149 research outputs found
Many-Body Entanglement in Short-Range Interacting Fermi Gases for Metrology
We explore many-body entanglement in spinful Fermi gases with short-range
interactions, for metrology purposes. We characterize the emerging quantum
phases via Density-Matrix Renormalization Group simulations and quantify their
entanglement content for metrological usability via the Quantum Fisher
Information (QFI). Our study establishes a method, promoting the QFI to be an
order parameter. Short-range interactions reveal to build up metrologically
promising entanglement in the XY-ferromagnetic and cluster ordering, the
cluster physics being unexplored so far.Comment: 5 pages, 4 figures + 10 pages, 8 figures of supplementa
Screening effects in bipolaron theory and high temperature superconductivity
The subject of the book is a study on bipolaron formation in heavily doped and polar materials. The study is applied to the physics of superconducting compounds with high transition temperature
Correlation Length and Universality in the BCS-BEC Crossover for Energy-Dependent Resonance Superfluidity
We consider the BCS-BEC crossover of a quantum Fermi
gas at T = 0 in the presence of an energy-dependent Fano-Feshbach
resonance, driving the system from broad to narrow limits.We choose a
minimal microscopic potential reproducing the two-particle resonance
physics in terms of the scattering length a and the eective range
R representing the resonance width, and solve the BCS mean-eld
equations varying a, R and the density. We show that the chemical
potential and the condensate fraction manifest an universal behavior
when the correlation length, measuring the pair size, is used as the
crossover parameter. These results can be useful in view of the more
recent perspectives of realizing narrow resonances also by optical means
and amenable as a base Quantum Monte Carlo simulations
Probing the energy bands of a Bose-Einstein condensate in an optical lattice
We simulate several methods which could be realized in the laboratory to probe the band excitation energies and the momentum distribution of a Bose-Einstein condensate inside an optical lattice. The values of the excitation energies obtained by the different methods agree within the accuracy of the simulation. The meaning of the results in terms of density and phase deformations is tested by studying the relaxation of a phase-modulated condensate toward the ground state
Incommensurate phases of a bosonic two-leg ladder under a flux
A boson two--leg ladder in the presence of a synthetic magnetic flux is
investigated by means of bosonization techniques and Density Matrix
Renormalization Group (DMRG). We follow the quantum phase transition from the
commensurate Meissner to the incommensurate vortex phase with increasing flux
at different fillings. When the applied flux is and close to it,
where is the filling per rung, we find a second incommensuration in the
vortex state that affects physical observables such as the momentum
distribution, the rung-rung correlation function and the spin-spin and
charge-charge static structure factors.Comment: 19 pages, 9 EPS figures, RevTeX 4 (v1); 20 pages, 10 EPS figures,
improved section on mean-field theory (v2
Ground state of trapped interacting Bose-Einstein condensates by an explicit imaginary-time algorithm
We show that an explicit time-marching method previously developed for the numerical study of the dynamics of Bose-Einstein condensates can be profitably adapted to the numerical determination of their ground state. After reduction to a one-dimensional model, we first reproduce and test known results on condensates in harmonic traps and then determine the ground state of a condensate in a harmonically bound optical lattice in the range of parameters which are relevant to existing experiments
Persisting Meissner state and incommensurate phases of hard-core boson ladders in a flux
The phase diagram of a half-filled hard core boson two-leg ladder in a flux
is investigated by means of numerical simulations based on the Density Matrix
Renormalization Group (DMRG) algorithm and bosonization. We calculate
experimentally accessible observables such as the momentum distribution, as
well as rung current, density wave and bond-order wave correlation functions,
allowing us to identify the Mott Meissner and Mott Vortex states. We follow the
transition from commensurate Meissner to incommensurate Vortex state at
increasing interchain hopping till the critical value [Piraud et al. Phys. Rev.
B v. 91, p. 140406 (2015)] above which the Meissner state is stable at any
flux. For flux close to , and below the critical hopping, we observe the
formation of a second incommensuration in the Mott Vortex state that could be
detectable in current experiments.Comment: RevTeX 4, 5 pages + 8 pages supplemental, 6 EPS figures; (v2)
references added, corrected the discussion of the Meissner state at high
interchain hoppin
Quantum Effects in the Aubry Transition
The Aubry transition between sliding and pinned phases, driven by the
competition between two incommensurate length scales, represents a paradigm
that is applicable to a large variety of microscopically distinct systems.
Despite previous theoretical studies, it remains an open question to what
extent quantum effects modify the transition, or are experimentally observable.
An experimental platform that can potentially reach the quantum regime has
recently become available in the form of trapped laser-cooled ions subject to a
periodic optical potential [A. Bylinskii, D. Gangloff, I. Counts, and V.
Vuletic, Nature Materials 15, 717 (2016)]. Using Path-Integral Monte Carlo
(PIMC) simulation methods, we analyze the impact of quantum tunneling on the
sliding-to-pinned transition in this system, and determine the phase diagram in
terms of incommensuration and potential strength. We propose new signatures of
the quantum Aubry transition that are robust against thermal and finite-size
effects, and that can be observed in future experiments.Comment: 10 pages, 7 figure
Hydrodynamic excitations in a spin-polarized Fermi gas under harmonic confinement in one dimension
We consider a time-dependent nonlinear Schrodinger equation in one dimension (1D) with a fifth-order interaction term and external harmonic confinement, as a model for both (i) a Bose gas with hard-core contact interactions in the local-density approximation, and (ii) a spin-polarized Fermi gas in the collisional regime. We evaluate analytically in the Thomas-Fermi limit the density fluctuation profiles and the collective excitation frequencies, and compare the results for the low-lying modes with those obtained from numerical solution of the Schrodinger equation. We find that the excitation frequencies are multiples of the harmonic-trap frequency even in the strong-coupling Thomas-Fermi regime. This result shows that the hydrodynamic and the collisionless collective spectra coincide in the harmonically confined 1D Fermi gas, as they do for sound waves in its homogeneous analog. It also shows that in this case the local-density theory reproduces the exact collective spectrum of the hard-core Bose gas under harmonic confinement
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