraction versus temperature graph. This theoretical plot satisfies well with the experimental plot [A. Griesmaier et al., Phys. Rev. Lett. 94 (2005) 160401

Soliton resonance in bose-einstein condensate

Science.gov (United States)

Zak, Michail; Kulikov, I.

2002-01-01

A new phenomenon in nonlinear dispersive systems, including a Bose-Einstein Condensate (BEC), has been described. It is based upon a resonance between an externally induced soliton and 'eigen-solitons' of the homogeneous cubic Schrodinger equation. There have been shown that a moving source of positive /negative potential induces bright /dark solitons in an attractive / repulsive Bose condensate.

Generating entangled state of Bose-Einstein condensate using electromagnetically induced transparency

Science.gov (United States)

Li, Song-Song

2018-01-01

We put forward a scheme on how to generate entangled state of Bose-Einstein condensate (BEC) using electromagnetically induced transparency (EIT). It is shown that we can rapidly generate the entangled state in the dynamical process and the entangled state maintained a long time interval. It is also shown that the better entangled state can be generated by decreasing coupling strengths of two classical laser fields, increasing two-photon detuning and total number of atoms.

Phase diagram and topological phases in the triangular lattice Kitaev-Hubbard model

Science.gov (United States)

Li, Kai; Yu, Shun-Li; Gu, Zhao-Long; Li, Jian-Xin

2016-09-01

We study the half-filled Hubbard model on a triangular lattice with spin-dependent Kitaev-like hopping. Using the variational cluster approach, we identify five phases: a metallic phase, a non-coplanar chiral magnetic order, a 120° magnetic order, a nonmagnetic insulator (NMI), and an interacting Chern insulator (CI) with a nonzero Chern number. The transition from CI to NMI is characterized by the change of the charge gap from an indirect band gap to a direct Mott gap. Based on the slave-rotor mean-field theory, the NMI phase is further suggested to be a gapless Mott insulator with a spinon Fermi surface or a fractionalized CI with nontrivial spinon topology, depending on the strength of the Kitaev-like hopping. Our work highlights the rising field in which interesting phases emerge from the interplay between band topology and Mott physics.

Multistability in an optomechanical system with a two-component Bose-Einstein condensate

International Nuclear Information System (INIS)

Dong Ying; Ye Jinwu; Pu Han

2011-01-01

We investigate a system consisting of a two-component Bose-Einstein condensate interacting dispersively with a Fabry-Perot optical cavity where the two components of the condensate are resonantly coupled to each other by another classical field. The key feature of this system is that the atomic motional degrees of freedom and the internal pseudospin degrees of freedom are coupled to the cavity field simultaneously, hence an effective spin-orbital coupling within the condensate is induced by the cavity. The interplay among the atomic center-of-mass motion, the atomic collective spin, and the cavity field leads to a strong nonlinearity, resulting in multistable behavior in both matter wave and light wave at the few-photon level.

Exact equivalence between one-dimensional Bose gases interacting via hard-sphere and zero-range potentials

DEFF Research Database (Denmark)

Valiente, Manuel

2012-01-01

We prove the equivalence between the hard-sphere Bose gas and a system with momentum-dependent zero-range interactions in one spatial dimension, which we call extended hard-sphere Bose gas. The two-body interaction in the latter model has the advantage of being a regular pseudopotential. The most...

Dipolar oscillations in a quantum degenerate Fermi-Bose atomic mixture

International Nuclear Information System (INIS)

Ferlaino, F; Brecha, R J; Hannaford, P; Riboli, F; Roati, G; Modugno, G; Inguscio, M

2003-01-01

We study the dynamics of coupled dipolar oscillations in a Fermi-Bose mixture of 40 K and 87 Rb atoms. This low-energy collective mode is strongly affected by the interspecies interactions. Measurements are performed in the classical and quantum degenerate regimes and reveal the crucial role of the statistical properties of the mixture. At the onset of quantum degeneracy, we investigate the role of Pauli blocking and superfluidity for K and Rb atoms, respectively, resulting in a change in the collisional interactions

Spontaneous symmetry breaking in spinor Bose-Einstein condensates

DEFF Research Database (Denmark)

Scherer, Manuel; Lücke, Bernd; Peise, Jan

2013-01-01

We present an analytical model for the theoretical analysis of spin dynamics and spontaneous symmetry breaking in a spinor Bose-Einstein condensate (BEC). This allows for an excellent intuitive understanding of the processes and provides good quantitative agreement with the experimental results...

Atom-number squeezing and bipartite entanglement of two-component Bose-Einstein condensates: analytical results

Energy Technology Data Exchange (ETDEWEB)

Jin, G R; Wang, X W; Li, D; Lu, Y W, E-mail: grjin@bjtu.edu.c [Department of Physics, Beijing Jiaotong University, Beijing 100044 (China)

2010-02-28

We investigate spin dynamics of a two-component Bose-Einstein condensate with weak Josephson coupling. Analytical expressions of atom-number squeezing and bipartite entanglement are presented for atom-atom repulsive interactions. For attractive interactions, there is no number squeezing; however, the squeezing parameter is still useful to recognize the appearance of Schroedinger's cat state.

Solitons, Bose-Einstein condensation and superfluidity in He II

International Nuclear Information System (INIS)

Chela-Flores, J.; Ghassib, H.B.

1985-09-01

The analytic form of a wave propagating with a constant velocity and a permanent profile is inferred for a weakly interacting Bose gas, using an exact (rather than asymptotic) solution of the field equation of the self-consistent Hartree model. The significance of this approach is indicated, especially when realistic interatomic potentials are used. In addition, the general relation between solitons and Bose-Einstein condensation is underlined by invoking the profound insight recently acquired in studies of the quantum liquids involved in the living state. It is concluded that solitons may occur in He II, and may play a significant role in the phenomena of superfluidity. (author)

Can disorder act as a chemical pressure? An optical study of the Hubbard model

Science.gov (United States)

Barman, H.; Laad, M. S.; Hassan, S. R.

2018-05-01

The optical properties have been studied using the dynamical mean-field theory on a disordered Hubbard model. Despite the fact that disorder turns a metal to an insulator in high dimensional correlated materials, we notice that it can enhance certain metallic behavior as if a chemical pressure is applied to the system resulting in an increase of the effective lattice bandwidth (BW). We study optical properties in such a scenario and compare results with experiments where the BW is changed through isovalent chemical substitution (keeping electron filling unaltered) and obtain remarkable similarities vindicating our claim. We also make the point that these similarities differ from some other forms of BW tuned optical effects.

Spectroscopy of dark soliton states in Bose-Einstein condensates

International Nuclear Information System (INIS)

Bongs, K; Burger, S; Hellweg, D; Kottke, M; Dettmer, S; Rinkleff, T; Cacciapuoti, L; Arlt, J; Sengstock, K; Ertmer, W

2003-01-01

Experimental and numerical studies of the velocity field of dark solitons in Bose-Einstein condensates are presented. The formation process after phase imprinting as well as the propagation of the emerging soliton are investigated using spatially resolved Bragg spectroscopy of soliton states in Bose-Einstein condensates of 87 Rb. A comparison of experimental data to results from numerical simulations of the Gross-Pitaevskii equation clearly identifies the flux underlying a dark soliton propagating in a Bose-Einstein condensate. The results allow further optimization of the phase imprinting method for creating collective excitations of Bose-Einstein condensates

Emergent Chiral Spin State in the Mott Phase of a Bosonic Kane-Mele-Hubbard Model

Science.gov (United States)

Plekhanov, Kirill; Vasić, Ivana; Petrescu, Alexandru; Nirwan, Rajbir; Roux, Guillaume; Hofstetter, Walter; Le Hur, Karyn

2018-04-01

Recently, the frustrated X Y model for spins 1 /2 on the honeycomb lattice has attracted a lot of attention in relation with the possibility to realize a chiral spin liquid state. This model is relevant to the physics of some quantum magnets. Using the flexibility of ultracold atom setups, we propose an alternative way to realize this model through the Mott regime of the bosonic Kane-Mele-Hubbard model. The phase diagram of this model is derived using bosonic dynamical mean-field theory. Focusing on the Mott phase, we investigate its magnetic properties as a function of frustration. We do find an emergent chiral spin state in the intermediate frustration regime. Using exact diagonalization we study more closely the physics of the effective frustrated X Y model and the properties of the chiral spin state. This gapped phase displays a chiral order, breaking time-reversal and parity symmetry, but is not topologically ordered (the Chern number is zero).

Approximation auto-coherente a deux particules, pseudogap et supraconductivite dans le modele de Hubbard attractif

Science.gov (United States)

Allen, Steve

2000-10-01

Dans cette these nous presentons une nouvelle methode non perturbative pour le calcul des proprietes d'un systeme de fermions. Notre methode generalise l'approximation auto-coherente a deux particules proposee par Vilk et Tremblay pour le modele de Hubbard repulsif. Notre methode peut s'appliquer a l'etude du comportement pre-critique lorsque la symetrie du parametre d'ordre est suffisamment elevee. Nous appliquons la methode au probleme du pseudogap dans le modele de Hubbard attractif. Nos resultats montrent un excellent accord avec les donnees Monte Carlo pour de petits systemes. Nous observons que le regime ou apparait le pseudogap dans le poids spectral a une particule est un regime classique renormalise caracterise par une frequence caracteristique des fluctuations supraconductrices inferieure a la temperature. Une autre caracteristique est la faible densite de superfluide de cette phase demontrant que nous ne sommes pas en presence de paires preformees. Les resultats obtenus semblent montrer que la haute symetrie du parametre d'ordre et la bidimensionalite du systeme etudie elargissent le domaine de temperature pour lequel le regime pseudogap est observe. Nous argumentons que ce resultat est transposable aux supraconducteurs a haute temperature critique ou le pseudogap apparait a des' temperatures beaucoup plus grandes que la temperature critique. La forte symetrie dans ces systemes pourraient etre reliee a la theorie SO(5) de Zhang. En annexe, nous demontrons un resultat tout recent qui permettrait d'assurer l'auto-coherence entre les proprietes a une et a deux particules par l'ajout d'une dynamique au vertex irreductible. Cet ajout laisse entrevoir la possibilite d'etendre la methode au cas d'une forte interaction.

Cavity-induced artificial gauge field in a Bose-Hubbard ladder

Science.gov (United States)

Halati, Catalin-Mihai; Sheikhan, Ameneh; Kollath, Corinna

2017-12-01

We consider theoretically ultracold interacting bosonic atoms confined to quasi-one-dimensional ladder structures formed by optical lattices and coupled to the field of an optical cavity. The atoms can collect a spatial phase imprint during a cavity-assisted tunneling along a rung via Raman transitions employing a cavity mode and a transverse running wave pump beam. By adiabatic elimination of the cavity field we obtain an effective Hamiltonian for the bosonic atoms, with a self-consistency condition. Using the numerical density-matrix renormalization-group method, we obtain a rich steady-state diagram of self-organized steady states. Transitions between superfluid to Mott-insulating states occur, on top of which we can have Meissner, vortex liquid, and vortex lattice phases. Also a state that explicitly breaks the symmetry between the two legs of the ladder, namely, the biased-ladder phase, is dynamically stabilized. We investigate the influence that a trapping potential has on the stability of the self-organized phases.

Classical region of a trapped Bose gas

Energy Technology Data Exchange (ETDEWEB)

Blakie, P Blair [Jack Dodd Centre for Photonics and Ultra-Cold Atoms, University of Otago, Dunedin (New Zealand); Davis, Matthew J [ARC Centre of Excellence for Quantum-Atom Optics, School of Physical Sciences, University of Queensland, Brisbane, QLD 4072 (Australia)

2007-06-14

The classical region of a Bose gas consists of all single particle modes that have a high average occupation and are well described by a classical field. Highly occupied modes only occur in massive Bose gases at ultra-cold temperatures, in contrast to the photon case where there are highly occupied modes at all temperatures. For the Bose gas the number of these modes is dependent on the temperature, the total number of particles and their interaction strength. In this paper, we characterize the classical region of a harmonically trapped Bose gas over a wide parameter regime. We use a Hartree-Fock approach to account for the effects of interactions, which we observe to significantly change the classical region as compared to the idealized case. We compare our results to full classical field calculations and show that the Hartree-Fock approach provides a qualitatively accurate description of a classical region for the interacting gas.

Bose condensation in 4He and neutron scattering

International Nuclear Information System (INIS)

Silver, R.N.

1997-01-01

The discovery of superfluidity in liquid 4 He below T λ = 2.17 K, and its phenomenological characterization since then, has been one of the great success stories of condensed matter physics. The relation of superfluidity to the behavior of atoms was conjectured by F. London in 1938. Superfluidity is a manifestation of the Bose condensation of helium atoms, the extensive occupation of the zero momentum state. Ever since 4 He has been the paradigm in the search for Bose condensates in other systems. At the Pune meeting scientists have heard exciting new evidence for Bose condensates of laser cooled alkali atoms in magnetic traps, of excitons in Cu 2 O, and possibly pre-formed Cooper pairs of electrons in the high T c perovskite superconductors. There remains the holy-grail of forming a Bose condensate in spin-polarized hydrogen. In the current excitement for new types of Bose condensates, and new phenomena such as atom lasers, it may be useful to recall the older story of the experimental verification of a relation between superfluidity and Bose condensation in 4 He. This topic has been investigated over many years by neutron scattering experiments and quantum many-body theory. The authors goal is to illustrate the difficulties of establishing the existence of a Bose condensate in a strongly interacting system, even though its macroscopic effects are manifest. The author assumes readers have access to a review by Silver and Sokol which emphasizes the neutron scattering theory through 1990 and a review by Snow and Sokol of the deep inelastic neutron scattering (DINS) experiments through 1995

Classical and quantum analysis of a hetero-triatomic molecular Bose-Einstein condensate model

International Nuclear Information System (INIS)

Tonel, A.P.; Kuhn, C.C.N.; Foerster, A.; Santos, G.; Roditi, I.; Santos, Z.V.T.

2014-11-01

We investigate an integrable Hamiltonian modelling a hetero-triatomic-molecular Bose-Einstein condensate. This model describes a mixture of two species of atoms in different proportions, which can combine to form a triatomic molecule. Beginning with a classical analysis, we determine the fixed points of the system. Bifurcations of these points separate the parameter space into different regions. Three distinct scenarios are found, varying with the atomic population imbalance. This result suggests the ground state properties of the quantum model exhibits a sensitivity on the atomic population imbalance, which is confirmed by a quantum analysis using different approaches, such as the ground-state expectation values, the behaviour of the quantum dynamics, the energy gap and the ground state fidelity. (author)

Optimal conversion of an atomic to a molecular Bose-Einstein condensate

International Nuclear Information System (INIS)

Hornung, Thomas; Gordienko, Sergei; Vivie-Riedle, Regina de; Verhaar, Boudewijn J.

2002-01-01

The work in this article extends the optimal control framework of variational calculus to optimize the conversion of a Bose-Einstein condensate of atoms to one of molecules. It represents the derivation of the closed form optimal control equations for a system governed by a nonlinear Schroedinger equation and its successful application. It was necessary to derive a density matrix formulation of the coupled Gross-Pitaevskii equations to optimize STIRAP-like Raman light fields, to overcome dissipation

Off-site interaction effect in the Extended Hubbard Model with the SCRPA method

International Nuclear Information System (INIS)

Harir, S; Bennai, M; Boughaleb, Y

2007-01-01

The self consistent random phase approximation (SCRPA) and a direct analytical (DA) method are proposed to solve the Extended Hubbard Model (EHM) in one dimension (1D). We have considered an EHM including on-site and off-site interactions for closed chains in 1D with periodic boundary conditions. The comparison of the SCRPA results with the ones obtained by a DA approach shows that the SCRPA treats the problem of these closed chains in a rigorous manner. The analysis of the nearest-neighbour repulsion effect on the dynamics of our closed chains shows that this repulsive interaction between the electrons of the neighbouring atoms induces supplementary conductivity, since, the SCRPA energygap vanishes when these closed chains are governed by a strong repulsive on-site interaction and intermediate nearest-neighbour repulsion

Off-equilibrium infrared structure of self-interacting scalar fields: Universal scaling, vortex-antivortex superfluid dynamics, and Bose-Einstein condensation

Science.gov (United States)

Deng, Jian; Schlichting, Soeren; Venugopalan, Raju; Wang, Qun

2018-05-01

We map the infrared dynamics of a relativistic single-component (N =1 ) interacting scalar field theory to that of nonrelativistic complex scalar fields. The Gross-Pitaevskii (GP) equation, describing the real-time dynamics of single-component ultracold Bose gases, is obtained at first nontrivial order in an expansion proportional to the powers of λ ϕ2/m2 where λ , ϕ , and m are the coupling constant, the scalar field, and the particle mass respectively. Our analytical studies are corroborated by numerical simulations of the spatial and momentum structure of overoccupied scalar fields in (2+1)-dimensions. Universal scaling of infrared modes, vortex-antivortex superfluid dynamics, and the off-equilibrium formation of a Bose-Einstein condensate are observed. Our results for the universal scaling exponents are in agreement with those extracted in the numerical simulations of the GP equation. As in these simulations, we observe coarsening phase kinetics in the Bose superfluid with strongly anomalous scaling exponents relative to that of vertex resummed kinetic theory. Our relativistic field theory framework further allows one to study more closely the coupling between superfluid and normal fluid modes, specifically the turbulent momentum and spatial structure of the coupling between a quasiparticle cascade to the infrared and an energy cascade to the ultraviolet. We outline possible applications of the formalism to the dynamics of vortex-antivortex formation and to the off-equilibrium dynamics of the strongly interacting matter formed in heavy-ion collisions.

The Mott transition in the strong coupling perturbation theory

Science.gov (United States)

Sherman, A.

2015-01-01

Using the strong coupling diagram technique a self-consistent equation for the electron Green's function is derived for the repulsive Hubbard model. Terms of two lowest orders of the ratio of the bandwidth Δ to the Hubbard repulsion U are taken into account in the irreducible part of the Larkin equation. The obtained equation is shown to retain causality and reduces to Green's function of uncorrelated electrons in the limit U → 0. Calculations were performed for the semi-elliptical initial band. It is shown that the approximation describes the Mott transition, which occurs at Uc =√{ 3 } Δ / 2. This value coincides with that obtained in the Hubbard-III approximation. At half-filling, for 0 self-energy is nonzero at the Fermi level, which indicates that the obtained solution is not a Fermi liquid. At small deviations from half-filling the density of states shifts along the frequency axis without perceptible changes in its shape. For larger deviations the density of states is modified: it is redistributed in favor of the subband, in which the Fermi level is located, and for U >Uc the Mott gap disappears.

On the particle-hole symmetry of the fermionic spinless Hubbard model in D=1

Directory of Open Access Journals (Sweden)

M.T. Thomaz

2014-06-01

Full Text Available We revisit the particle-hole symmetry of the one-dimensional (D=1 fermionic spinless Hubbard model, associating that symmetry to the invariance of the Helmholtz free energy of the one-dimensional spin-1/2 XXZ Heisenberg model, under reversal of the longitudinal magnetic field and at any finite temperature. Upon comparing two regimes of that chain model so that the number of particles in one regime equals the number of holes in the other, one finds that, in general, their thermodynamics is similar, but not identical: both models share the specific heat and entropy functions, but not the internal energy per site, the first-neighbor correlation functions, and the number of particles per site. Due to that symmetry, the difference between the first-neighbor correlation functions is proportional to the z-component of magnetization of the XXZ Heisenberg model. The results presented in this paper are valid for any value of the interaction strength parameter V, which describes the attractive/null/repulsive interaction of neighboring fermions.

Atomic-phase interference devices based on ring-shaped Bose-Einstein condensates: Two-ring case

International Nuclear Information System (INIS)

Anderson, B.P.; Dholakia, K.; Wright, E.M.

2003-01-01

We theoretically investigate the ground-state properties and quantum dynamics of a pair of adjacent ring-shaped Bose-Einstein condensates that are coupled via tunneling. This device, which is the analog of a symmetric superconducting quantum interference device, is the simplest version of what we term an atomic-phase interference device (APHID). The two-ring APHID is shown to be sensitive to rotation

Quench-Induced Breathing Mode of One-Dimensional Bose Gases

Science.gov (United States)

Fang, Bess; Carleo, Giuseppe; Johnson, Aisling; Bouchoule, Isabelle

2014-07-01

We measure the position- and momentum-space breathing dynamics of trapped one-dimensional Bose gases at finite temperature. The profile in real space reveals sinusoidal width oscillations whose frequency varies continuously through the quasicondensate to ideal Bose gas crossover. A comparison with theoretical models taking temperature into account is provided. In momentum space, we report the first observation of a frequency doubling in the quasicondensate regime, corresponding to a self-reflection mechanism due to the repulsive interactions. Such a mechanism is predicted for a fermionized system, and has not been observed to date. The disappearance of the frequency doubling through the crossover is mapped out experimentally, giving insights into the dynamics of the breathing evolution.

Quench-induced breathing mode of one-dimensional Bose gases.

Science.gov (United States)

Fang, Bess; Carleo, Giuseppe; Johnson, Aisling; Bouchoule, Isabelle

2014-07-18

We measure the position- and momentum-space breathing dynamics of trapped one-dimensional Bose gases at finite temperature. The profile in real space reveals sinusoidal width oscillations whose frequency varies continuously through the quasicondensate to ideal Bose gas crossover. A comparison with theoretical models taking temperature into account is provided. In momentum space, we report the first observation of a frequency doubling in the quasicondensate regime, corresponding to a self-reflection mechanism due to the repulsive interactions. Such a mechanism is predicted for a fermionized system, and has not been observed to date. The disappearance of the frequency doubling through the crossover is mapped out experimentally, giving insights into the dynamics of the breathing evolution.

Dynamical mean field study of the Mott transition in the half-filled Hubbard model on a triangular lattice

OpenAIRE

Aryanpour, K.; Pickett, W. E.; Scalettar, R. T.

2006-01-01

We employ dynamical mean field theory (DMFT) with a Quantum Monte Carlo (QMC) atomic solver to investigate the finite temperature Mott transition in the Hubbard model with the nearest neighbor hopping on a triangular lattice at half-filling. We estimate the value of the critical interaction to be $U_c=12.0 \\pm 0.5$ in units of the hopping amplitude $t$ through the evolution of the magnetic moment, spectral function, internal energy and specific heat as the interaction $U$ and temperature $T$ ...

Interactions of Ultracold Impurity Particles with Bose-Einstein Condensates

Science.gov (United States)

2015-06-23

AFRL-OSR-VA-TR-2015-0141 INTERACTIONS OF ULTRACOLD IMPURITY PARTICLES WITH BOSE- EINSTEIN CONDENSATES Georg Raithel UNIVERSITY OF MICHIGAN Final...SUBTITLE Interactions of ultracold impurity particles with Bose- Einstein Condensates 5a. CONTRACT NUMBER FA9550-10-1-0453 5b. GRANT NUMBER 5c...Interactions of ultracold impurity particles with Bose- Einstein Condensates Contract/Grant #: FA9550-10-1-0453 Reporting Period: 8/15/2010 to 2/14

Momentum distribution critical exponents for one dimensional large U hubbard model in thermodynamic limit

International Nuclear Information System (INIS)

Qin Shaojin; Yu Lu.

1996-03-01

The critical exponent of the momentum distribution near k F , 3k F and 5k F are studied numerically for one-dimensional U → ∞ Hubbard model, using finite size systems and extrapolating them to the thermodynamic limit. Results at k F agree with earlier calculations, while at 3k F exponents less than 1 are obtained for finite size systems with extrapolation to 1 (regular behaviour) in the thermodynamic limit, in contrast to earlier analytic prediction 9/8. The distribution is regular at 5k F even for finite systems. The singularity near 3k F is interpreted as due to low energy excitations near 3k F in finite systems. (author). 18 refs, 4 figs, 1 tab

Thermalization and Bose-Einstein Condensation in Overpopulated Glasma

International Nuclear Information System (INIS)

Blaizot, Jean-Paul; Gelis, François; Liao, Jinfeng; McLerran, Larry; Venugopalan, Raju

2013-01-01

We report recent progress on understanding the thermalization of the quark-gluon plasma during the early stage in a heavy ion collision. The initially high overpopulation in the far-from-equilibrium gluonic matter (“Glasma”) is shown to play a crucial role. The strongly interacting nature (and thus fast evolution) naturally arises as an emergent property of this pre-equilibrium matter where the intrinsic coupling is weak but the highly occupied gluon states coherently amplify the scattering. A possible transient Bose-Einstein Condensate is argued to form dynamically on a rather general ground. We develop a kinetic approach for describing its evolution toward thermalization as well as the onset of condensation

Thermalization and Bose-Einstein Condensation in Overpopulated Glasma

Energy Technology Data Exchange (ETDEWEB)

Blaizot, Jean-Paul; Gelis, François [Institut de Physique Théorique (URA 2306 du CNRS), CEA/DSM/Saclay, 91191, Gif-sur-Yvette Cedex (France); Liao, Jinfeng [Physics Department and CEEM, Indiana University, 2401 N Milo B. Sampson Lane, Bloomington, IN 47408 (United States); RIKEN BNL Research Center, Bldg. 510A, Brookhaven National Laboratory, Upton, NY 11973 (United States); McLerran, Larry [Physics Department, Bldg. 510A, Brookhaven National Laboratory, Upton, NY 11973 (United States); RIKEN BNL Research Center, Bldg. 510A, Brookhaven National Laboratory, Upton, NY 11973 (United States); Venugopalan, Raju [Physics Department, Bldg. 510A, Brookhaven National Laboratory, Upton, NY 11973 (United States)

2013-05-02

We report recent progress on understanding the thermalization of the quark-gluon plasma during the early stage in a heavy ion collision. The initially high overpopulation in the far-from-equilibrium gluonic matter (“Glasma”) is shown to play a crucial role. The strongly interacting nature (and thus fast evolution) naturally arises as an emergent property of this pre-equilibrium matter where the intrinsic coupling is weak but the highly occupied gluon states coherently amplify the scattering. A possible transient Bose-Einstein Condensate is argued to form dynamically on a rather general ground. We develop a kinetic approach for describing its evolution toward thermalization as well as the onset of condensation.

Readout of the atomtronic quantum interference device

Science.gov (United States)

Haug, Tobias; Tan, Joel; Theng, Mark; Dumke, Rainer; Kwek, Leong-Chuan; Amico, Luigi

2018-01-01

A Bose-Einstein condensate confined in ring shaped lattices interrupted by a weak link and pierced by an effective magnetic flux defines the atomic counterpart of the superconducting quantum interference device: the atomtronic quantum interference device (AQUID). In this paper, we report on the detection of current states in the system through a self-heterodyne protocol. Following the original proposal of the NIST and Paris groups, the ring-condensate many-body wave function interferes with a reference condensate expanding from the center of the ring. We focus on the rf AQUID which realizes effective qubit dynamics. Both the Bose-Hubbard and Gross-Pitaevskii dynamics are studied. For the Bose-Hubbard dynamics, we demonstrate that the self-heterodyne protocol can be applied, but higher-order correlations in the evolution of the interfering condensates are measured to readout of the current states of the system. We study how states with macroscopic quantum coherence can be told apart analyzing the noise in the time of flight of the ring condensate.

Bose-Einstein Condensation

Indian Academy of Sciences (India)

absolute zero. These ideas had ... Everybody is talking about Bose-Einstein condensation. This discovery ... needed if we want to find the probability distribution of the x- ... Boltzmann took two approaches to the problem, both of them deep and ...

High-temperature atomic superfluidity in lattice Bose-Fermi mixtures.

Science.gov (United States)

Illuminati, Fabrizio; Albus, Alexander

2004-08-27

We consider atomic Bose-Fermi mixtures in optical lattices and study the superfluidity of fermionic atoms due to s-wave pairing induced by boson-fermion interactions. We prove that the induced fermion-fermion coupling is always attractive if the boson-boson on-site interaction is repulsive, and predict the existence of an enhanced BEC-BCS crossover as the strength of the lattice potential is varied. We show that for direct on-site fermion-fermion repulsion, the induced attraction can give rise to superfluidity via s-wave pairing at striking variance with the case of pure systems of fermionic atoms with direct repulsive interactions.

High-temperature atomic superfluidity in lattice Bose-Fermi mixtures

International Nuclear Information System (INIS)

Illuminati, Fabrizio; Albus, Alexander

2004-01-01

We consider atomic Bose-Fermi mixtures in optical lattices and study the superfluidity of fermionic atoms due to s-wave pairing induced by boson-fermion interactions. We prove that the induced fermion-fermion coupling is always attractive if the boson-boson on-site interaction is repulsive, and predict the existence of an enhanced BEC-BCS crossover as the strength of the lattice potential is varied. We show that for direct on-site fermion-fermion repulsion, the induced attraction can give rise to superfluidity via s-wave pairing at striking variance with the case of pure systems of fermionic atoms with direct repulsive interactions

Bose-Einstein condensation of paraxial light

OpenAIRE

Klaers, J.; Schmitt, J.; Damm, T.; Vewinger, F.; Weitz, M.

2011-01-01

Photons, due to the virtually vanishing photon-photon interaction, constitute to very good approximation an ideal Bose gas, but owing to the vanishing chemical potential a (free) photon gas does not show Bose-Einstein condensation. However, this is not necessarily true for a lower-dimensional photon gas. By means of a fluorescence induced thermalization process in an optical microcavity one can achieve a thermal photon gas with freely adjustable chemical potential. Experimentally, we have obs...

Fractional statistics and quantum scaling properties of the integrable Penson-Kolb-Hubbard chain

Science.gov (United States)

Vitoriano, Carlindo; Coutinho-Filho, M. D.

2010-09-01

We investigate the ground-state and low-temperature properties of the integrable version of the Penson-Kolb-Hubbard chain. The model obeys fractional statistical properties, which give rise to fractional elementary excitations and manifest differently in the four regions of the phase diagram U/t versus n , where U is the Coulomb coupling, t is the correlated hopping amplitude, and n is the particle density. In fact, we can find local pair formation, fractionalization of the average occupation number per orbital k , or U - and n -dependent average electric charge per orbital k . We also study the scaling behavior near the U -driven quantum phase transitions and characterize their universality classes. Finally, it is shown that in the regime of parameters where local pair formation is energetically more favorable, the ground state exhibits power-law superconductivity; we also stress that above half filling the pair-hopping term stabilizes local Cooper pairs in the repulsive- U regime for U

Charge-spin-orbital dynamics of one-dimensional two-orbital Hubbard model

Energy Technology Data Exchange (ETDEWEB)

Onishi, Hiroaki [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195 (Japan)

2010-01-15

We study the real-time evolution of a charge-excited state in a one-dimensional e{sub g}-orbital degenerate Hubbard model, by a time-dependent density-matrix renormalization group method. Considering a chain along the z direction, electrons hop between adjacent 3z{sup 2}-r{sup 2} orbitals, while x{sup 2}-y{sup 2} orbitals are localized. For the charge-excited state, a holon-doublon pair is introduced into the ground state at quarter filling. At initial time, there is no electron in a holon site, while a pair of electrons occupies 3z{sup 2}-r{sup 2} orbital in a doublon site. As the time evolves, the holon motion is governed by the nearest-neighbor hopping, but the electron pair can transfer between 3z{sup 2}-r{sup 2} orbital and x{sup 2}-y{sup 2} orbital through the pair hopping in addition to the nearest-neighbor hopping. Thus holon and doublon propagate at different speed due to the pair hopping that is characteristic of multi-orbital systems.

Upper limit on the transition temperature for non-ideal Bose gases

International Nuclear Information System (INIS)

Dai Wusheng; Xie Mi

2007-01-01

In this paper, we show that for a non-ideal Bose gas there exists an upper limit on the transition temperature above which Bose-Einstein condensation cannot occur regardless of the pressure applied. Such upper limits for some realistic Bose gases are estimated

Study of Bose-Einstein Correlations in $e^{+}e^{-}\\to W^{+}W^{-}$ events at LEP

CERN Document Server

Abbiendi, G.; Akesson, P.F.; Alexander, G.; Allison, John; Amaral, P.; Anagnostou, G.; Anderson, K.J.; Asai, S.; Axen, D.; Azuelos, G.; Bailey, I.; Barberio, E.; Barillari, T.; Barlow, R.J.; Batley, R.J.; Bechtle, P.; Behnke, T.; Bell, Kenneth Watson; Bell, P.J.; Bella, G.; Bellerive, A.; Benelli, G.; Bethke, S.; Biebel, O.; Boeriu, O.; Bock, P.; Boutemeur, M.; Braibant, S.; Brigliadori, L.; Brown, Robert M.; Buesser, K.; Burckhart, H.J.; Campana, S.; Carnegie, R.K.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, D.G.; Ciocca, C.; Csilling, A.; Cuffiani, M.; Dado, S.; De Roeck, A.; De Wolf, E.A.; Desch, K.; Dienes, B.; Donkers, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Etzion, E.; Fabbri, F.; Feld, L.; Ferrari, P.; Fiedler, F.; Fleck, I.; Ford, M.; Frey, A.; Gagnon, P.; Gary, John William; Gaycken, G.; Geich-Gimbel, C.; Giacomelli, G.; Giacomelli, P.; Giunta, Marina; Goldberg, J.; Gross, E.; Grunhaus, J.; Gruwe, M.; Gunther, P.O.; Gupta, A.; Hajdu, C.; Hamann, M.; Hanson, G.G.; Harel, A.; Hauschild, M.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Herten, G.; Heuer, R.D.; Hill, J.C.; Hoffman, Kara Dion; Horvath, D.; Igo-Kemenes, P.; Ishii, K.; Jeremie, H.; Jovanovic, P.; Junk, T.R.; Kanaya, N.; Kanzaki, J.; Karlen, D.; Kawagoe, K.; Kawamoto, T.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kluth, S.; Klein, K.; Kobayashi, T.; Kobel, M.; Komamiya, S.; Kramer, T.; Kress, T.; Krieger, P.; von Krogh, J.; Kruger, K.; Kuhl, T.; Kupper, M.; Lafferty, G.D.; Landsman, H.; Lanske, D.; Layter, J.G.; Lellouch, D.; Lettso, J.; Levinson, L.; Lillich, J.; Lloyd, S.L.; Loebinger, F.K.; Lu, J.; Ludwig, A.; Ludwig, J.; Mader, W.; Marcellini, S.; Martin, A.J.; Masetti, G.; Mashimo, T.; Mattig, Peter; McKenna, J.; McPherson, R.A.; Meijers, F.; Menges, W.; Merritt, F.S.; Mes, H.; Meyer, Niels T.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Moed, S.; Mohr, W.; Mori, T.; Mutter, A.; Nagai, K.; Nakamura, I.; Nanjo, H.; Neal, H.A.; Nisius, R.; O'Neale, S.W.; Oh, A.; Oreglia, M.J.; Orito, S.; Pahl, C.; Pasztor, G.; Pater, J.R.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poli, B.; Pooth, O.; Przybycien, M.; Quadt, A.; Rabbertz, K.; Rembser, C.; Renkel, P.; Roney, J.M.; Rozen, Y.; Runge, K.; Sachs, K.; Saeki, T.; Sarkisyan, E.K.G.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schieck, J.; Schoerner-Sadenius, Thomas; Schroder, Matthias; Schumacher, M.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Sherwood, P.; Skuja, A.; Smith, A.M.; Sobie, R.; Soldner-Rembold, S.; Spano, F.; Stahl, A.; Strom, David M.; Strohmer, R.; Tarem, S.; Tasevsky, M.; Teuscher, R.; Thomson, M.A.; Torrence, E.; Toya, D.; Tran, P.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turner-Watson, M.F.; Ueda, I.; Ujvari, B.; Vollmer, C.F.; Vannerem, P.; Vertesi, R.; Verzocchi, M.; Voss, H.; Vossebeld, J.; Ward, C.P.; Ward, D.R.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wilson, G.W.; Wilson, J.A.; Wolf, G.; Wyatt, T.R.; Yamashita, S.; Zer-Zion, D.; Zivkovic, Lidija

2004-01-01

Bose-Einstein correlation between like-sign charged-particle pairs in e+e- -> W+W- events recorded with the OPAL detector at LEP at centre-of-mass energies between 183 GeV and 209 GeV are studied. Recently proposed methods which allow direct searches for correlations in the data via distributions of test variables are used to investigate the presence of correlations between hadrons originating from different W bosons in W+W- -> qqqq events. Within the statistics of the data sample no evidence for inter-WW Bose-Einstein correlations is obtained. The data are also compared with predictions of a recent implementation of Bose-Einstein correlation effects in the Monte Carlo model PYTHIA.

Magnetic field dependence of conductivity and effective mass of carriers in a model of Mott-Hubbard material

Directory of Open Access Journals (Sweden)

L.Didukh

2005-01-01

Full Text Available The effect of external magnetic field h on a static conductivity of Mott-Hubbard material which is described by the model with correlated hopping of electrons has been investigated. By means of canonical transformation, the effective Hamiltonian is obtained which takes into account strong intra-site Coulomb repulsion and correlated hopping. Using a variant of generalized Hartree-Fock approximation the single-electron Green function and quasiparticle energy spectrum of the model have been calculated. The static conductivity σ has been calculated as a function of h, electron concentration n and temperature T. The correlated hopping is shown to cause the electron-hole asymmetry of transport properties of narrow band materials.

Low-temperature behaviour of an ideal Bose gas and some forbidden thermodynamic cycles

International Nuclear Information System (INIS)

Chen Jincan; Lin Bihong

2003-01-01

Based on the equation of state of an ideal Bose gas, the heat capacities at constant volume and constant pressure of the Bose system are derived and used to analyse the low-temperature behaviour of the Bose system. It is expounded that some important thermodynamic processes such as a constant pressure and an adiabatic process cannot be carried out from the region of T > T c to that of T c , where T c is the critical temperature of Bose-Einstein condensation of the Bose system. Consequently, some typical thermodynamic cycles such as the Carnot cycle, Brayton cycle, Otto cycle, Ericsson cycle, Diesel cycle and Atkinson cycle cannot be operated across the critical temperature T c of Bose-Einstein condensation of an ideal Bose gas

Two-site Hubbard molecule with a spinless electron-positron pair

KAUST Repository

Cossu, Fabrizio

2012-12-19

We determine the eigenvalues of the two-site Hubbard molecule with one electron and one positron to describe the characteristics of electron-positron interactions in solids. While the effect of hopping is, in general, opposite to the effect of on-site interaction, we find a complex scenario for the electron-positron pair with a non-vanishing potential drop. We give analytical solutions and discuss the combined effects of the model parameters.

Two-site Hubbard molecule with a spinless electron-positron pair

KAUST Repository

Cossu, Fabrizio; Schuster, Cosima; Schwingenschlö gl, Udo

2012-01-01

We determine the eigenvalues of the two-site Hubbard molecule with one electron and one positron to describe the characteristics of electron-positron interactions in solids. While the effect of hopping is, in general, opposite to the effect of on-site interaction, we find a complex scenario for the electron-positron pair with a non-vanishing potential drop. We give analytical solutions and discuss the combined effects of the model parameters.

Entanglement dynamics following a sudden quench: An exact solution

Science.gov (United States)

Ghosh, Supriyo; Gupta, Kumar S.; Srivastava, Shashi C. L.

2017-12-01

We present an exact and fully analytical treatment of the entanglement dynamics for an isolated system of N coupled oscillators following a sudden quench of the system parameters. The system is analyzed using the solutions of the time-dependent Schrodinger's equation, which are obtained by solving the corresponding nonlinear Ermakov equations. The entanglement entropies exhibit a multi-oscillatory behaviour, where the number of dynamically generated time scales increases with N. The harmonic chains exhibit entanglement revival and for larger values of N (> 10), we find near-critical logarithmic scaling for the entanglement entropy, which is modulated by a time-dependent factor. The N = 2 case is equivalent to the two-site Bose-Hubbard model in the tunneling regime, which is amenable to empirical realization in cold-atom systems.

Ground-state properties of anyons in a one-dimensional lattice

Science.gov (United States)

Tang, Guixin; Eggert, Sebastian; Pelster, Axel

2015-12-01

Using the Anyon-Hubbard Hamiltonian, we analyze the ground-state properties of anyons in a one-dimensional lattice. To this end we map the hopping dynamics of correlated anyons to an occupation-dependent hopping Bose-Hubbard model using the fractional Jordan-Wigner transformation. In particular, we calculate the quasi-momentum distribution of anyons, which interpolates between Bose-Einstein and Fermi-Dirac statistics. Analytically, we apply a modified Gutzwiller mean-field approach, which goes beyond a classical one by including the influence of the fractional phase of anyons within the many-body wavefunction. Numerically, we use the density-matrix renormalization group by relying on the ansatz of matrix product states. As a result it turns out that the anyonic quasi-momentum distribution reveals both a peak-shift and an asymmetry which mainly originates from the nonlocal string property. In addition, we determine the corresponding quasi-momentum distribution of the Jordan-Wigner transformed bosons, where, in contrast to the hard-core case, we also observe an asymmetry for the soft-core case, which strongly depends on the particle number density.

Study related to the generation of the conditional intensities of ideal Bose-gas

International Nuclear Information System (INIS)

Al-Oklah, H.

2007-01-01

In this paper, we will answer on the following question: Are there any conditions on the chemical potential and temperature of an ideal BOSE gas when generating the conditional intensities of ideal Bose-gas, and will the position distribution of the ideal Bose-gas be a Gibbs-process. The study shows that there should be no conditions on the chemical potential and thermodynamical temperature of an ideal BOSE gas when we generate the conditional intensities of ideal Bose-gas except that the fundamental conditions, the chemical potential is negative and the inverse temperature is positive. Thus the position distribution of the ideal Bose-gas may only be a Gibbs-process, in the special case when the thermodynamical temperature of the ideal BOSE gas tends to the absolute zero. (author)

Bose, Prof. Arup

Indian Academy of Sciences (India)

Home; Fellowship. Fellow Profile. Elected: 2006 Section: Mathematical Sciences. Bose, Prof. Arup Ph.D. (ISI, Calcutta), FNA, FNASc. Date of birth: 1 April 1959. Specialization: Probability and Statistics, Economics Address: Professor, Statistics & Mathematics Unit, Indian Statistical Institute, 203, B.T. Road, Kolkata 700 108, ...

Coupled dynamics of interacting spin-1 bosons in a double-well potential

Science.gov (United States)

Carvalho, D. W. S.; Foerster, A.; Gusmão, M. A.

2018-03-01

We present a detailed analysis of dynamical processes involving two or three particles in a double-well potential. Motivated by experimental realizations of such a system with optically trapped cold atoms, we focus on spin-1 bosons with special attention on the effects of a spin-dependent interaction in addition to the usual Hubbard-like repulsive one. For a sufficiently weak tunneling amplitude in comparison to the dominant Hubbard coupling, particle motion is strongly correlated, occurring only under fine-tuned relationships between well-depth asymmetry and interactions. We highlight processes involving tunneling of coupled particle pairs and triads, emphasizing the role of the spin-dependent interaction in resonance conditions.

Fluctuation-induced forces in confined ideal and imperfect Bose gases.

Science.gov (United States)

Diehl, H W; Rutkevich, Sergei B

2017-06-01

Fluctuation-induced ("Casimir") forces caused by thermal and quantum fluctuations are investigated for ideal and imperfect Bose gases confined to d-dimensional films of size ∞^{d-1}×D under periodic (P), antiperiodic (A), Dirichlet-Dirichlet (DD), Neumann-Neumann (NN), and Robin (R) boundary conditions (BCs). The full scaling functions Υ_{d}^{BC}(x_{λ}=D/λ_{th},x_{ξ}=D/ξ) of the residual reduced grand potential per area φ_{res,d}^{BC}(T,μ,D)=D^{-(d-1)}Υ_{d}^{BC}(x_{λ},x_{ξ}) are determined for the ideal gas case with these BCs, where λ_{th} and ξ are the thermal de Broglie wavelength and the bulk correlation length, respectively. The associated limiting scaling functions Θ_{d}^{BC}(x_{ξ})≡Υ_{d}^{BC}(∞,x_{ξ}) describing the critical behavior at the bulk condensation transition are shown to agree with those previously determined from a massive free O(2) theory for BC=P,A,DD,DN,NN. For d=3, they are expressed in closed analytical form in terms of polylogarithms. The analogous scaling functions Υ_{d}^{BC}(x_{λ},x_{ξ},c_{1}D,c_{2}D) and Θ_{d}^{R}(x_{ξ},c_{1}D,c_{2}D) under the RBCs (∂_{z}-c_{1})ϕ|_{z=0}=(∂_{z}+c_{2})ϕ|_{z=D}=0 with c_{1}≥0 and c_{2}≥0 are also determined. The corresponding scaling functions Υ_{∞,d}^{P}(x_{λ},x_{ξ}) and Θ_{∞,d}^{P}(x_{ξ}) for the imperfect Bose gas are shown to agree with those of the interacting Bose gas with n internal degrees of freedom in the limit n→∞. Hence, for d=3, Θ_{∞,d}^{P}(x_{ξ}) is known exactly in closed analytic form. To account for the breakdown of translation invariance in the direction perpendicular to the boundary planes implied by free BCs such as DDBCs, a modified imperfect Bose gas model is introduced that corresponds to the limit n→∞ of this interacting Bose gas. Numerically and analytically exact results for the scaling function Θ_{∞,3}^{DD}(x_{ξ}) therefore follow from those of the O(2n)ϕ^{4} model for n→∞.

Similarities between the Hubbard and Periodic Anderson Models at Finite Temperatures

International Nuclear Information System (INIS)

Held, K.; Huscroft, C.; Scalettar, R. T.; McMahan, A. K.

2000-01-01

The single band Hubbard and the two band periodic Anderson Hamiltonians have traditionally been applied to rather different physical problems--the Mott transition and itinerant magnetism, and Kondo singlet formation and scattering off localized magnetic states, respectively. In this paper, we compare the magnetic and charge correlations, and spectral functions, of the two systems. We show quantitatively that they exhibit remarkably similar behavior, including a nearly identical topology of the finite temperature phase diagrams at half filling. We address potential implications of this for theories of the rare earth ''volume collapse'' transition. (c) 2000 The American Physical Society

Study of Bose-Einstein correlations in e+e-→W+W- events at LEP

International Nuclear Information System (INIS)

Abbiendi, G.; Aimsley, C.; Aakesson, C.

2004-01-01

Bose-Einstein correlations between like-sign charged-particle pairs in e + e - →W + W - events recorded with the OPAL detector at LEP at centre-of-mass energies between 183 GeV and 209 GeV are studied. Recently proposed methods which allow direct searches for correlations in the data via distributions of test variables are used to investigate the presence of correlations between hadrons originating from different W bosons in W + W - →q anti qq anti q events. Within the statistics of the data sample no evidence for inter-WW Bose-Einstein correlations is obtained. The data are also compared with predictions of a recent implementation of Bose-Einstein correlation effects in the Monte Carlo model PYTHIA. (orig.)

The Mott transition in the strong coupling perturbation theory

International Nuclear Information System (INIS)

Sherman, A.

2015-01-01

Using the strong coupling diagram technique a self-consistent equation for the electron Green's function is derived for the repulsive Hubbard model. Terms of two lowest orders of the ratio of the bandwidth Δ to the Hubbard repulsion U are taken into account in the irreducible part of the Larkin equation. The obtained equation is shown to retain causality and reduces to Green's function of uncorrelated electrons in the limit U→0. Calculations were performed for the semi-elliptical initial band. It is shown that the approximation describes the Mott transition, which occurs at U c =√(3)Δ/2. This value coincides with that obtained in the Hubbard-III approximation. At half-filling, for 0U c the Mott gap disappears

Bose-Einstein Condensation in Complex Networks

International Nuclear Information System (INIS)

Bianconi, Ginestra; Barabasi, Albert-Laszlo

2001-01-01

The evolution of many complex systems, including the World Wide Web, business, and citation networks, is encoded in the dynamic web describing the interactions between the system's constituents. Despite their irreversible and nonequilibrium nature these networks follow Bose statistics and can undergo Bose-Einstein condensation. Addressing the dynamical properties of these nonequilibrium systems within the framework of equilibrium quantum gases predicts that the 'first-mover-advantage,' 'fit-get-rich,' and 'winner-takes-all' phenomena observed in competitive systems are thermodynamically distinct phases of the underlying evolving networks

Discrete Bose-Einstein spectra

International Nuclear Information System (INIS)

Vlad, Valentin I.; Ionescu-Pallas, Nicholas

2001-03-01

The Bose-Einstein energy spectrum of a quantum gas, confined in a rigid cubic box, is shown to become discrete and strongly dependent on the box geometry (size L), temperature, T and atomic mass number, A at , in the region of small γ=A at TV 1/3 . This behavior is the consequence of the random state degeneracy in the box. Furthermore, we demonstrate that the total energy does not obey the conventional law any longer, but a new law, which depends on γ and on the quantum gas fugacity. This energy law imposes a faster decrease to zero than it is classically expected, for γ→0. The lighter the gas atoms, the higher the temperatures or the box size, for the same effects in the discrete Bose-Einstein regime. (author)

Atomic Quantum Simulations of Abelian and non-Abelian Gauge Theories

CERN Multimedia

CERN. Geneva

2014-01-01

Using a Fermi-Bose mixture of ultra-cold atoms in an optical lattice, in a collaboration of atomic and particle physicists, we have constructed a quantum simulator for a U(1) gauge theory coupled to fermionic matter. The construction is based on quantum link models which realize continuous gauge symmetry with discrete quantum variables. At low energies, quantum link models with staggered fermions emerge from a Hubbard-type model which can be quantum simulated. This allows investigations of string breaking as well as the real-time evolution after a quench in gauge theories, which are inaccessible to classical simulation methods. Similarly, using ultracold alkaline-earth atoms in optical lattices, we have constructed a quantum simulator for U(N) and SU(N) lattice gauge theories with fermionic matter based on quantum link models. These systems share qualitative features with QCD, including chiral symmetry breaking and restoration at non-zero temperature or baryon density. Unlike classical simulations, a quantum ...

Dynamics of a strongly driven two-component Bose-Einstein condensate

International Nuclear Information System (INIS)

Salmond, G.L.; Holmes, C.A.; Milburn, G.J.

2002-01-01

We consider a two-component Bose-Einstein condensate in two spatially localized modes of a double-well potential, with periodic modulation of the tunnel coupling between the two modes. We treat the driven quantum field using a two-mode expansion and define the quantum dynamics in terms of the Floquet Operator for the time periodic Hamiltonian of the system. It has been shown that the corresponding semiclassical mean-field dynamics can exhibit regions of regular and chaotic motion. We show here that the quantum dynamics can exhibit dynamical tunneling between regions of regular motion, centered on fixed points (resonances) of the semiclassical dynamics

Quantum ratchets for periodically kicked cold atoms and Bose-Einstein condensates

Energy Technology Data Exchange (ETDEWEB)

Casati, Giulio [Center for Nonlinear and Complex Systems, Universita degli Studi dell' Insubria and Istituto Nazionale per la Fisica della Materia, Unita di Como, Via Valleggio 11, 22100 Como (Italy); Poletti, Dario [Center for Nonlinear and Complex Systems, Universita degli Studi dell' Insubria and Istituto Nazionale per la Fisica della Materia, Unita di Como, Via Valleggio 11, 22100 Como (Italy)

2007-05-15

We study cold atoms and Bose-Einstein condensates exposed to time-dependent standing waves of light. We first discuss a quantum chaotic dissipative ratchet using the method of quantum trajectories. This system is characterized by directed transport emerging from a quantum strange attractor. We then present a very simple model of directed transport with cold atoms in a pair of periodically flashed optical lattices. Finally we study the dynamics of a dilute Bose-Einstein condensate confined in a toroidal trap and exposed to a pair of periodically flashed optical lattices. We show that the many-body atom-atom interactions, treated within the mean-field approximation, can generate directed transport.

Investigation of Bose Condensation in Ideal Bose Gas Trapped under Generic Power Law Potential in d Dimension

Science.gov (United States)

Mehedi Faruk, Mir; Sazzad Hossain, Md.; Muktadir Rahman, Md.

2016-02-01

The changes in characteristics of Bose condensation of ideal Bose gas due to an external generic power law potential U=\\sumi=1dci\\vert xi/ai\\vertni are studied carefully. Detailed calculation of Kim et al. (J. Phys. Condens. Matter 11 (1999) 10269) yielded the hierarchy of condensation transitions with changing fractional dimensionality. In this manuscript, some theorems regarding specific heat at constant volume CV are presented. Careful examination of these theorems reveal the existence of hidden hierarchy of the condensation transition in trapped systems as well.

Variational study of the stability of the Nagaoka state against single-spin flips in the two-dimensional t-t#prime# Hubbard model

International Nuclear Information System (INIS)

Bajdich, M.; Hlubina, R.

2001-01-01

Making use of variational wave functions of the Basile-Elser type we study the stability of the Nagaoka state against single-spin flips in the two-dimensional t-t#prime# Hubbard model for t#prime#/t∼0.5. In the low-density limit the variational estimate of the stability region of the Nagaoka state is in qualitative agreement with the predictions of the T-matrix approximation

Fermi-liquid to non-Fermi-liquid transition in a dynamical generalization of the CPA in a disordered Hubbard model

International Nuclear Information System (INIS)

Dasgupta, I.; Mookerjee, A.

1993-07-01

Based on the Augmented Space formalism proposed by one of us and a generalization of the alloy analogy, including the effect of the dynamics of the exchange bath, we show that a half-filled Hubbard model shows Fermi-liquid behaviour at low values of the interaction parameter U. This gives way to non-Fermi liquid behaviour at a critical U, where the system is still metallic. We also show that quenched disorder tends to lower this critical value of U. (author). 19 refs, 2 figs

Magnetic impurity coupled to interacting conduction electrons

International Nuclear Information System (INIS)

Schork, T.

1996-01-01

We consider a magnetic impurity which interacts by hybridization with a system of weakly correlated electrons and determine the energy of the ground state by means of a 1/N f expansion. The correlations among the conduction electrons are described by a Hubbard Hamiltonian and are treated to the lowest order in the interaction strength. We find that their effect on the Kondo temperature, T K , in the Kondo limit is twofold: first, the position of the impurity level is shifted due to the reduction of charge fluctuations, which reduces T K . Secondly, the bare Kondo exchange coupling is enhanced as spin fluctuations are enlarged. In total, T K increases. Both corrections require intermediate states beyond the standard Varma-Yafet ansatz. This shows that the Hubbard interaction does not just provide quasiparticles, which hybridize with the impurity, but also renormalizes the Kondo coupling. copyright 1996 The American Physical Society

Generation of atom-photon entangled states in atomic Bose-Einstein condensate via electromagnetically induced transparency

International Nuclear Information System (INIS)

Kuang Leman; Zhou Lan

2003-01-01

In this paper, we present a method to generate continuous-variable-type entangled states between photons and atoms in atomic Bose-Einstein condensate (BEC). The proposed method involves an atomic BEC with three internal states, a weak quantized probe laser, and a strong classical coupling laser, which form a three-level Λ-shaped BEC system. We consider a situation where the BEC is in electromagnetically induced transparency with the coupling laser being much stronger than the probe laser. In this case, the upper and intermediate levels are unpopulated, so that their adiabatic elimination enables an effective two-mode model involving only the atomic field at the lowest internal level and the quantized probe laser field. Atom-photon quantum entanglement is created through laser-atom and interatomic interactions, and two-photon detuning. We show how to generate atom-photon entangled coherent states and entangled states between photon (atom) coherent states and atom-(photon-) macroscopic quantum superposition (MQS) states, and between photon-MQS and atom-MQS states

Projected coupled cluster theory.

Science.gov (United States)

Qiu, Yiheng; Henderson, Thomas M; Zhao, Jinmo; Scuseria, Gustavo E

2017-08-14

Coupled cluster theory is the method of choice for weakly correlated systems. But in the strongly correlated regime, it faces a symmetry dilemma, where it either completely fails to describe the system or has to artificially break certain symmetries. On the other hand, projected Hartree-Fock theory captures the essential physics of many kinds of strong correlations via symmetry breaking and restoration. In this work, we combine and try to retain the merits of these two methods by applying symmetry projection to broken symmetry coupled cluster wave functions. The non-orthogonal nature of states resulting from the application of symmetry projection operators furnishes particle-hole excitations to all orders, thus creating an obstacle for the exact evaluation of overlaps. Here we provide a solution via a disentanglement framework theory that can be approximated rigorously and systematically. Results of projected coupled cluster theory are presented for molecules and the Hubbard model, showing that spin projection significantly improves unrestricted coupled cluster theory while restoring good quantum numbers. The energy of projected coupled cluster theory reduces to the unprojected one in the thermodynamic limit, albeit at a much slower rate than projected Hartree-Fock.

Optical absorption in a degenerate Bose-Einstein gas

International Nuclear Information System (INIS)

Yip, S.K.

2002-01-01

We develop a theory on optical absorption in a dilute Bose-Einstein gas at low temperatures. This theory is motivated by the Bogoliubov theory of elementary excitations for this system, and takes into account explicitly the modification of the nature and dispersion of elementary excitations due to Bose-Einstein condensation. Our results show important differences from existing theories

Pseudogap and Fermi-Surface Topology in the Two-Dimensional Hubbard Model

Science.gov (United States)

Wu, Wei; Scheurer, Mathias S.; Chatterjee, Shubhayu; Sachdev, Subir; Georges, Antoine; Ferrero, Michel

2018-04-01

One of the distinctive features of hole-doped cuprate superconductors is the onset of a "pseudogap" below a temperature T* . Recent experiments suggest that there may be a connection between the existence of the pseudogap and the topology of the Fermi surface. Here, we address this issue by studying the two-dimensional Hubbard model with two distinct numerical methods. We find that the pseudogap only exists when the Fermi surface is holelike and that, for a broad range of parameters, its opening is concomitant with a Fermi-surface topology change from electronlike to holelike. We identify a common link between these observations: The polelike feature of the electronic self-energy associated with the formation of the pseudogap is found to also control the degree of particle-hole asymmetry, and hence the Fermi-surface topology transition. We interpret our results in the framework of an SU(2) gauge theory of fluctuating antiferromagnetism. We show that a mean-field treatment of this theory in a metallic state with U(1) topological order provides an explanation of this polelike feature and a good description of our numerical results. We discuss the relevance of our results to experiments on cuprates.

Shrinking of a condensed fermionic cloud in a trap approaching the Bose-Einstein condensation limit

International Nuclear Information System (INIS)

Perali, A.; Pieri, P.; Strinati, G. C.

2003-01-01

We determine the zero-temperature density profile of a cloud of fermionic atoms in a trap subject to a mutual attractive interaction, as the strength of the interaction is progressively increased. We find a significant decrease of the size of the atomic cloud as it evolves from the weak-coupling regime of overlapping Cooper pairs to the strong-coupling (Bose-Einstein) regime of nonoverlapping bound-fermion pairs. Most significantly, we find a pronounced increase of the value of the density at the center of the trap (even by an order of magnitude) when evolving between the two regimes. Our results are based on a generalized Thomas-Fermi approximation for the superfluid state, which covers continuously all coupling regimes

Calculation of thermodynamic properties of finite Bose-Einstein systems

NARCIS (Netherlands)

Borrmann, P.; Harting, J.D.R.; Mülken, O.; Hilf, E.

1999-01-01

We derive an exact recursion formula for the calculation of thermodynamic functions of finite systems obeying Bose-Einstein statistics. The formula is applicable for canonical systems where the particles can be treated as noninteracting in some approximation, e.g., like Bose-Einstein condensates in

Comparative DMFT study of the eg-orbital Hubbard model in thin films

Science.gov (United States)

Rüegg, Andreas; Hung, Hsiang-Hsuan; Gull, Emanuel; Fiete, Gregory A.

2014-02-01

Heterostructures of transition-metal oxides have emerged as a new route to engineer electronic systems with desired functionalities. Motivated by these developments, we study a two-orbital Hubbard model in a thin-film geometry confined along the cubic [001] direction using the dynamical mean-field theory. We contrast the results of two approximate impurity solvers (exact diagonalization and one-crossing approximation) to the results of the numerically exact continuous-time quantum Monte Carlo solver. Consistent with earlier studies, we find that the one-crossing approximation performs well in the insulating regime, while the advantage of the exact-diagonalization-based solver is more pronounced in the metallic regime. We then investigate various aspects of strongly correlated eg-orbital systems in thin-film geometries. In particular, we show how the interfacial orbital polarization dies off quickly a few layers from the interface and how the film thickness affects the location of the interaction-driven Mott transition. In addition, we explore the changes in the electronic structure with varying carrier concentration and identify large variations of the orbital polarization in the strongly correlated regime.

Interaction effects on dynamic correlations in noncondensed Bose gases

NARCIS (Netherlands)

Bezett, A.; Van Driel, H. J.; Mink, M. P.; Stoof, H. T C; Duine, R. A.

2014-01-01

We consider dynamic, i.e., frequency-dependent, correlations in noncondensed ultracold atomic Bose gases. In particular, we consider the single-particle correlation function and its power spectrum. We compute this power spectrum for a one-component Bose gas, and we show how it depends on the

Using the Model Coupling Toolkit to couple earth system models

Science.gov (United States)

Warner, J.C.; Perlin, N.; Skyllingstad, E.D.

2008-01-01

Continued advances in computational resources are providing the opportunity to operate more sophisticated numerical models. Additionally, there is an increasing demand for multidisciplinary studies that include interactions between different physical processes. Therefore there is a strong desire to develop coupled modeling systems that utilize existing models and allow efficient data exchange and model control. The basic system would entail model "1" running on "M" processors and model "2" running on "N" processors, with efficient exchange of model fields at predetermined synchronization intervals. Here we demonstrate two coupled systems: the coupling of the ocean circulation model Regional Ocean Modeling System (ROMS) to the surface wave model Simulating WAves Nearshore (SWAN), and the coupling of ROMS to the atmospheric model Coupled Ocean Atmosphere Prediction System (COAMPS). Both coupled systems use the Model Coupling Toolkit (MCT) as a mechanism for operation control and inter-model distributed memory transfer of model variables. In this paper we describe requirements and other options for model coupling, explain the MCT library, ROMS, SWAN and COAMPS models, methods for grid decomposition and sparse matrix interpolation, and provide an example from each coupled system. Methods presented in this paper are clearly applicable for coupling of other types of models. ?? 2008 Elsevier Ltd. All rights reserved.

Dynamics of fermionic Hubbard models after interaction quenches in one and two dimensions

International Nuclear Information System (INIS)

Hamerla, Simone Anke

2013-10-01

In the last years the impressive progress on the experimental side led to a variety of new experiments allowing to address systems out of equilibrium. In this way the behavior of such systems far from equilibrium is no longer a purely theoretical issue but indeed observable. New experimental techniques, like particles trapped in optical lattices, render a realization of quantum systems with nearly arbitrary system parameters possible and provide a possibility to study their time evolution. Systems out of equilibrium are characterized by the fact, that these systems are in highly excited states giving rise to totally new fascinating properties. In the present thesis one- and two-dimensional fermionic Hubbard models out of equilibrium are discussed. The system is taken out of equilibrium by a so-called interaction quench. At the beginning the system is prepared in the groundstate of the non-interacting Hamiltonian. At a time t the interaction between the fermions is suddenly turned on so that the time evolution is governed by the whole, interacting Hamiltonian. Hence the system is prepared in the groundstate of one Hamiltonian but evolves according to a different Hamiltonian. Consequently the system ends up in a highly excited state. To describe such a system a method based on an expansion of the Heisenberg equations of motion to highest order possible is developed in this thesis. This method provides an exact description of the time evolution on short and intermediate time scales after the quench. As the method reveal exact results and does not rely on any perturbative assumption, a study of arbitrarily large interaction strengths is possible. Besides, the method is one of the few methods capable of two-dimensional systems. In the following the method used in this thesis is explained and advantages and disadvantages of the approach are thematized. For this purpose the results of the developed iterated equation of motion approach are compared to results obtained in

Dynamics of fermionic Hubbard models after interaction quenches in one and two dimensions

Energy Technology Data Exchange (ETDEWEB)

Hamerla, Simone Anke

2013-10-15

In the last years the impressive progress on the experimental side led to a variety of new experiments allowing to address systems out of equilibrium. In this way the behavior of such systems far from equilibrium is no longer a purely theoretical issue but indeed observable. New experimental techniques, like particles trapped in optical lattices, render a realization of quantum systems with nearly arbitrary system parameters possible and provide a possibility to study their time evolution. Systems out of equilibrium are characterized by the fact, that these systems are in highly excited states giving rise to totally new fascinating properties. In the present thesis one- and two-dimensional fermionic Hubbard models out of equilibrium are discussed. The system is taken out of equilibrium by a so-called interaction quench. At the beginning the system is prepared in the groundstate of the non-interacting Hamiltonian. At a time t the interaction between the fermions is suddenly turned on so that the time evolution is governed by the whole, interacting Hamiltonian. Hence the system is prepared in the groundstate of one Hamiltonian but evolves according to a different Hamiltonian. Consequently the system ends up in a highly excited state. To describe such a system a method based on an expansion of the Heisenberg equations of motion to highest order possible is developed in this thesis. This method provides an exact description of the time evolution on short and intermediate time scales after the quench. As the method reveal exact results and does not rely on any perturbative assumption, a study of arbitrarily large interaction strengths is possible. Besides, the method is one of the few methods capable of two-dimensional systems. In the following the method used in this thesis is explained and advantages and disadvantages of the approach are thematized. For this purpose the results of the developed iterated equation of motion approach are compared to results obtained in

Field-induced phase transition in a metalorganic spin-dimer system-a potential model system to study Bose-Einstein condensation of magnons

International Nuclear Information System (INIS)

Tsui, Y.; Bruehl, A.; Removic-Langer, K.; Pashchenko, V.; Wolf, B.; Donath, G.; Pikul, A.; Kretz, T.; Lerner, H.-W.; Wagner, M.; Salguero, A.; Saha-Dasgupta, T.; Rahaman, B.; Valenti, R.; Lang, M.

2007-01-01

We report on the results obtained from studying electron spin resonance, magnetic susceptibility, specific heat and thermal expansion experiments on a metalorganic spin-dimer system, C 36 H 48 Cu 2 F 6 N 8 O 12 S 2 (TK91). According to the first principle Density Functional Theory calculations, the compound represents a 3D-coupled dimer system with intradimer coupling J 1 /k B ∼ 10K and interdimer couplings J 2 /k B ∼J 3 /k B ∼ 1K. The measurements have been performed on both pressed powder and single-crystal samples in external magnetic fields up to 12T and at low temperatures down to ∼ 0.2K. Susceptibility measurements reveal a spin-gap behavior consistent with the theoretical results. Furthermore, clear indications of a field-induced phase transition have been observed. A similar field-induced phase transition was also detected in an inorganic compound TlCuCl 3 and was interpreted as Bose-Einstein condensation (BEC) of magnons. The possibility of changing both the intradimer and interdimer couplings in TK91 by chemical substitutions makes the system a potentially good system to study BEC of magnons

Energies and damping rates of elementary excitations in spin-1 Bose-Einstein-condensed gases

International Nuclear Information System (INIS)

Szirmai, Gergely; Szepfalusy, Peter; Kis-Szabo, Krisztian

2003-01-01

The finite temperature Green's function technique is used to calculate the energies and damping rates of the elementary excitations of homogeneous, dilute, spin-1 Bose gases below the Bose-Einstein condensation temperature in both the density and spin channels. For this purpose a self-consistent dynamical Hartree-Fock model is formulated, which takes into account the direct and exchange processes on equal footing by summing up certain classes of Feynman diagrams. The model is shown to satisfy the Goldstone theorem and to exhibit the hybridization of one-particle and collective excitations correctly. The results are applied to gases of 23 Na and 87 Rb atoms

Fluctuation-induced forces in confined ideal and imperfect Bose gases

Science.gov (United States)

Diehl, H. W.; Rutkevich, Sergei B.

2017-06-01

Fluctuation-induced ("Casimir") forces caused by thermal and quantum fluctuations are investigated for ideal and imperfect Bose gases confined to d -dimensional films of size ∞d -1×D under periodic (P), antiperiodic (A), Dirichlet-Dirichlet (DD), Neumann-Neumann (NN), and Robin (R) boundary conditions (BCs). The full scaling functions ΥdBC(xλ=D /λth ,xξ=D /ξ ) of the residual reduced grand potential per area φres,dBC(T ,μ ,D ) =D-(d -1 )ΥdBC(xλ,xξ) are determined for the ideal gas case with these BCs, where λth and ξ are the thermal de Broglie wavelength and the bulk correlation length, respectively. The associated limiting scaling functions ΘdBC(xξ) ≡ΥdBC(∞ ,xξ) describing the critical behavior at the bulk condensation transition are shown to agree with those previously determined from a massive free O (2 ) theory for BC=P,A,DD,DN,NN . For d =3 , they are expressed in closed analytical form in terms of polylogarithms. The analogous scaling functions ΥdBC(xλ,xξ,c1D ,c2D ) and ΘdR(xξ,c1D ,c2D ) under the RBCs (∂z-c1) ϕ |z=0=(∂z+c2) ϕ | z =D=0 with c1≥0 and c2≥0 are also determined. The corresponding scaling functions Υ∞,d P(xλ,xξ) and Θ∞,d P(xξ) for the imperfect Bose gas are shown to agree with those of the interacting Bose gas with n internal degrees of freedom in the limit n →∞ . Hence, for d =3 , Θ∞,d P(xξ) is known exactly in closed analytic form. To account for the breakdown of translation invariance in the direction perpendicular to the boundary planes implied by free BCs such as DDBCs, a modified imperfect Bose gas model is introduced that corresponds to the limit n →∞ of this interacting Bose gas. Numerically and analytically exact results for the scaling function Θ∞,3 DD(xξ) therefore follow from those of the O (2 n ) ϕ4 model for n →∞ .

Decay of superfluid currents in the interacting one-dimensional Bose gas

International Nuclear Information System (INIS)

Cherny, Alexander Yu.; Caux, Jean-Sebastien; Brand, Joachim

2009-01-01

We examine the superfluid properties of a one-dimensional (1D) Bose gas in a ring trap based on the model of Lieb and Liniger. While the 1D Bose gas has nonclassical rotational inertia and exhibits quantization of velocities, the metastability of currents depends sensitively on the strength of interactions in the gas: the stronger the interactions, the faster the current decays. It is shown that the Landau critical velocity is zero in the thermodynamic limit due to the first supercurrent state, which has zero energy and finite probability of excitation. We calculate the energy dissipation rate of ring currents in the presence of weak defects, which should be observable on experimental time scales.

Interference of an array of independent Bose-Einstein condensates

International Nuclear Information System (INIS)

Hadzibabic, Zoran; Stock, Sabine; Battelier, Baptiste; Bretin, Vincent; Dalibard, Jean

2004-01-01

We have observed high-contrast matter wave interference between 30 Bose-Einstein condensates with uncorrelated phases. Interferences were observed after the independent condensates were released from a one-dimensional optical lattice and allowed to overlap. This phenomenon is explained with a simple theoretical model, which generalizes the analysis of the interference of two condensates

Hubbard U calculations for gap states in dilute magnetic semiconductors.

Science.gov (United States)

Fukushima, T; Katayama-Yoshida, H; Sato, K; Bihlmayer, G; Mavropoulos, P; Bauer, D S G; Zeller, R; Dederichs, P H

2014-07-09

On the basis of constrained density functional theory, we present ab initio calculations for the Hubbard U parameter of transition metal impurities in dilute magnetic semiconductors, choosing Mn in GaN as an example. The calculations are performed by two methods: (i) the Korringa-Kohn-Rostoker (KKR) Green function method for a single Mn impurity in GaN and (ii) the full-potential linearized augmented plane-wave (FLAPW) method for a large supercell of GaN with a single Mn impurity in each cell. By changing the occupancy of the majority t2 gap state of Mn, we determine the U parameter either from the total energy differences E(N + 1) and E(N - 1) of the (N ± 1)-electron excited states with respect to the ground state energy E(N), or by using the single-particle energies for n(0) ± 1/2 occupancies around the charge-neutral occupancy n0 (Janak's transition state model). The two methods give nearly identical results. Moreover the values calculated by the supercell method agree quite well with the Green function values. We point out an important difference between the 'global' U parameter calculated using Janak's theorem and the 'local' U of the Hubbard model.

Generalized hyperbolic functions to find soliton-like solutions for a system of coupled nonlinear Schroedinger equations

International Nuclear Information System (INIS)

Yomba, Emmanuel

2008-01-01

With the aid of symbolic computation, we demonstrate that the known method which is based on the new generalized hyperbolic functions and the new kinds of generalized hyperbolic function transformations, generates classes of exact solutions to a system of coupled nonlinear Schroedinger equations. This system includes the modified Hubbard model and the system of coupled nonlinear Schroedinger derived by Lazarides and Tsironis. Four types of solutions for this system are given explicitly, namely: new bright-bright, new dark-dark, new bright-dark and new dark-bright solitons

Bose-Einstein correlations

International Nuclear Information System (INIS)

Zalewski, Kacper

2000-01-01

The effect of Bose-Einstein correlations on multiplicity distributions of identical pions is discussed. It is found that these correlations affect significantly the observed multiplicity distributions, but Einstein's condensation is unlikely to be achieved, unless 'cold spots', i.e. regions, where groups of pions with very small relative momenta are produced, occur in high energy heavy-ion collisions

Coherent tunneling of Bose-Einstein condensates: Exact solutions for Josephson effects and macroscopic quantum self-trapping

International Nuclear Information System (INIS)

Raghavan, S.; Fantoni, S.; Shenoy, S.R.; Smerzi, A.

1997-07-01

We consider coherent atomic tunneling between two weakly coupled Bose-Einstein condensates (BEC) at T = 0 in (possibly asymmetric) double-well trap. The condensate dynamics of the macroscopic amplitudes in the two wells is modeled by two Gross-Pitaevskii equations (GPE) coupled by a tunneling matrix element. The evolution of the inter-well fractional population imbalance (related to the condensate phase difference) is obtained in terms of elliptic functions, generalizing well-known Josephson effects such as the 'ac' effect, the 'plasma oscillations', and the resonant Shapiro effect, to the nonsiusoidal regimes. We also present exact solutions for a novel 'macroscopic quantum self-trapping' effect arising from nonlinear atomic self-interaction in the GPE. The coherent BEC tunneling signatures are obtained in terms of the oscillations periods and the Fourier spectrum of the imbalance oscillations, as a function of the initial values of GPE parameters. Experimental procedures are suggested to make contact with theoretical predictions. (author). 44 refs, 8 figs

Numerical methods for strongly correlated many-body systems with bosonic degrees of freedom

International Nuclear Information System (INIS)

Dorfner, Florian Guenter

2017-01-01

dimension also during time evolution. For the polaron problem on an infinite chain Krylov-space time evolution in a limited functional space has been shown to be very efficient. We adapt this algorithm to periodic boundary conditions and show that it is the most efficient method compared to standard Krylov space time evolution and the time-evolving block decimation method. We also study the properties of the local reduced density matrix as a function of model parameters and under non-equilibrium conditions in three different models: the Bose-Bose resonance model, the Holstein model and the Hubbard-Holstein model. It was shown for fermionic and spin models that the single-site von Neumann entropy is an indicator for phase transitions. In the Bose-Bose resonance model we find that both, the local von Neumann entropy and the eigenstates of the local reduced density matrix show features in the vicinity of a phase boundary. Also, we find that the eigenstates of the local reduced density matrix depend on time in quantum quench dynamics. Further, we study the relaxation dynamics of a single electron coupled to Holstein phonons in all parameter regimes. In the adiabatic case a net energy transfer from electron to phonons happens and we provide an analytic formula for the relaxation time in the weak-coupling adiabatic regime. Another main topic in this thesis is thermalization in closed quantum many-body systems. Our first example is the temporal decay of Neel order in the one-dimensional Fermi-Hubbard model. We find evidence that the relaxation dynamics of spin-related quantities are, in the long-time regime, controlled by spin excitations. Further, we study the thermalization of the double occupancy in the framework of the eigenstate thermalization hypothesis and find that it does not thermalize due to integrability of the model. As a second example, we consider many-body localization in a one-dimensional system of spinless fermions with attractive interactions. It is known for

Numerical methods for strongly correlated many-body systems with bosonic degrees of freedom

Energy Technology Data Exchange (ETDEWEB)

Dorfner, Florian Guenter

2017-02-23

dimension also during time evolution. For the polaron problem on an infinite chain Krylov-space time evolution in a limited functional space has been shown to be very efficient. We adapt this algorithm to periodic boundary conditions and show that it is the most efficient method compared to standard Krylov space time evolution and the time-evolving block decimation method. We also study the properties of the local reduced density matrix as a function of model parameters and under non-equilibrium conditions in three different models: the Bose-Bose resonance model, the Holstein model and the Hubbard-Holstein model. It was shown for fermionic and spin models that the single-site von Neumann entropy is an indicator for phase transitions. In the Bose-Bose resonance model we find that both, the local von Neumann entropy and the eigenstates of the local reduced density matrix show features in the vicinity of a phase boundary. Also, we find that the eigenstates of the local reduced density matrix depend on time in quantum quench dynamics. Further, we study the relaxation dynamics of a single electron coupled to Holstein phonons in all parameter regimes. In the adiabatic case a net energy transfer from electron to phonons happens and we provide an analytic formula for the relaxation time in the weak-coupling adiabatic regime. Another main topic in this thesis is thermalization in closed quantum many-body systems. Our first example is the temporal decay of Neel order in the one-dimensional Fermi-Hubbard model. We find evidence that the relaxation dynamics of spin-related quantities are, in the long-time regime, controlled by spin excitations. Further, we study the thermalization of the double occupancy in the framework of the eigenstate thermalization hypothesis and find that it does not thermalize due to integrability of the model. As a second example, we consider many-body localization in a one-dimensional system of spinless fermions with attractive interactions. It is known for

Bose-Einstein correlations in W+ W- events at LEP2

CERN Document Server

van Dalen, Jorn A

2000-01-01

Analyses of Bose-Einstein Correlations in w+w- events at LEP2 by the four LEP collaborations are presented. In particular, Bose-Einstein correlations in w+w- overlap are investigated and the possible existence of these correlations between particles coming from different W's, which may influence the W mass measurements in the fully-hadronic channel e+e- --+ w+w- --+ qiihq3ij<. No evidence for such an inter-W Bose-Einstein correlation is found by L3 and ALEPH. Possible indication of these correlations by DELPHI is mentioned.

Superfluidity, Bose condensation and neutron scattering in liquid 4He

International Nuclear Information System (INIS)

Silver, R.N.

1997-01-01

The relation between superfluidity and Bose condensation in 4 He provides lessons that may be valuable in understanding the strongly correlated electron system of high T c superconductivity. Direct observation of a Bose condensate in the superfluid by deep inelastic neutron scattering measurements has been attempted over many years. But the impulse approximation, which relates momentum distributions to neutron scattering structure functions, is broadened by final state effects. Nevertheless, the excellent quantitative agreement between ab initio quantum many body theory and high precision neutron experiments provides confidence in the connection between superfluidity and Bose condensation

Bose-Einstein Correlations of $\\pi^{0}$ Pairs from Hadronic $Z^{0}$ Decays

CERN Document Server

Abbiendi, G.; Akesson, P.F.; Alexander, G.; Allison, John; Amaral, P.; Anagnostou, G.; Anderson, K.J.; Arcelli, S.; Asai, S.; Axen, D.; Azuelos, G.; Bailey, I.; Barberio, E.; Barlow, R.J.; Batley, R.J.; Bechtle, P.; Behnke, T.; Bell, Kenneth Watson; Bell, P.J.; Bella, G.; Bellerive, A.; Benelli, G.; Bethke, S.; Biebel, O.; Bloodworth, I.J.; Boeriu, O.; Bock, P.; Bonacorsi, D.; Boutemeur, M.; Braibant, S.; Brigliadori, L.; Brown, Robert M.; Buesser, K.; Burckhart, H.J.; Campana, S.; Carnegie, R.K.; Caron, B.; Carter, A.A.; Carter, J.R.; Chang, C.Y.; Charlton, David G.; Csilling, A.; Cuffiani, M.; Dado, S.; Dallison, S.; De Roeck, A.; De Wolf, E.A.; Desch, K.; Dienes, B.; Donkers, M.; Dubbert, J.; Duchovni, E.; Duckeck, G.; Duerdoth, I.P.; Elfgren, E.; Etzion, E.; Fabbri, F.; Feld, L.; Ferrari, P.; Fiedler, F.; Fleck, I.; Ford, M.; Frey, A.; Furtjes, A.; Gagnon, P.; Gary, John William; Gaycken, G.; Geich-Gimbel, C.; Giacomelli, G.; Giacomelli, P.; Giunta, Marina; Goldberg, J.; Gross, E.; Grunhaus, J.; Gruwe, M.; Gunther, P.O.; Gupta, A.; Hajdu, C.; Hamann, M.; Hanson, G.G.; Harder, K.; Harel, A.; Harin-Dirac, M.; Hauschild, M.; Hauschildt, J.; Hawkes, C.M.; Hawkings, R.; Hemingway, R.J.; Hensel, C.; Herten, G.; Heuer, R.D.; Hill, J.C.; Hoffman, Kara Dion; Homer, R.J.; Horvath, D.; Howard, R.; Igo-Kemenes, P.; Ishii, K.; Jeremie, H.; Jovanovic, P.; Junk, T.R.; Kanaya, N.; Kanzaki, J.; Karapetian, G.; Karlen, D.; Kartvelishvili, V.; Kawagoe, K.; Kawamoto, T.; Keeler, R.K.; Kellogg, R.G.; Kennedy, B.W.; Kim, D.H.; Klein, K.; Klier, A.; Kluth, S.; Kobayashi, T.; Kobel, M.; Komamiya, S.; Kormos, Laura L.; Kramer, T.; Kress, T.; Krieger, P.; von Krogh, J.; Krop, D.; Kruger, K.; Kuhl, T.; Kupper, M.; Lafferty, G.D.; Landsman, H.; Lanske, D.; Layter, J.G.; Leins, A.; Lellouch, D.; Lettso, J.; Levinson, L.; Lillich, J.; Lloyd, S.L.; Loebinger, F.K.; Lu, J.; Ludwig, J.; Macpherson, A.; Mader, W.; Marcellini, S.; Marchant, T.E.; Martin, A.J.; Martin, J.P.; Masetti, G.; Mashimo, T.; Mattig, Peter; McDonald, W.J.; McKenna, J.; McMahon, T.J.; McPherson, R.A.; Meijers, F.; Mendez-Lorenzo, P.; Menges, W.; Merritt, F.S.; Mes, H.; Michelini, A.; Mihara, S.; Mikenberg, G.; Miller, D.J.; Moed, S.; Mohr, W.; Mori, T.; Mutter, A.; Nagai, K.; Nakamura, I.; Neal, H.A.; Nisius, R.; O'Neale, S.W.; Oh, A.; Okpara, A.; Oreglia, M.J.; Orito, S.; Pahl, C.; Pasztor, G.; Pater, J.R.; Patrick, G.N.; Pilcher, J.E.; Pinfold, J.; Plane, David E.; Poli, B.; Polok, J.; Pooth, O.; Przybycien, M.; Quadt, A.; Rabbertz, K.; Rembser, C.; Renkel, P.; Rick, H.; Roney, J.M.; Rosati, S.; Rozen, Y.; Runge, K.; Sachs, K.; Saeki, T.; Sahr, O.; Sarkisyan, E.K.G.; Schaile, A.D.; Schaile, O.; Scharff-Hansen, P.; Schieck, J.; Schoerner-Sadenius, Thomas; Schroder, Matthias; Schumacher, M.; Schwick, C.; Scott, W.G.; Seuster, R.; Shears, T.G.; Shen, B.C.; Sherwood, P.; Siroli, G.; Skuja, A.; Smith, A.M.; Sobie, R.; Soldner-Rembold, S.; Spano, F.; Stahl, A.; Stephens, K.; Strom, David M.; Strohmer, R.; Tarem, S.; Tasevsky, M.; Taylor, R.J.; Teuscher, R.; Thomson, M.A.; Torrence, E.; Toya, D.; Tran, P.; Trefzger, T.; Tricoli, A.; Trigger, I.; Trocsanyi, Z.; Tsur, E.; Turner-Watson, M.F.; Ueda, I.; Ujvari, B.; Vachon, B.; Vollmer, C.F.; Vannerem, P.; Verzocchi, M.; Voss, H.; Vossebeld, J.; Waller, D.; Ward, C.P.; Ward, D.R.; Watkins, P.M.; Watson, A.T.; Watson, N.K.; Wells, P.S.; Wengler, T.; Wermes, N.; Wetterling, D.; Wilson, G.W.; Wilson, J.A.; Wolf, G.; Wyatt, T.R.; Yamashita, S.; Zer-Zion, D.; Zivkovic, Lidija

2003-01-01

We observed Bose-Einstein correlation in pi0 pairs produced in Z0 decays using the data sample collected by the OPAL detector at LEP 1 from 1991 to 1995. Using a static Gaussian picture for the pion emitter source, we obtain the chaoticity parameter lambda = 0.55 +- 0.10 +- 0.10 and the source radius R = (0.59 +- 0.08 +- 0.05) fm. according to the JETSET and HERWIG Monte Carlo models, the Bose-Einstein correlations in our data sample largely connect pi0s originating from the decays of different hadrons. Prompt pions formed at string break-up of cluster decays only form a small fraction of the sample.

Engineering frequency-dependent superfluidity in Bose-Fermi mixtures

Science.gov (United States)

Arzamasovs, Maksims; Liu, Bo

2018-04-01

Unconventional superconductivity and superfluidity are among the most exciting and fascinating quantum phenomena in condensed-matter physics. Usually such states are characterized by nontrivial spin or spatial symmetry of the pairing order parameter, such as "spin triplet" or "p wave." However, besides spin and spatial dependence the order parameter may have unconventional frequency dependence which is also permitted by Fermi-Dirac statistics. Odd-frequency fermionic pairing is an exciting paradigm when discussing exotic superfluidity or superconductivity and is yet to be realized in experiments. In this paper we propose a symmetry-based method of controlling frequency dependence of the pairing order parameter via manipulating the inversion symmetry of the system. First, a toy model is introduced to illustrate that frequency dependence of the order parameter can be achieved through our proposed approach. Second, by taking advantage of recent rapid developments in producing spin-orbit-coupled dispersions in ultracold gases, we propose a Bose-Fermi mixture to realize such frequency-dependent superfluid. The key idea is introducing the frequency-dependent attraction between fermions mediated by Bogoliubov phonons with asymmetric dispersion. Our proposal should pave an alternative way for exploring frequency-dependent superfluids with cold atoms.

Implementation of the Lanczos algorithm for the Hubbard model on the Connection Machine system

International Nuclear Information System (INIS)

Leung, P.W.; Oppenheimer, P.E.

1992-01-01

An implementation of the Lanczos algorithm for the exact diagonalization of the two dimensional Hubbard model on a 4x4 square lattice on the Connection Machine CM-2 system is described. The CM-2 is a massively parallel machine with distributed memory. The program is written in C/PARIS. This implementation minimizes memory usage by generating the matrix elements as needed instead of storing them. The Lanczos vectors are stored across the local memory of the processors. Using translational symmetry only, the dimension of the Hilbert space at half filling is more than 10 million. A speed of about 2.4 min per iteration is achieved on a 64K CM-2. This implementation is scalable. Running it on a bigger machine with more processors speeds up the process. The performance analysis of this implementation is shown and discuss its advantages and disadvantages are discussed

Studies on entanglement entropy for Hubbard model with hole-doping and external magnetic field

International Nuclear Information System (INIS)

Yao, K.L.; Li, Y.C.; Sun, X.Z.; Liu, Q.M.; Qin, Y.; Fu, H.H.; Gao, G.Y.

2005-01-01

By using the density matrix renormalization group (DMRG) method for the one-dimensional (1D) Hubbard model, we have studied the von Neumann entropy of a quantum system, which describes the entanglement of the system block and the rest of the chain. It is found that there is a close relation between the entanglement entropy and properties of the system. The hole-doping can alter the charge-charge and spin-spin interactions, resulting in charge polarization along the chain. By comparing the results before and after the doping, we find that doping favors increase of the von Neumann entropy and thus also favors the exchange of information along the chain. Furthermore, we calculated the spin and entropy distribution in external magnetic filed. It is confirmed that both the charge-charge and the spin-spin interactions affect the exchange of information along the chain, making the entanglement entropy redistribute

Random-phase-approximation approach to optical and magnetic excitations in the two-dimensional multiband Hubbard model

International Nuclear Information System (INIS)

Yonemitsu, K.; Bishop, A.R.

1992-01-01

As a convenient qualitative approach to strongly correlated electronic systems, an inhomogeneous Hartree-Fock plus random-phase approximation is applied to response functions for the two-dimensional multiband Hubbard model for cuprate superconductors. A comparison of the results with those obtained by exact diagonalization by Wagner, Hanke, and Scalapino [Phys. Rev. B 43, 10 517 (1991)] shows that overall structures in optical and magnetic particle-hole excitation spectra are well reproduced by this method. This approach is computationally simple, retains conceptual clarity, and can be calibrated by comparison with exact results on small systems. Most importantly, it is easily extended to larger systems and straightforward to incorporate additional terms in the Hamiltonian, such as electron-phonon interactions, which may play a crucial role in high-temperature superconductivity

Energy transfer in coupled nonlinear phononic waveguides: transition from wandering breather to nonlinear self-trapping

International Nuclear Information System (INIS)

Kosevich, Y A; Manevitch, L I; Savin, A V

2007-01-01

We consider, both analytically and numerically, the dynamics of stationary and slowly-moving breathers (localized short-wavelength excitations) in two weakly coupled nonlinear oscillator chains (nonlinear phononic waveguides). We show that there are two qualitatively different dynamical regimes of the coupled breathers: the oscillatory exchange of the low-amplitude breather between the phononic waveguides (wandering breather), and one-waveguide-localization (nonlinear self-trapping) of the high-amplitude breather. We also show that phase-coherent dynamics of the coupled breathers in two weakly linked nonlinear phononic waveguides has a profound analogy, and is described by a similar pair of equations, to the tunnelling quantum dynamics of two weakly linked Bose-Einstein condensates in a symmetric double-well potential (single bosonic Josephson junction). The exchange of phonon energy and excitations between the coupled phononic waveguides takes on the role which the exchange of atoms via quantum tunnelling plays in the case of the coupled condensates. On the basis of this analogy, we predict a new tunnelling mode of the coupled Bose-Einstein condensates in a single bosonic Josephson junction in which their relative phase oscillates around π/2. The dynamics of relative phase of two weakly linked Bose-Einstein condensates can be studied by means of interference, while the dynamics of the exchange of lattice excitations in coupled nonlinear phononic waveguides can be observed by means of light scattering

Bose-Einstein condensation in helium white dwarf stars. I

Energy Technology Data Exchange (ETDEWEB)

Mosquera, M.E. [Faculty of Astronomy and Geophysics, University of La Plata, Paseo del Bosque s.n., La Plata (Argentina); Department of Physics, University of La Plata, c.c. 67 1900, La Plata (Argentina); Civitarese, O., E-mail: osvaldo.civitarese@fisica.unlp.edu.a [Department of Physics, University of La Plata, c.c. 67 1900, La Plata (Argentina); Benvenuto, O.G.; De Vito, M.A. [Faculty of Astronomy and Geophysics, University of La Plata, Paseo del Bosque s.n., La Plata (Argentina); Instituto de Astrofisica La Plata, CCT (Argentina)

2010-01-18

The formation of a Bose-Einstein condensate in the interior of helium white dwarfs stars is discussed. Following the proposal made by Gabadadze and Rosen, we have explored the consequences of such a mechanism by calculating the cooling time of the stars. We have found that it is shorter than the value predicted by the standard model.

Bose-Einstein condensation and crystallization

International Nuclear Information System (INIS)

Suetoe, A.

2008-01-01

The paper describes history and state of art theory of Bose-Einstein condensation and crystallization as cases of breaking continuous symmetries. Emphasizes that these problems have not been solved exactly. (TRA)

Solution of the statistical bootstrap with Bose statistics

International Nuclear Information System (INIS)

Engels, J.; Fabricius, K.; Schilling, K.

1977-01-01

A brief and transparent way to introduce Bose statistics into the statistical bootstrap of Hagedorn and Frautschi is presented. The resulting bootstrap equation is solved by a cluster expansion for the grand canonical partition function. The shift of the ultimate temperature due to Bose statistics is determined through an iteration process. We discuss two-particle spectra of the decaying fireball (with given mass) as obtained from its grand microcanonical level density

Merging and splitting of Bose-Einstein condensates into two translating traps

International Nuclear Information System (INIS)

Sun, B; Pindzola, M S

2009-01-01

We investigate the process of merging and splitting Bose-Einstein condensates into two slowly translating traps, analogous to a dual input atomic beam splitter. With the help of direct three-dimensional numerical simulations, we explore the dependence of population distributions on the initial relative phase and the trap moving speed. For non-interacting Bose-Einstein condensates, we find that our numerical results are in good agreement with a simple theoretical prediction. However, for interacting Bose-Einstein condensates, our results show striking differences with the non-interacting case: the Bose-Einstein condensates are always split towards 50:50 in the slow translation regime. This bosonic anti-bunching effect is interpreted as a consequence of complicated flow patterns due to atomic interactions.

Cavity assisted measurements of heat and work in optical lattices

Directory of Open Access Journals (Sweden)

Louis Villa

2018-01-01

Full Text Available We propose a method to experimentally measure the internal energy of a system of ultracold atoms trapped in optical lattices by coupling them to the fields of two optical cavities. We show that the tunnelling and self-interaction terms of the one-dimensional Bose-Hubbard Hamiltonian can be mapped to the field and photon number of each cavity, respectively. We compare the energy estimated using this method with numerical results obtained using the density matrix renormalisation group algorithm. Our method can be employed for the assessment of power and efficiency of thermal machines whose working substance is a strongly correlated many-body system.

Perturbation expansion of the ground-state energy for the one-dimensional cyclic Hubbard system in the Hueckel limit

International Nuclear Information System (INIS)

Takahashi, M.; Bracken, P.; Cizek, J.; Paldus, J.

1995-01-01

The perturbation expansion coefficients for the ground-state energy of the half-filled one-dimensional Hubbard model with N = 4 ν + 2, (ν = 1,2,...) sites and satisfying cyclic boundary conditions were calculated in the Hueckel limit (U/β → 0), where β designates the one-electron hopping or resonance integral, and U, the two-electron on-site Coulomb integral. This was achieved by solving-order by order-the Lieb-Wu equations, a system of transcendental equations that determines the set of quasi-momenta (k i ) and spin variable τ α for this model. The exact values for these quantities were found for the N = 6 member ring up to the 20th order in terms of the coupling constant B = U/2β, as well as numerically for 10 ≤ N ≤ 50, and the N = 6 Lieb-Wu system was reduced to a system of sextic algebraic equations. These results are compared with those of the infinite system derived analytically by Misurkin and Ovchinnikov. It is further shown how the results of this article can be used for the interpolation by the root of a polynomial. It is demonstrated that a polynomial of relatively small degree provides a very good approximation for the energy in the intermediate coupling region. 20 refs., 3 tabs

Bose and his statistics

International Nuclear Information System (INIS)

Venkataraman, G.

1992-01-01

Treating radiation gas as a classical gas, Einstein derived Planck's law of radiation by considering the dynamic equilibrium between atoms and radiation. Dissatisfied with this treatment, S.N. Bose derived Plank's law by another original way. He treated the problem in generality: he counted how many cells were available for the photon gas in phase space and distributed the photons into these cells. In this manner of distribution, there were three radically new ideas: The indistinguishability of particles, the spin of the photon (with only two possible orientations) and the nonconservation of photon number. This gave rise to a new discipline of quantum statistical mechanics. Physics underlying Bose's discovery, its significance and its role in development of the concept of ideal gas, spin-statistics theorem and spin particles are described. The book has been written in a simple and direct language in an informal style aiming to stimulate the curiosity of a reader. (M.G.B.)

Origami rules for the construction of localized eigenstates of the Hubbard model in decorated lattices

Science.gov (United States)

Dias, R. G.; Gouveia, J. D.

2015-11-01

We present a method of construction of exact localized many-body eigenstates of the Hubbard model in decorated lattices, both for U = 0 and U → ∞. These states are localized in what concerns both hole and particle movement. The starting point of the method is the construction of a plaquette or a set of plaquettes with a higher symmetry than that of the whole lattice. Using a simple set of rules, the tight-binding localized state in such a plaquette can be divided, folded and unfolded to new plaquette geometries. This set of rules is also valid for the construction of a localized state for one hole in the U → ∞ limit of the same plaquette, assuming a spin configuration which is a uniform linear combination of all possible permutations of the set of spins in the plaquette.

Bose Condensate in He II

International Nuclear Information System (INIS)

Svensson, E.C.

1984-01-01

The Condensate Saga, now halfway through its fifth decade, is reviewed. The recent neutron-scattering work which has at last convincingly established that there is indeed a Bose Condensate in He II is described

Bose-Einstein condensation in microgravity.

Science.gov (United States)

van Zoest, T; Gaaloul, N; Singh, Y; Ahlers, H; Herr, W; Seidel, S T; Ertmer, W; Rasel, E; Eckart, M; Kajari, E; Arnold, S; Nandi, G; Schleich, W P; Walser, R; Vogel, A; Sengstock, K; Bongs, K; Lewoczko-Adamczyk, W; Schiemangk, M; Schuldt, T; Peters, A; Könemann, T; Müntinga, H; Lämmerzahl, C; Dittus, H; Steinmetz, T; Hänsch, T W; Reichel, J

2010-06-18

Albert Einstein's insight that it is impossible to distinguish a local experiment in a "freely falling elevator" from one in free space led to the development of the theory of general relativity. The wave nature of matter manifests itself in a striking way in Bose-Einstein condensates, where millions of atoms lose their identity and can be described by a single macroscopic wave function. We combine these two topics and report the preparation and observation of a Bose-Einstein condensate during free fall in a 146-meter-tall evacuated drop tower. During the expansion over 1 second, the atoms form a giant coherent matter wave that is delocalized on a millimeter scale, which represents a promising source for matter-wave interferometry to test the universality of free fall with quantum matter.

Topological Coherent Modes in Trapped Bose Gas

International Nuclear Information System (INIS)

Yukalov, V.I.; Marzlin, K.-P.; Yukalova, E.P.; Bagnato, V.S.

2005-01-01

The report reviews the problem of topological coherent modes, which are nonlinear collective states of Bose-condensed atoms. Such modes can be generated by means of alternating external fields, whose frequencies are in resonance with the transition frequencies between the related modes. The Bose gas with generated topological coherent modes is a collective nonlinear analog of a resonant atom. Such systems exhibit a variety of nontrivial effects, e.g. interference fringes, interference current, mode locking, dynamic transitions, critical phenomena, chaotic motion, harmonic generation, parametric conversion, atomic squeezing, and entanglement production

Scenario of strongly nonequilibrated Bose-Einstein condensation

International Nuclear Information System (INIS)

Berloff, Natalia G.; Svistunov, Boris V.

2002-01-01

Large scale numerical simulations of the Gross-Pitaevskii equation are used to elucidate the self-evolution of a Bose gas from a strongly nonequilibrium initial state. The stages of the process confirm and refine the theoretical scenario of Bose-Einstein condensation developed by Svistunov and co-workers [J. Mosc. Phys. Soc. 1, 373 (1991); Sov. Phys. JETP 75, 387 (1992); 78, 187 (1994)]: the system evolves from the regime of weak turbulence to superfluid turbulence via states of strong turbulence in the long-wavelength region of energy space

Angular Momentum of a Bose-Einstein Condensate in a Synthetic Rotational Field

Science.gov (United States)

Qu, Chunlei; Stringari, Sandro

2018-05-01

By applying a position-dependent detuning to a spin-orbit-coupled Hamiltonian with equal Rashba and Dresselhaus coupling, we exploit the behavior of the angular momentum of a harmonically trapped Bose-Einstein condensed atomic gas and discuss the distinctive role of its canonical and spin components. By developing the formalism of spinor hydrodynamics, we predict the precession of the dipole oscillation caused by the synthetic rotational field, in analogy with the precession of the Foucault pendulum, the excitation of the scissors mode, following the sudden switching off of the detuning, and the occurrence of Hall-like effects. When the detuning exceeds a critical value, we observe a transition from a vortex free, rigidly rotating quantum gas to a gas containing vortices with negative circulation which results in a significant reduction of the total angular momentum.

Ultra-cold molecules in an atomic Bose-Einstein condensate

Science.gov (United States)

Wynar, Roahn Helden

2000-08-01

This thesis is about photoassociation of Bose-condensed 87Rb. Most importantly we report that state selected 87Rb2 molecules were created at rest in a condensate of 87Rb using two-photon photoassociation. Additionally, we have identified three weakly bound states of the 87Rb2 S+u3 , potential for the |1, -1> + |1, - 1> collisional channel. The binding energies of these states are 529.4 +/- .07, 636.0094 +/- .0012, and 24.24 +/- .01 MHz respectively. We have also carried out a detailed study of the density dependence of the shift and width of the two-photon lineshape. This shift and width is modeled using the theory of Bohn and Julienne [34] and in addition to the precise measurement of binding energy we also report the first measurement of an atom molecule scattering length, aam, which we conclude is -180 +/- 150 a0, and the inelastic collision rate, Kinel dependent coherent coupling between atoms and molecules. This theory yields two coupled equations, one for the evolution of atomic condensate amplitude and one for the evolution of molecular condensate amplitude. The nature of the atomic-molecular condensate evolution is shown to depend on six, model parameters including the coherent coupling, given by cn . The other five parameters can be interpreted as light-shifts and incoherent loss rates. We present a calculation intended to estimate the values of these six parameters for the 87Rb - 87Rb 2 system. Based on the results of this calculation we identify two locations in the 87Rb2 spectrum where coherent transfer of population from atomic condensate to molecular condensate is plausible. Finally, we examine the credibility of the theoretical model used to estimate the six parameters used by the mean field theory. By comparing the measured Stark shifts of two-color resonances with predictions based on our theoretical model we conclude that the model is satisfactory for the v = 37 level of the S+u3 potential. This work also describes the experimental details of

Correlation Functions of the One-Dimensional Attractive Bose Gas

International Nuclear Information System (INIS)

Calabrese, Pasquale; Caux, Jean-Sebastien

2007-01-01

The zero-temperature correlation functions of the one-dimensional attractive Bose gas with a delta-function interaction are calculated analytically for any value of the interaction parameter and number of particles, directly from the integrability of the model. We point out a number of interesting features, including zero recoil energy for a large number of particles, analogous to the Moessbauer effect

Functional-derivative study of the Hubbard model. III. Fully renormalized Green's function

International Nuclear Information System (INIS)

Arai, T.; Cohen, M.H.

1980-01-01

The functional-derivative method of calculating the Green's function developed earlier for the Hubbard model is generalized and used to obtain a fully renormalized solution. Higher-order functional derivatives operating on the basic Green's functions, G and GAMMA, are all evaluated explicitly, thus making the solution applicable to the narrow-band region as well as the wide-band region. Correction terms Phi generated from functional derivatives of equal-time Green's functions of the type delta/sup n/ /deltaepsilon/sup n/, etc., with n > or = 2. It is found that the Phi's are, in fact, renormalization factors involved in the self-energy Σ and that the structure of the Phi's resembles that of Σ and contains the same renormalization factors Phi. The renormalization factors Phi are shown to satisfy a set of equations and can be evaluated self-consistently. In the presence of the Phi's, all difficulties found in the previous results (papers I and II) are removed, and the energy spectrum ω can now be evaluated for all occupations n. The Schwinger relation is the only basic relation used in generating this fully self-consistent Green's function, and the Baym-Kadanoff continuity condition is automatically satisfied

Generalized N-coupled maps with invariant measure in Bose ...

Indian Academy of Sciences (India)

chronization problem of an array of the linearly coupled map lattices of ... groups and graphs and also in the design of experiments, coding theory, partition ... coupled map lattice which covers internal and external couplings in a form of asso-.

Dicke superradiance as nondestructive probe for the state of atoms in optical lattices

Science.gov (United States)

ten Brinke, Nicolai; Schützhold, Ralf

2016-04-01

We present a proposal for a probing scheme utilizing Dicke superradiance to obtain information about ultracold atoms in optical lattices. A probe photon is absorbed collectively by an ensemble of lattice atoms generating a Dicke state. The lattice dynamics (e.g., tunneling) affects the coherence properties of that Dicke state and thus alters the superradiant emission characteristics - which in turn provides insight into the lattice (dynamics). Comparing the Bose-Hubbard and the Fermi-Hubbard model, we find similar superradiance in the strongly interacting Mott insulator regime, but crucial differences in the weakly interacting (superfluid or metallic) phase. Furthermore, we study the possibility to detect whether a quantum phase transition between the two regimes can be considered adiabatic or a quantum quench.

The shear viscosity of a trapped Bose-condensed gas

International Nuclear Information System (INIS)

Shahzamanian, M.A.; Yavary, H.

2006-01-01

By obtaining Kubo formula type and using nonequilibrium Green's functions, we calculate the shear viscosity of a trapped Bose-condensed gas below and above the Bose-Einstein condensation temperature (T BEC ). The contributions of the interactions between condensate and noncondensate atoms and between noncondensate atoms take into account to the viscous relaxation time, by evaluating second order self-energies in Beliaev approximation

Equilibrium and off-equilibrium trap-size scaling in one-dimensional ultracold bosonic gases

International Nuclear Information System (INIS)

Campostrini, Massimo; Vicari, Ettore

2010-01-01

We study some aspects of equilibrium and off-equilibrium quantum dynamics of dilute bosonic gases in the presence of a trapping potential. We consider systems with a fixed number of particles and study their scaling behavior with increasing the trap size. We focus on one-dimensional bosonic systems, such as gases described by the Lieb-Liniger model and its Tonks-Girardeau limit of impenetrable bosons, and gases constrained in optical lattices as described by the Bose-Hubbard model. We study their quantum (zero-temperature) behavior at equilibrium and off equilibrium during the unitary time evolution arising from changes of the trapping potential, which may be instantaneous or described by a power-law time dependence, starting from the equilibrium ground state for an initial trap size. Renormalization-group scaling arguments and analytical and numerical calculations show that the trap-size dependence of the equilibrium and off-equilibrium dynamics can be cast in the form of a trap-size scaling in the low-density regime, characterized by universal power laws of the trap size, in dilute gases with repulsive contact interactions and lattice systems described by the Bose-Hubbard model. The scaling functions corresponding to several physically interesting observables are computed. Our results are of experimental relevance for systems of cold atomic gases trapped by tunable confining potentials.

Fermionic models with superconducting circuits

Energy Technology Data Exchange (ETDEWEB)

Las Heras, Urtzi; Garcia-Alvarez, Laura; Mezzacapo, Antonio; Lamata, Lucas [University of the Basque Country UPV/EHU, Department of Physical Chemistry, Bilbao (Spain); Solano, Enrique [University of the Basque Country UPV/EHU, Department of Physical Chemistry, Bilbao (Spain); IKERBASQUE, Basque Foundation for Science, Bilbao (Spain)

2015-12-01

We propose a method for the efficient quantum simulation of fermionic systems with superconducting circuits. It consists in the suitable use of Jordan-Wigner mapping, Trotter decomposition, and multiqubit gates, be with the use of a quantum bus or direct capacitive couplings. We apply our method to the paradigmatic cases of 1D and 2D Fermi-Hubbard models, involving couplings with nearest and next-nearest neighbours. Furthermore, we propose an optimal architecture for this model and discuss the benchmarking of the simulations in realistic circuit quantum electrodynamics setups. (orig.)

Bipolarons in one-dimensional extended Peierls-Hubbard models

Science.gov (United States)

Sous, John; Chakraborty, Monodeep; Krems, Roman; Berciu, Mona

2017-04-01

We study two particles in an infinite chain and coupled to phonons by interactions that modulate their hopping as described by the Peierls/Su-Schrieffer-Heeger (SSH) model. In the case of hard-core bare particles, we show that exchange of phonons generates effective nearest-neighbor repulsion between particles and also gives rise to interactions that move the pair as a whole. The two-polaron phase diagram exhibits two sharp transitions, leading to light dimers at strong coupling and the flattening of the dimer dispersion at some critical values of the parameters. This dimer (quasi)self-trapping occurs at coupling strengths where single polarons are mobile. On the other hand, in the case of soft-core particles/ spinfull fermions, we show that phonon-mediated interactions are attractive and result in strongly bound and mobile bipolarons in a wide region of parameter space. This illustrates that, depending on the strength of the phonon-mediated interactions and statistics of bare particles, the coupling to phonons may completely suppress or strongly enhance quantum transport of correlated particles. This work was supported by NSERC of Canada and the Stewart Blusson Quantum Matter Institute.

Non-equilibrium coherence dynamics in one-dimensional Bose gases

DEFF Research Database (Denmark)

Hofferberth, S.; Lesanovsky, Igor; Fischer, B.

2007-01-01

Low-dimensional systems provide beautiful examples of many-body quantum physics. For one-dimensional (1D) systems, the Luttinger liquid approach provides insight into universal properties. Much is known of the equilibrium state, both in the weakly and strongly interacting regimes. However......, the coherence factor is observed to approach a non-zero equilibrium value, as predicted by a Bogoliubov approach. This coupled-system decay to finite coherence is the matter wave equivalent of phase-locking two lasers by injection. The non-equilibrium dynamics of superfluids has an important role in a wide...... range of physical systems, such as superconductors, quantum Hall systems, superfluid helium and spin systems. Our experiments studying coherence dynamics show that 1D Bose gases are ideally suited for investigating this class of phenomena....

Approaching Bose-Einstein Condensation

Science.gov (United States)

Ferrari, Loris

2011-01-01

Bose-Einstein condensation (BEC) is discussed at the level of an advanced course of statistical thermodynamics, clarifying some formal and physical aspects that are usually not covered by the standard pedagogical literature. The non-conventional approach adopted starts by showing that the continuum limit, in certain cases, cancels out the crucial…

Faraday waves in Bose-Einstein condensates

International Nuclear Information System (INIS)

Nicolin, Alexandru I.; Carretero-Gonzalez, R.; Kevrekidis, P. G.

2007-01-01

Motivated by recent experiments on Faraday waves in Bose-Einstein condensates we investigate both analytically and numerically the dynamics of cigar-shaped Bose-condensed gases subject to periodic modulation of the strength of the transverse confinement. We offer a fully analytical explanation of the observed parametric resonance, based on a Mathieu-type analysis of the non-polynomial Schroedinger equation. The theoretical prediction for the pattern periodicity versus the driving frequency is directly compared to the experimental data, yielding good qualitative and quantitative agreement between the two. These results are corroborated by direct numerical simulations of both the one-dimensional non-polynomial Schroedinger equation and of the fully three-dimensional Gross-Pitaevskii equation

Relevance of Bose-Einstein condensation to the interference of two independent Bose gases

International Nuclear Information System (INIS)

Iazzi, Mauro; Yuasa, Kazuya

2011-01-01

Interference of two independently prepared ideal Bose gases is discussed, on the basis of the idea of measurement-induced interference. It is known that, even if the number of atoms in each gas is individually fixed finite and the symmetry of the system is not broken, an interference pattern is observed on each single snapshot. The key role is played by the Hanbury Brown and Twiss effect, which leads to an oscillating pattern of the cloud of identical atoms. Then, how essential is the Bose-Einstein condensation to the interference? In this work, we describe two ideal Bose gases trapped in two separate three-dimensional harmonic traps at a finite temperature T, using the canonical ensembles (with fixed numbers of atoms). We compute the full statistics of the snapshot profiles of the expanding and overlapping gases released from the traps. We obtain a simple formula valid for finite T, which shows that the average fringe spectrum (average fringe contrast) is given by the purity of each gas. The purity is known to be a good measure of condensation, and the formula clarifies the relevance of the condensation to the interference. The results for T=0, previously known in the literature, can be recovered from our analysis. The fluctuation of the interference spectrum is also studied, and it is shown that the fluctuation is vanishingly small only below the critical temperature T c , meaning that interference pattern is certainly observed on every snapshot below T c . The fact that the number of atoms is fixed in the canonical ensemble is crucial to this vanishing fluctuation.

Condensate fluctuations of interacting Bose gases within a microcanonical ensemble.

Science.gov (United States)

Wang, Jianhui; He, Jizhou; Ma, Yongli

2011-05-01

Based on counting statistics and Bogoliubov theory, we present a recurrence relation for the microcanonical partition function for a weakly interacting Bose gas with a finite number of particles in a cubic box. According to this microcanonical partition function, we calculate numerically the distribution function, condensate fraction, and condensate fluctuations for a finite and isolated Bose-Einstein condensate. For ideal and weakly interacting Bose gases, we compare the condensate fluctuations with those in the canonical ensemble. The present approach yields an accurate account of the condensate fluctuations for temperatures close to the critical region. We emphasize that the interactions between excited atoms turn out to be important for moderate temperatures.

Damping at positive frequencies in the limit J⊥-->0 in the strongly correlated Hubbard model

Science.gov (United States)

Mohan, Minette M.

1992-08-01

I show damping in the two-dimensional strongly correlated Hubbard model within the retraceable-path approximation, using an expansion around dominant poles for the self-energy. The damping half-width ~J2/3z occurs only at positive frequencies ω>5/2Jz, the excitation energy of a pure ``string'' state of length one, where Jz is the Ising part of the superexchange interaction, and occurs even in the absence of spin-flip terms ~J⊥ in contrast to other theoretical treatments. The dispersion relation for both damped and undamped peaks near the upper band edge is found and is shown to have lost the simple J2/3z dependence characteristic of the peaks near the lower band edge. The position of the first three peaks near the upper band edge agrees well with numerical simulations on the t-J model. The weight of the undamped peaks near the upper band edge is ~J4/3z, contrasting with Jz for the weight near the lower band edge.

Realization of a scenario with two relaxation rates in the Hubbard Falicov-Kimball model

Science.gov (United States)

Barman, H.; Laad, M. S.; Hassan, S. R.

2018-02-01

A single transport relaxation rate governs the decay of both longitudinal and Hall currents in Landau Fermi liquids (FL). Breakdown of this fundamental feature, first observed in two-dimensional cuprates and subsequently in other three-dimensional correlated systems close to the Mott metal-insulator transition, played a pivotal role in emergence of a non-FL (NFL) paradigm in higher dimensions D (>1 ) . Motivated hereby, we explore the emergence of this "two relaxation rates" scenario in the Hubbard Falicov-Kimball model (HFKM) using the dynamical mean-field theory (DMFT). Specializing to D =3 , we find, beyond a critical Falicov-Kimball (FK) interaction, that two distinct relaxation rates governing distinct temperature (T ) dependence of the longitudinal and Hall currents naturally emerges in the NFL metal. Our results show good accord with the experiment in V2 -yO3 near the metal-to-insulator transition (MIT). We rationalize this surprising finding by an analytical analysis of the structure of charge and spin Hamiltonians in the underlying impurity problem, specifically through a bosonization method applied to the Wolff model and connecting it to the x-ray edge problem.

Existence of Bose-Einstein condensation in one and two dimensions

International Nuclear Information System (INIS)

Olinto, A.C.

1988-10-01

It is shown that in Bose Condensed systems the γ-sum rule has an additional term due to the condensate reservoir. As a result of this new sum rule and an exact Bogoliubov inequality, Bose-Einstein condensation in repulsively interacting systems may occur in one and two dimensions. (author) [pt

Yang—Yang thermodynamics of one-dimensional Bose gases with anisotropic transversal confinement

International Nuclear Information System (INIS)

Hao Ya-Jiang; Yin Xiang-Guo

2011-01-01

By combining the thermodynamic Bethe ansatz and local density approximation, we investigate the Yang—Yang thermodynamics of interacting one-dimensional Bose gases with anisotropic transversal confinement. It is shown that with the increase of anisotropic parameter at low temperature, the Bose atoms are distributed over a wider region, while at high temperature the density distribution is not affected obviously. Both the temperature and transversal confinement can strengthen the local pressure of the Bose gases. (general)

Extended ΛCDM: generalized non-minimal coupling for dark matter fluids

International Nuclear Information System (INIS)

Bettoni, Dario; Liberati, Stefano; Sindoni, Lorenzo

2011-01-01

In this paper we discuss a class of models that address the issue of explaining the gravitational dynamics at the galactic scale starting from a geometric point of view. Instead of claiming the existence of some hidden coupling between dark matter and baryons, or abandoning the existence of dark matter itself, we consider the possibility that dark matter and gravity have some non trivial interaction able to modify the dynamics at astrophysical scales. This interaction is implemented assuming that dark matter gets non-minimally coupled with gravity at suitably small scales and late times. After showing the predictions of the model in the Newtonian limit we also discuss the possible origin of it non-minimal coupling. This investigation seems to suggest that phenomenological mechanisms envisaged for the dark matter dynamics, such as the Bose-Einstein condensation of dark matter halos, could be connected to this class of models

Bose-Einstein condensation of light: general theory.

Science.gov (United States)

Sob'yanin, Denis Nikolaevich

2013-08-01

A theory of Bose-Einstein condensation of light in a dye-filled optical microcavity is presented. The theory is based on the hierarchical maximum entropy principle and allows one to investigate the fluctuating behavior of the photon gas in the microcavity for all numbers of photons, dye molecules, and excitations at all temperatures, including the whole critical region. The master equation describing the interaction between photons and dye molecules in the microcavity is derived and the equivalence between the hierarchical maximum entropy principle and the master equation approach is shown. The cases of a fixed mean total photon number and a fixed total excitation number are considered, and a much sharper, nonparabolic onset of a macroscopic Bose-Einstein condensation of light in the latter case is demonstrated. The theory does not use the grand canonical approximation, takes into account the photon polarization degeneracy, and exactly describes the microscopic, mesoscopic, and macroscopic Bose-Einstein condensation of light. Under certain conditions, it predicts sub-Poissonian statistics of the photon condensate and the polarized photon condensate, and a universal relation takes place between the degrees of second-order coherence for these condensates. In the macroscopic case, there appear a sharp jump in the degrees of second-order coherence, a sharp jump and kink in the reduced standard deviations of the fluctuating numbers of photons in the polarized and whole condensates, and a sharp peak, a cusp, of the Mandel parameter for the whole condensate in the critical region. The possibility of nonclassical light generation in the microcavity with the photon Bose-Einstein condensate is predicted.

Bose condensation in an attractive fermion gas: From weak to strong coupling superconductivity

International Nuclear Information System (INIS)

Nozieres, P.; Schmitt-Rink, S.

1985-01-01

We consider a gas of fermions interacting via an attractive potential. We study the ground state of that system and calculate the critical temperature for the onset of superconductivity as a function of the coupling strength. We compare the behavior of continuum and lattice models and show that the evolution from weak to strong coupling superconductivity is smooth

Higher order Bose-Einstein correlations in identical particle production

International Nuclear Information System (INIS)

Biyajima, M.

1990-01-01

A diagram technique to calculate the higher order Bose-Einstein correlations is formulated. This technique is applied to derive explicit expressions for the n-pion correlation functions for n = 2, 3, 4, and 5, and numerical predictions are given. In a comparison with the AFS and NA23 data on two-pion and three-pion Bose-Einstein correlations good agreement is obtained. 21 refs., 5 figs. (Authors)

Mesoscopic effects in quantum phases of ultracold quantum gases in optical lattices

International Nuclear Information System (INIS)

Carr, L. D.; Schirmer, D. G.; Wall, M. L.; Brown, R. C.; Williams, J. E.; Clark, Charles W.

2010-01-01

We present a wide array of quantum measures on numerical solutions of one-dimensional Bose- and Fermi-Hubbard Hamiltonians for finite-size systems with open boundary conditions. Finite-size effects are highly relevant to ultracold quantum gases in optical lattices, where an external trap creates smaller effective regions in the form of the celebrated 'wedding cake' structure and the local density approximation is often not applicable. Specifically, for the Bose-Hubbard Hamiltonian we calculate number, quantum depletion, local von Neumann entropy, generalized entanglement or Q measure, fidelity, and fidelity susceptibility; for the Fermi-Hubbard Hamiltonian we also calculate the pairing correlations, magnetization, charge-density correlations, and antiferromagnetic structure factor. Our numerical method is imaginary time propagation via time-evolving block decimation. As part of our study we provide a careful comparison of canonical versus grand canonical ensembles and Gutzwiller versus entangled simulations. The most striking effect of finite size occurs for bosons: we observe a strong blurring of the tips of the Mott lobes accompanied by higher depletion, and show how the location of the first Mott lobe tip approaches the thermodynamic value as a function of system size.

Non-Fermi Liquid Behavior and Continuously Tunable Resistivity Exponents in the Anderson-Hubbard Model at Finite Temperature

Energy Technology Data Exchange (ETDEWEB)

Patel, Niravkumar D. [The Univ. of Tennessee, Knoxville, TN (United States); Mukherjee, Anamitra [National Institute of Science Education and Research, Jatni (India); Kaushal, Nitin [The Univ. of Tennessee, Knoxville, TN (United States); Moreo, Adriana [The Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Dagotto, Elbio R. [The Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

2017-08-24

Here, we employ a recently developed computational many-body technique to study for the first time the half-filled Anderson-Hubbard model at finite temperature and arbitrary correlation U and disorder V strengths. Interestingly, the narrow zero temperature metallic range induced by disorder from the Mott insulator expands with increasing temperature in a manner resembling a quantum critical point. Our study of the resistivity temperature scaling T^α for this metal reveals non-Fermi liquid characteristics. Moreover, a continuous dependence of α on U and V from linear to nearly quadratic is observed. We argue that these exotic results arise from a systematic change with U and V of the “effective” disorder, a combination of quenched disorder and intrinsic localized spins.

Quasiparticle Properties of a Mobile Impurity in a Bose-Einstein Condensate.

Science.gov (United States)

Christensen, Rasmus Søgaard; Levinsen, Jesper; Bruun, Georg M

2015-10-16

We develop a systematic perturbation theory for the quasiparticle properties of a single impurity immersed in a Bose-Einstein condensate. Analytical results are derived for the impurity energy, effective mass, and residue to third order in the impurity-boson scattering length. The energy is shown to depend logarithmically on the scattering length to third order, whereas the residue and the effective mass are given by analytical power series. When the boson-boson scattering length equals the boson-impurity scattering length, the energy has the same structure as that of a weakly interacting Bose gas, including terms of the Lee-Huang-Yang and fourth order logarithmic form. Our results, which cannot be obtained within the canonical Fröhlich model of an impurity interacting with phonons, provide valuable benchmarks for many-body theories and for experiments.

Dark matter as the Bose-Einstein condensation in loop quantum cosmology

International Nuclear Information System (INIS)

Atazadeh, K.; Mousavi, M.; Darabi, F.

2016-01-01

We consider the FLRW universe in a loop quantum cosmological model filled with radiation, baryonic matter (with negligible pressure), dark energy, and dark matter. The dark matter sector is supposed to be of Bose-Einstein condensate type. The Bose-Einstein condensation process in a cosmological context by supposing it as an approximate first-order phase transition, has already been studied in the literature. Here, we study the evolution of the physical quantities related to the early universe description such as the energy density, temperature, and scale factor of the universe, before, during, and after the condensation process. We also consider in detail the evolution era of the universe in a mixed normal-condensate dark matter phase. The behavior and time evolution of the condensate dark matter fraction is also analyzed. (orig.)

Role of superconducting energy gap in extended BCS-Bose crossover theory

Science.gov (United States)

Chávez, I.; García, L. A.; de Llano, M.; Grether, M.

2017-10-01

The generalized Bose-Einstein condensation (GBEC) theory of superconductivity (SC) is briefly surveyed. It hinges on three distinct new ingredients: (i) Treatment of Cooper pairs (CPs) as actual bosons since they obey Bose statistics, in contrast to BCS pairs which do not obey Bose commutation relations; (ii) inclusion of two-hole Cooper pairs (2hCPs) on an equal footing with two-electron Cooper pairs (2eCPs), thus making this a complete boson-fermion (BF) model; and (iii) inclusion in the resulting ternary ideal BF gas with particular BF vertex interactions that drive boson formation/disintegration processes. GBEC subsumes as special cases both BCS (having its 50-50 symmetry of both kinds of CPs) and ordinary BEC theories (having no 2hCPs), as well as the now familiar BCS-Bose crossover theory. We extended the crossover theory with the explicit inclusion of 2hCPs and construct a phase diagram of Tc/TF versus n/nf, where Tc and TF are the critical and Fermi temperatures, n is the total number density and nf that of unbound electrons at T = 0. Also, with this extended crossover one can construct the energy gap Δ(T)/Δ(0) versus T/Tc for some elemental SCs by solving at least two equations numerically: a gap-like and a number equation. In 50-50 symmetry, the energy gap curve agrees quite well with experimental data. But ignoring 2hCPs altogether leads to the gap curve falling substantially below that with 50-50 symmetry which already fits the data quite well, showing that 2hCPs are indispensable to describe SCs.

On the occurrence and detectability of Bose-Einstein condensation in helium white dwarfs

International Nuclear Information System (INIS)

Benvenuto, O.G.; Vito, M.A. De

2011-01-01

It has been recently proposed that helium white dwarfs may provide promising conditions for the occurrence of the Bose-Einstein condensation. The argument supporting this expectation is that in some conditions attained in the core of these objects, the typical De Broglie wavelength associated with helium nuclei is of the order of the mean distance between neighboring nuclei. In these conditions the system should depart from classical behavior showing quantum effects. As helium nuclei are bosons, they are expected to condense. In order to explore the possibility of detecting the Bose-Einstein condensation in the evolution of helium white dwarfs we have computed a set of models for a variety of stellar masses and values of the condensation temperature. We do not perform a detailed treatment of the condensation process but mimic it by suppressing the nuclei contribution to the equation of state by applying an adequate function. As the cooling of white dwarfs depends on average properties of the whole stellar interior, this procedure should be suitable for exploring the departure of the cooling process from that predicted by the standard treatment. We find that the Bose-Einstein condensation has noticeable, but not dramatic effects on the cooling process only for the most massive white dwarfs compatible with a helium dominated interior ( ≈ 0.50M s un) and very low luminosities (say, Log(L/L s un) < −4.0). These facts lead us to conclude that it seems extremely difficult to find observable signals of the Bose-Einstein condensation. Recently, it has been suggested that the population of helium white dwarfs detected in the globular cluster NGC 6397 is a good candidate for detecting signals of the Bose-Einstein condensation. We find that these stars have masses too low and are too bright to have an already condensed interior

Hole motion in the t-J and Hubbard models: Effect of a next-nearest-neighbor hopping

International Nuclear Information System (INIS)

Gagliano, E.; Bacci, S.; Dagotto, E.

1990-01-01

Using exact diagonalization techniques, we study one dynamical hole in the two-dimensional t-J and Hubbard models on a square lattice including a next-nearest-neighbor hopping t'. We present the phase diagram in the parameter space (J/t,t'/t), discussing the ground-state properties of the hole. At J=0, a crossing of levels exists at some value of t' separating a ferromagnetic from an antiferromagnetic ground state. For nonzero J, at least four different regions appear where the system behaves like an antiferromagnet or a (not fully saturated) ferromagnet. We study the quasiparticle behavior of the hole, showing that for small values of |t'| the previously presented string picture is still valid. We also find that, for a realistic set of parameters derived from the Cu-O Hamiltonian, the hole has momentum (π/2,π/2), suggesting an enhancement of the p-wave superconducting mode due to the second-neighbor interactions in the spin-bag picture. Results for the t-t'-U model are also discussed with conclusions similar to those of the t-t'-J model. In general we found that t'=0 is not a singular point of these models

Bose, Prof. Satyendra Nath

Indian Academy of Sciences (India)

Home; Fellowship. Fellow Profile. Elected: 1973 Honorary. Bose, Prof. Satyendra Nath. Date of birth: 1 January 1894. Date of death: 4 February 1974. YouTube; Twitter; Facebook; Blog. Academy News. IAS Logo. 29th Mid-year meeting. Posted on 19 January 2018. The 29th Mid-year meeting of the Academy will be held ...

Characteristics of the Mott transition and electronic states of high-temperature cuprate superconductors from the perspective of the Hubbard model

Science.gov (United States)

Kohno, Masanori

2018-04-01

A fundamental issue of the Mott transition is how electrons behaving as single particles carrying spin and charge in a metal change into those exhibiting separated spin and charge excitations (low-energy spin excitation and high-energy charge excitation) in a Mott insulator. This issue has attracted considerable attention particularly in relation to high-temperature cuprate superconductors, which exhibit electronic states near the Mott transition that are difficult to explain in conventional pictures. Here, from a new viewpoint of the Mott transition based on analyses of the Hubbard model, we review anomalous features observed in high-temperature cuprate superconductors near the Mott transition.

Bose-Einstein condensation of photons in an optical microcavity

OpenAIRE

Klaers, Jan; Schmitt, Julian; Vewinger, Frank; Weitz, Martin

2010-01-01

Bose-Einstein condensation, the macroscopic ground state accumulation of particles with integer spin (bosons) at low temperature and high density, has been observed in several physical systems, including cold atomic gases and solid state physics quasiparticles. However, the most omnipresent Bose gas, blackbody radiation (radiation in thermal equilibrium with the cavity walls) does not show this phase transition, because the chemical potential of photons vanishes and, when the temperature is r...

Quantum statistics measurements using 2-, 3- and 4-pion Bose-Einstein correlations

CERN Multimedia

CERN. Geneva

2014-01-01

We also present measurements of the source radii with 3-pion Bose-Einstein cumulants in pp, p-Pb, and Pb-Pb collisions. The resulting comparisons of the radii in all three systems at similar multiplicity has implications on the hydrodynamic modeling of high-energy collisions.

Mean-field results of the multiple-band extended Hubbard model for the square-planar CuO2 lattice

International Nuclear Information System (INIS)

Nimkar, S.; Sarma, D.D.; Krishnamurthy, H.R.; Ramasesha, S.

1993-01-01

We obtain metal-insulator phase diagrams at half-filling for the five-band extended Hubbard model of the square-planar CuO 2 lattice treated within a Hartree-Fock mean-field approximation, allowing for spiral spin-density waves. We indicate the existence of an insulating phase (covalent insulator) characterized by strong covalency effects, not identified in the earlier Zaanen-Sawatzky-Allen phase diagram. While the insulating phase is always antiferromagnetic, we also obtain an antiferromagnetic metallic phase for a certain range of interaction parameters. Performing a nonperturbative calculation of J eff , the in-plane antiferromagnetic interaction is presented as a function of the parameters in the model. We also calculate the band gap and magnetic moments at various sites and discuss critically the contrasting interpretation of the electronic structure of high-T c materials arising from photoemission and neutron-scattering experiments

Bose-Operator Expansions of Tensor Operators in the Theory of Magnetism

DEFF Research Database (Denmark)

Lindgård, Per-Anker; Danielsen, O.

1974-01-01

Using a method of matching corresponding matrix elements, a hermitian Bose-operator expansion of tensor operators of arbitrary rank which transforms all kinematic effects into dynamical interactions between Bose particles is derived. It is shown that the method is a generalization of the Holstein...

Bose-Einstein correlations between kaons

International Nuclear Information System (INIS)

Akesson, T.; Batley, R.; Breuker, H.; Dam, P.; Eidelman, S.; Fabian, C.W.; Frandsen, P.; Goerlach, U.; Heck, B.; Hilke, H.J.; Jeffreys, P.; Kalinovsky, A.; Kesseler, G.; Lans, J. van der; Lindsay, J.; Markou, A.; Mjoernmark, U.; Nielsen, B.S.; Olsen, L.H.; Rosselet, L.; Rosso, E.; Rudge, A.; Schindler, R.; Willis, W.J.; Witzeling, W.; Albrow, M.G.; Cockerill, D.; Evans, W.M.; Gibson, M.; Hiddleston, J.; MacCubbin, N.A.; Williamson, J.; Benary, O.; Dagan, S.; Lissauer, D.; Oren, Y.; Boeggild, H.; Botner, O.; Dahl-Jensen, E.; Dahl-Jensen, I.; Damgaard, G.; Hansen, K.H.; Hooper, J.; Moeller, R.; Brody, H.; Frankel, S.; Frati, W.; Molzon, W.; Vella, E.; Zajc, W.A.; Burkert, V.; Carter, J.R.; Cecil, P.; Chung, S.U.; Gordon, H.; Ludlam, T.; Winik, M.; Woody, C.; Cleland, W.E.; Kroeger, R.; Sullivan, M.; Thompson, J.A.

1985-01-01

Bose-Einstein correlations between identical charged kaons are observed in αα, pp, and panti p collisions at the CERN Intersecting Storage Rings. The average radial extension of the K-emitting region is found to be (2.4+-0.9) fm. (orig.)

Mapping the electron correlation onto a model Hamiltonian for Cs/GaAs(110): a Mott-Hubbard insulator at quarter filling

CERN Document Server

Chen Chang Feng

1998-01-01

We have constructed an effective model Hamiltonian in the Hubbard formalism for the Cs/GaAs(110) surface at quarter-monolayer coverage with all of the parameters extracted from constrained local-density-approximation (LDA) pseudopotential calculations. The single-particle excitation spectrum of the model has been calculated using an exact-diagonalization technique to help determine the relevant interaction terms. It is shown that the intersite interaction between the nearest-neighbour Ga sites plays the key role in determining the insulating nature of the system and must be included in the model, in contrast to suggestions of some previous work. Our results show that a reliable mapping of LDA results onto an effective model Hamiltonian can be achieved by combining constrained LDA calculations for the Hamiltonian parameters and many-body calculations of the single-particle excitation spectrum for identifying relevant interaction terms. (author)

Effects of geometrical frustration on ferromagnetism in the Hubbard model on the generalised Shastry-Sutherland lattice

Science.gov (United States)

Farkašovský, Pavol

2018-05-01

The small-cluster exact-diagonalization calculations and the projector quantum Monte Carlo method are used to examine the competing effects of geometrical frustration and interaction on ferromagnetism in the Hubbard model on the generalised Shastry-Sutherland lattice. It is shown that the geometrical frustration stabilizes the ferromagnetic state at high electron concentrations ( n ≳ 7/4), where strong correlations between ferromagnetism and the shape of the noninteracting density of states are observed. In particular, it is found that ferromagnetism is stabilized for these values of frustration parameters, which lead to the single-peaked noninterating density of states at the band edge. Once, two or more peaks appear in the noninteracting density of states at the band edge the ferromagnetic state is suppressed. This opens a new route towards the understanding of ferromagnetism in strongly correlated systems.

The Evolution of Hyperedge Cardinalities and Bose-Einstein Condensation in Hypernetworks.

Science.gov (United States)

Guo, Jin-Li; Suo, Qi; Shen, Ai-Zhong; Forrest, Jeffrey

2016-09-27

To depict the complex relationship among nodes and the evolving process of a complex system, a Bose-Einstein hypernetwork is proposed in this paper. Based on two basic evolutionary mechanisms, growth and preference jumping, the distribution of hyperedge cardinalities is studied. The Poisson process theory is used to describe the arrival process of new node batches. And, by using the Poisson process theory and a continuity technique, the hypernetwork is analyzed and the characteristic equation of hyperedge cardinalities is obtained. Additionally, an analytical expression for the stationary average hyperedge cardinality distribution is derived by employing the characteristic equation, from which Bose-Einstein condensation in the hypernetwork is obtained. The theoretical analyses in this paper agree with the conducted numerical simulations. This is the first study on the hyperedge cardinality in hypernetworks, where Bose-Einstein condensation can be regarded as a special case of hypernetworks. Moreover, a condensation degree is also discussed with which Bose-Einstein condensation can be classified.

Improved efficiency of stimulated Raman adiabatic passage in photoassociation of a Bose-Einstein condensate

International Nuclear Information System (INIS)

Mackie, Matt; Suominen, Kalle-Antti; Haerkoenen, Kari; Collin, Anssi; Javanainen, Juha

2004-01-01