43 research outputs found
Test of a Jastrow-type wavefunction for a trapped few-body system in one dimension
For a system with interacting quantum mechanical particles in a
one-dimensional harmonic oscillator, a trial wavefunction with simple structure
based on the solution of the corresponding two-particle system is suggested and
tested numerically. With the inclusion of a scaling parameter for the distance
between particles, at least for the very small systems tested here the ansatz
gives a very good estimate of the ground state energy, with the error being of
the order of ~1% of the gap to the first excited state
Quantum Monte Carlo simulation for the conductance of one-dimensional quantum spin systems
Recently, the stochastic series expansion (SSE) has been proposed as a
powerful MC-method, which allows simulations at low for quantum-spin
systems. We show that the SSE allows to compute the magnetic conductance for
various one-dimensional spin systems without further approximations. We
consider various modifications of the anisotropic Heisenberg chain. We recover
the Kane-Fisher scaling for one impurity in a Luttinger-liquid and study the
influence of non-interacting leads for the conductance of an interacting
system.Comment: 8 pages, 9 figure
Mean-field theory of Bose-Fermi mixtures in optical lattices
We determine the phase diagram of a mixture of ultracold bosons and polarized
fermions placed in an optical lattice using mean field theory. In the limit of
strong atom-atom interactions, there exist quantum phases that involve pairing
of fermions with one or more bosons, or bosonic holes, respectively. We obtain
the analytic form of the phase boundaries separating these composite fermion
phases from the bosonic superfluid coexisting with Fermi liquid. We compare the
results with numerical simulations and discuss their validity and relevance for
current experiments.Comment: 4 pages, 2 eps figures, new section on experimental requirements and
some technical details adde
One-dimensional phase transitions in a two-dimensional optical lattice
A phase transition for bosonic atoms in a two-dimensional anisotropic optical
lattice is considered. If the tunnelling rates in two directions are different,
the system can undergo a transition between a two-dimensional superfluid and a
one-dimensional Mott insulating array of strongly coupled tubes. The connection
to other lattice models is exploited in order to better understand the phase
transition. Critical properties are obtained using quantum Monte Carlo
calculations. These critical properties are related to correlation properties
of the bosons and a criterion for commensurate filling is established.Comment: 14 pages, 8 figure
Dynamical 1/N approach to time-dependent currents through quantum dots
A systematic truncation of the many-body Hilbert space is implemented to
study how electrons in a quantum dot attached to conducting leads respond to
time-dependent biases. The method, which we call the dynamical 1/N approach, is
first tested in the most unfavorable case, the case of spinless fermions (N=1).
We recover the expected behavior, including transient ringing of the current in
response to an abrupt change of bias. We then apply the approach to the
physical case of spinning electrons, N=2, in the Kondo regime for the case of
infinite intradot Coulomb repulsion. In agreement with previous calculations
based on the non-crossing approximation (NCA), we find current oscillations
associated with transitions between Kondo resonances situated at the Fermi
levels of each lead. We show that this behavior persists for a more realistic
model of semiconducting quantum dots in which the Coulomb repulsion is finite.Comment: 18 pages, 7 eps figures, discussion extended for spinless electrons
and typo
Density correlations and dynamical Casimir emission of Bogoliubov phonons in modulated atomic Bose-Einstein condensates
We present a theory of the density correlations that appear in an atomic
Bose-Einstein condensate as a consequence of the dynamical Casimir emission of
pairs of Bogoliubov phonons when the atom-atom scattering length is modulated
in time. Different regimes as a function of the temporal shape of the
modulation are identified and a simple physical picture of the phenomenon is
discussed. Analytical expressions for the density correlation function are
provided for the most significant limiting cases. This theory is able to
explain some unexpected features recently observed in numerical calculations of
Hawking radiation from analog black holes
Quantum Computing and Quantum Simulation with Group-II Atoms
Recent experimental progress in controlling neutral group-II atoms for
optical clocks, and in the production of degenerate gases with group-II atoms
has given rise to novel opportunities to address challenges in quantum
computing and quantum simulation. In these systems, it is possible to encode
qubits in nuclear spin states, which are decoupled from the electronic state in
the S ground state and the long-lived P metastable state on the
clock transition. This leads to quantum computing scenarios where qubits are
stored in long lived nuclear spin states, while electronic states can be
accessed independently, for cooling of the atoms, as well as manipulation and
readout of the qubits. The high nuclear spin in some fermionic isotopes also
offers opportunities for the encoding of multiple qubits on a single atom, as
well as providing an opportunity for studying many-body physics in systems with
a high spin symmetry. Here we review recent experimental and theoretical
progress in these areas, and summarise the advantages and challenges for
quantum computing and quantum simulation with group-II atoms.Comment: 11 pages, 7 figures, review for special issue of "Quantum Information
Processing" on "Quantum Information with Neutral Particles
Dynamic correlation functions in one-dimensional quasi-condensates
We calculate the static and dynamic single-particle correlation functions in
one-dimensional (1D) trapped Bose gases and discuss experimental measurements
that can directly probe such correlation functions. Using a quantized
hydrodynamic theory for the low energy excitations, we calculate both the
static and dynamic single-particle correlation functions for a 1D Bose gas that
is a phase-fluctuating quasi-condensate. For the static (equal-time)
correlation function, our approximations and results are equivalent to those of
Petrov, Shlyapnikov and Walraven. The Fourier transform of the static
single-particle correlation function gives the momentum distribution, which can
be measured using Doppler-sensitive Bragg scattering experiments on a highly
elongated Bose gas. We show how a two-photon Raman out-coupling experiment can
measure the characteristic features of the dynamic or time-dependent
single-particle correlation function of a 1D Bose quasi-condensate.Comment: 19 pages, 4 figures; submitted to Phys. Rev.
Kondo effect in coupled quantum dots: a Non-crossing approximation study
The out-of-equilibrium transport properties of a double quantum dot system in
the Kondo regime are studied theoretically by means of a two-impurity Anderson
Hamiltonian with inter-impurity hopping. The Hamiltonian, formulated in
slave-boson language, is solved by means of a generalization of the
non-crossing approximation (NCA) to the present problem. We provide benchmark
calculations of the predictions of the NCA for the linear and nonlinear
transport properties of coupled quantum dots in the Kondo regime. We give a
series of predictions that can be observed experimentally in linear and
nonlinear transport measurements through coupled quantum dots. Importantly, it
is demonstrated that measurements of the differential conductance , for the appropriate values of voltages and inter-dot tunneling
couplings, can give a direct observation of the coherent superposition between
the many-body Kondo states of each dot. This coherence can be also detected in
the linear transport through the system: the curve linear conductance vs
temperature is non-monotonic, with a maximum at a temperature
characterizing quantum coherence between both Kondo states.Comment: 20 pages, 17 figure
Easy-axis ferromagnetic chain on a metallic surface
10.1088/0953-8984/25/9/094008Journal of Physics Condensed Matter259-JCOM