1,195 research outputs found
Quantum Numbers for Excitations of Bose-Einstein Condensates in 1D Optical Lattices
The excitation spectrum and the band structure of a Bose-Einstein condensate
in a periodic potential are investigated. Analyses within full 3D systems,
finite 1D systems, and ideal periodic 1D systems are compared. We find two
branches of excitations in the spectra of the finite 1D model. The band
structures for the first and (part of) the second band are compared between a
finite 1D and the fully periodic 1D systems, utilizing a new definition of a
effective wavenumber and a phase-slip number. The upper and lower edges of the
first gap coincide well between the two cases. The remaining difference is
explained by the existence of the two branches due to the finite-size effect.Comment: 5 pages, 9 figure
Stability of the Haldane phase in anisotropic magnetic ladders
We have considered the properties of anisotropic two-leg ladder models with
S=1/2 or S=1 spins on the rungs, using White's density matrix renormalization
group method. We have generalized the method by taking into account the
symmetries of the model in order to reduce the dimensions of the matrix to be
diagonalized, thereby making possible to consider more states. The boundaries
in the parameter space of the extended region, where the Haldane phase exists,
are estimated.Comment: 19 pages, 5 figure
Kondo Insulators Modeled by the One Dimensional Anderson Lattice: A Numerical Renormalization Group Study
In order to better understand Kondo insulators, we have studied both the
symmetric and asymmetric Anderson lattices at half-filling in one dimension
using the density matrix formulation of the numerical renormalization group. We
have calculated the charge gap, spin gap and quasiparticle gap as a function of
the repulsive interaction U using open boundary conditions for lattices as
large as 24 sites. We find that the charge gap is larger than the spin gap for
all U for both the symmetric and asymmetric cases. RKKY interactions are
evident in the f-spin-f-spin correlation functions at large U in the symmetric
case, but are suppressed in the asymmetric case as the f-level approaches the
Fermi energy. This suppression can also be seen in the staggered susceptibility
and it is consistent with neutron scattering measurements in CeNiSn.Comment: 32 pages, Latex file with Postcript figures
Impact of germline DNA repair gene variants on prognosis and treatment of men with advanced prostate cancer.
The clinical importance of germline variants in DNA repair genes (DRGs) is becoming increasingly recognized, but their impact on advanced prostate cancer prognosis remains unclear. A cohort of 221 newly diagnosed metastatic castration-resistant prostate cancer (mCRPC) patients were screened for pathogenic germline variants in 114 DRGs. The primary endpoint was progression-free survival (PFS) on first-line androgen signaling inhibitor (ARSI) treatment for mCRPC. Secondary endpoints were time to mCRPC progression on initial androgen deprivation therapy (ADT) and overall survival (OS). Twenty-seven patients (12.2%) carried a germline DRG variant. DRG carrier status was independently associated with shorter PFS on first-line ARSI [HR 1.72 (1.06-2.81), P = 0.029]. At initiation of ADT, DRG carrier status was independently associated with shorter progression time to mCRPC [HR 1.56, (1.02-2.39), P = 0.04] and shorter OS [HR 1.99, (1.12-3.52), P = 0.02]. Investigating the contributions of individual germline DRG variants on PFS and OS revealed CHEK2 variants to have little effect. Furthermore, prior taxane treatment was associated with worse PFS on first-line ARSI for DRG carriers excluding CHEK2 (P = 0.0001), but not for noncarriers. In conclusion, germline DRG carrier status holds independent prognostic value for predicting advanced prostate cancer patient outcomes and may potentially inform on optimal treatment sequencing already at the hormone-sensitive stage
Narrowband frequency tunable light source of continuous quadrature entanglement
We report the observation of non-classical quantum correlations of continuous
light variables from a novel type of source. It is a frequency non-degenerate
optical parametric oscillator below threshold, where signal and idler fields
are separated by 740MHz corresponding to two free spectrum ranges of the
parametric oscillator cavity. The degree of entanglement observed, - 3.8 dB, is
the highest to-date for a narrowband tunable source suitable for atomic quantum
memory and other applications in atomic physics. Finally we use the latter to
visualize the Einstein-Podolsky-Rosen paradox.Comment: 11 pages, 9 figures, LaTe
Transmittivity of a Bose-Einstein condensate on a lattice: interference from period doubling and the effect of disorder
We evaluate the particle current flowing in steady state through a
Bose-Einstein condensate subject to a constant force in a quasi-onedimensional
lattice and to attractive interactions from fermionic atoms that are localized
in various configurations inside the lattice wells. The system is treated
within a Bose-Hubbard tight binding model by an out-of-equilibrium Green's
function approach. A new band gap opens up when the lattice period is doubled
by locating the fermions in alternate wells and yields an interference pattern
in the transmittivity on varying the intensity of the driving force. The
positions of the transmittivity minima are determined by matching the period of
Bloch oscillations and the time for tunnelling across the band gap. Massive
disorder in the distribution of the fermions will wash out the interference
pattern, but the same period doubling of the lattice can be experimentally
realized in a four-beam set-up. We report illustrative numerical results for a
mixture of 87Rb and 40K atoms in an optical lattice created by laser beams with
a wavelength of 763 nm.Comment: 13 pages, 5 figure
A density matrix renormalisation group algorithm for quantum lattice systems with a large number of states per site
A variant of White's density matrix renormalisation group scheme which is
designed to compute low-lying energies of one-dimensional quantum lattice
models with a large number of degrees of freedom per site is described. The
method is tested on two exactly solvable models---the spin-1/2
antiferromagnetic Heisenberg chain and a dimerised XY spin chain. To illustrate
the potential of the method, it is applied to a model of spins interacting with
quantum phonons. It is shown that the method accurately resolves a number of
energy gaps on periodic rings which are sufficiently large to afford an
accurate investigation of critical properties via the use of finite-size
scaling theory.Comment: RevTeX, 8 pages, 2 figure
The density-matrix renormalization group
The density-matrix renormalization group (DMRG) is a numerical algorithm for
the efficient truncation of the Hilbert space of low-dimensional strongly
correlated quantum systems based on a rather general decimation prescription.
This algorithm has achieved unprecedented precision in the description of
one-dimensional quantum systems. It has therefore quickly acquired the status
of method of choice for numerical studies of one-dimensional quantum systems.
Its applications to the calculation of static, dynamic and thermodynamic
quantities in such systems are reviewed. The potential of DMRG applications in
the fields of two-dimensional quantum systems, quantum chemistry,
three-dimensional small grains, nuclear physics, equilibrium and
non-equilibrium statistical physics, and time-dependent phenomena is discussed.
This review also considers the theoretical foundations of the method, examining
its relationship to matrix-product states and the quantum information content
of the density matrices generated by DMRG.Comment: accepted by Rev. Mod. Phys. in July 2004; scheduled to appear in the
January 2005 issu
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