703 research outputs found
New Family of Solvable 1D Heisenberg Models
Starting from a Calogero--Sutherland model with hyperbolic interaction
confined by an external field with Morse potential we construct a Heisenberg
spin chain with exchange interaction on a lattice given
in terms of the zeroes of Laguerre polynomials. Varying the strength of the
Morse potential the Haldane--Shastry and harmonic spin chains are reproduced.
The spectrum of the models in this class is found to be that of a classical
one-dimensional Ising chain with nonuniform nearest neighbour coupling in a
nonuniform magnetic field which allows to study the thermodynamics in the limit
of infinite chains.Comment: 8 pp, LaTeX, ITP-UH-07/9
Phase diagram of an exactly solvable t-J ladder model
We study a system of one-dimensional t-J models coupled to a ladder system. A
special choice of the interaction between neighbouring rungs leads to an
integrable model with supersymmetry, which is broken by the presence of rung
interactions. We analyze the spectrum of low-lying excitations and ground state
phase diagram at zero temperature.Comment: LaTeX, 8 pp. incl. 1 figur
Theory of quasi-one dimensional imbalanced Fermi gases
We present a theory for a lattice array of weakly coupled one-dimensional
ultracold attractive Fermi gases (1D `tubes') with spin imbalance, where strong
intratube quantum fluctuations invalidate mean field theory. We first construct
an effective field theory, which treats spin-charge mixing exactly, based on
the Bethe ansatz solution of the 1D single tube problem. We show that the 1D
Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) state is a two-component Luttinger
liquid, and its elementary excitations are fractional states carrying both
charge and spin. We analyze the instability of the 1D FFLO state against
inter-tube tunneling by renormalization group analysis, and find that it flows
into either a polarized Fermi liquid or a FFLO superfluid, depending on the
magnitude of interaction strength and spin imbalance. We obtain the phase
diagram of the quasi-1D system and further determine the scaling of the
superfluid transition temperature with intertube coupling.Comment: new expanded version, 8 pages, updated reference
Emergence of Quantum Ergodicity in Rough Billiards
By analytical mapping of the eigenvalue problem in rough billiards on to a
band random matrix model a new regime of Wigner ergodicity is found. There the
eigenstates are extended over the whole energy surface but have a strongly
peaked structure. The results of numerical simulations and implications for
level statistics are also discussed.Comment: revtex, 4 pages, 4 figure
Properties of the chiral spin liquid state in generalized spin ladders
We study zero temperature properties of a system of two coupled quantum spin
chains subject to fields explicitly breaking time reversal symmetry and parity.
Suitable choice of the strength of these fields gives a model soluble by Bethe
Ansatz methods which allows to determine the complete magnetic phase diagram of
the system and the asymptotics of correlation functions from the finite size
spectrum. The chiral properties of the system for both the integrable and the
nonintegrable case are studied using numerical techniques.Comment: 19 pages, 9eps figures, Late
The FFLO state in the one-dimensional attractive Hubbard model and its fingerprint in the spatial noise correlations
We explore the pairing properties of the one-dimensional attractive Hubbard
model in the presence of finite spin polarization. The correlation exponents
for the most important fluctuations are determined as a function of the density
and the polarization. We find that in a system with spin population imbalance,
Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-type pairing at wavevector
Q=|k_{F,\uparrow}-k_{F,\downarrow}| is always dominant and there is no
Chandrasekhar-Clogston limit. We then investigate the case of weakly coupled 1D
systems and determine the region of stability of the 1D FFLO phase. This
picture is corroborated by density-matrix-renormalization-group (DMRG)
simulations of the spatial noise correlations in uniform and trapped systems,
unambiguously revealing the presence of fermion pairs with nonzero momentum Q.
This opens up an interesting possibility for experimental studies of FFLO
states.Comment: 8 pages, 4 figure
Open t-J chain with boundary impurities
We study integrable boundary conditions for the supersymmetric t-J model of
correlated electrons which arise when combining static scattering potentials
with dynamical impurities carrying an internal degree of freedom. The latter
differ from the bulk sites by allowing for double occupation of the local
orbitals. The spectrum of the resulting Hamiltonians is obtained by means of
the algebraic Bethe Ansatz.Comment: LaTeX2e, 9p
Quantum phase estimation algorithm in presence of static imperfections
We study numerically the effects of static imperfections and residual
couplings between qubits for the quantum phase estimation algorithm with two
qubits. We show that the success probability of the algorithm is affected
significantly more by static imperfections than by random noise errors in
quantum gates. An improvement of the algorithm accuracy can be reached by
application of the Pauli-random-error-correction method (PAREC).Comment: 5 pages, 5 figures. Research avilable at
http://www.quantware.ups-tlse.fr
Spectrum of boundary states in the open Hubbard chain
We use the Bethe Ansatz solution for the one dimensional Hubbard model with
open boundary conditions and applied boundary fields to study the spectrum of
bound states at the boundary. Depending on the strength of the boundary
potentials one finds that the true ground state contains a single charge or,
for boundary potentials comparable to the Hubbard interaction, a pair of
electrons in a bound state. If these are left unoccupied one finds holon and
spinon bound states. We compute the finite size corrections to the low lying
energies in this system and use the predictions of boundary conformal field
theory to study the exponents related to the orthogonality catastrophe.Comment: LaTeX + epsf,amssymb macros, 14 pp. incl. figure
The D 3 2 spin chain and its finite-size spectrum
Using the analytic Bethe ansatz, we initiate a study of the scaling limit of the quasi-periodic D32 spin chain. Supported by a detailed symmetry analysis, we determine the effective scaling dimensions of a large class of states in the parameter regime γ ∈ (0, π4). Besides two compact degrees of freedom, we identify two independent continuous components in the finite-size spectrum. The influence of large twist angles on the latter reveals also the presence of discrete states. This allows for a conjecture on the central charge of the conformal field theory describing the scaling limit of the lattice model
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