44 research outputs found
The excitonic collapse of higher Landau level fractional quantum Hall effect
The scarcity of the fractional quantum Hall effect in higher Landau levels is
a most intriguing fact when contrasted with its great abundance in the lowest
Landau level. This paper shows that a suppression of the hard core repulsion in
going from the lowest Landau level to higher Landau levels leads to a collapse
of the energy of the neutral excitation, destabilizing all fractional states in
the third and higher Landau levels, and almost all in the second Landau level.
The remaining fractions are in agreement with those observed experimentally.Comment: 5 pages, 3 figures. To appear in Phys. Rev. B Rapid Communicatio
Possible Pairing-Induced Even-Denominator Fractional Quantum Hall Effect in the Lowest Landau Level
We report on our theoretical investigations that point to the possibility of
a fractional quantum Hall effect with partial spin polarization at .
The physics of the incompressible state proposed here involves p-wave pairing
of composite fermions in the spin reversed sector. The temperature and magnetic
field regimes for the realization of this state are estimated
Nonlocal electrodynamics of two-dimensional wire mesh photonic crystals
We calculate analytically the spectra of plasma waves and electromagnetic
waves (EMW) in metallic photonic crystal consisting of the parallel thin
infinite metallic cylinders embedded in the dielectric media. The axes of
metallic cylinders form a regular square lattice in a plane perpendicular to
them. The metal inside the cylinders is assumed to be in the high frequency
regime , where is the relaxation time. The proposed
analytical theory is based upon small parameters , where is the
volume fraction of the metal, and , where is the wave vector and
is the radius of the cylinder. It is shown that there are five different
branches of the EMW that cover all frequency range under consideration except
one very small omnidirectional gap in the vicinity of the frequency of the
surface plasmon. However, at some directions of propagation and polarizations
the gap may be much larger. The reflection and refraction of the EMW is also
considered. The general theory of refraction is proposed which is complicated
by the spatial dispersion of the dielectric constant, and one particular
geometry of the incident EMW is considered.Comment: 14 pages, 8 figure
Pseudospin and Quantum Computation in Semiconductor Nanostructures
We review the theoretical aspects of pseudospin quantum computation using
vertically coupled quantum dots in the quantum Hall regime. We discuss the
robustness and addressability of these collective, charge-based qubits. The low
energy Hilbert space of a coupled set of qubits yields an effective quantum
Ising model tunable through external gates. An experimental prediction of an
even-odd effect in the Coulomb blockade spectra of the coupled quantum dot
system probes the parameter regime necessary for realization of these qubits.Comment: 13 pages, 6 figures, New Journal of Physics Focus Issue on "Solid
State Quantum Information
Two-Roton Bound State in the Fractional Quantum Hall Effect
The true nature of the lowest-energy, long-wavelength neutral excitation of
the fractional quantum Hall effect has been a long outstanding problem. In this
Letter, we establish that it is a two-roton bound state.Comment: 4 pages, 4 figures; Physical Review Letters, in pres
Macroscopic superposition states of ultracold bosons in a double-well potential
We present a thorough description of the physical regimes for ultracold
bosons in double wells, with special attention paid to macroscopic
superpositions (MSs). We use a generalization of the Lipkin-Meshkov-Glick
Hamiltonian of up to eight single particle modes to study these MSs, solving
the Hamiltonian with a combination of numerical exact diagonalization and
high-order perturbation theory. The MS is between left and right potential
wells; the extreme case with all atoms simultaneously located in both wells and
in only two modes is the famous NOON state, but our approach encompasses much
more general MSs. Use of more single particle modes brings dimensionality into
the problem, allows us to set hard limits on the use of the original two-mode
LMG model commonly treated in the literature, and also introduces a new mixed
Josephson-Fock regime. Higher modes introduce angular degrees of freedom and MS
states with different angular properties.Comment: 15 pages, 8 figures, 1 table. Mini-review prepared for the special
issue of Frontiers of Physics "Recent Progresses on Quantum Dynamics of
Ultracold Atoms and Future Quantum Technologies", edited by Profs. Lee, Ueda,
and Drummon
Variational Monte Carlo analysis of the Hubbard model with a confining potential: one-dimensional fermionic optical lattice systems
We investigate the one-dimensional Hubbard model with a confining potential,
which may describe cold fermionic atoms trapped in an optical lattice.
Combining the variational Monte Carlo simulations with the new stochastic
reconfiguration scheme proposed by Sorella, we present an efficient method to
systematically treat the ground state properties of the confined system with a
site-dependent potential. By taking into account intersite correlations as well
as site-dependent on-site correlations, we are able to describe the coexistence
of the metallic and Mott insulating regions, which is consistent with other
numerical results. Several possible improvements of the trial states are also
addressed.Comment: 7 pages, 15 figures; removed unnecessary graphs (p.8-p.32 in the old
version are removed
Ultracold atomic gases in optical lattices: mimicking condensed matter physics and beyond
We review recent developments in the physics of ultracold atomic and
molecular gases in optical lattices. Such systems are nearly perfect
realisations of various kinds of Hubbard models, and as such may very well
serve to mimic condensed matter phenomena. We show how these systems may be
employed as quantum simulators to answer some challenging open questions of
condensed matter, and even high energy physics. After a short presentation of
the models and the methods of treatment of such systems, we discuss in detail,
which challenges of condensed matter physics can be addressed with (i)
disordered ultracold lattice gases, (ii) frustrated ultracold gases, (iii)
spinor lattice gases, (iv) lattice gases in "artificial" magnetic fields, and,
last but not least, (v) quantum information processing in lattice gases. For
completeness, also some recent progress related to the above topics with
trapped cold gases will be discussed.Comment: Review article. v2: published version, 135 pages, 34 figure
The ALPS project release 2.0: Open source software for strongly correlated systems
We present release 2.0 of the ALPS (Algorithms and Libraries for Physics
Simulations) project, an open source software project to develop libraries and
application programs for the simulation of strongly correlated quantum lattice
models such as quantum magnets, lattice bosons, and strongly correlated fermion
systems. The code development is centered on common XML and HDF5 data formats,
libraries to simplify and speed up code development, common evaluation and
plotting tools, and simulation programs. The programs enable non-experts to
start carrying out serial or parallel numerical simulations by providing basic
implementations of the important algorithms for quantum lattice models:
classical and quantum Monte Carlo (QMC) using non-local updates, extended
ensemble simulations, exact and full diagonalization (ED), the density matrix
renormalization group (DMRG) both in a static version and a dynamic
time-evolving block decimation (TEBD) code, and quantum Monte Carlo solvers for
dynamical mean field theory (DMFT). The ALPS libraries provide a powerful
framework for programers to develop their own applications, which, for
instance, greatly simplify the steps of porting a serial code onto a parallel,
distributed memory machine. Major changes in release 2.0 include the use of
HDF5 for binary data, evaluation tools in Python, support for the Windows
operating system, the use of CMake as build system and binary installation
packages for Mac OS X and Windows, and integration with the VisTrails workflow
provenance tool. The software is available from our web server at
http://alps.comp-phys.org/.Comment: 18 pages + 4 appendices, 7 figures, 12 code examples, 2 table
Supersolid state of ultracold fermions in an optical lattice
We study ultracold fermionic atoms trapped in an optical lattice with
harmonic confinement by means of the dynamical mean-field approximation. It is
demonstrated that a supersolid state, where an s-wave superfluid coexists with
a density-wave state with a checkerboard pattern, is stabilized by attractive
onsite interactions on a square lattice. Our new finding here is that a
confining potential plays an invaluable role in stabilizing the supersolid
state. We establish a rich phase diagram at low temperatures, which clearly
shows how the insulator, the density wave and the superfluid compete with each
other to produce an intriguing domain structure. Our results shed light on the
possibility of the supersolid state in fermionic optical lattice systems.Comment: 5 pages, 4 figure