1,235 research outputs found
Grover's algorithm on a Feynman computer
We present an implementation of Grover's algorithm in the framework of
Feynman's cursor model of a quantum computer. The cursor degrees of freedom act
as a quantum clocking mechanism, and allow Grover's algorithm to be performed
using a single, time-independent Hamiltonian. We examine issues of locality and
resource usage in implementing such a Hamiltonian. In the familiar language of
Heisenberg spin-spin coupling, the clocking mechanism appears as an excitation
of a basically linear chain of spins, with occasional controlled jumps that
allow for motion on a planar graph: in this sense our model implements the idea
of "timing" a quantum algorithm using a continuous-time random walk. In this
context we examine some consequences of the entanglement between the states of
the input/output register and the states of the quantum clock
Magnetooptical sum rules close to the Mott transition
We derive new sum rules for the real and imaginary parts of the
frequency-dependent Hall constant and Hall conductivity. As an example, we
discuss their relevance to the doped Mott insulator that we describe within the
dynamical mean-field theory of strongly correlated electron systems.Comment: 4 pages, 4 ps figures; accepted for publication in PR
Measuring topology in a laser-coupled honeycomb lattice: From Chern insulators to topological semi-metals
Ultracold fermions trapped in a honeycomb optical lattice constitute a
versatile setup to experimentally realize the Haldane model [Phys. Rev. Lett.
61, 2015 (1988)]. In this system, a non-uniform synthetic magnetic flux can be
engineered through laser-induced methods, explicitly breaking time-reversal
symmetry. This potentially opens a bulk gap in the energy spectrum, which is
associated with a non-trivial topological order, i.e., a non-zero Chern number.
In this work, we consider the possibility of producing and identifying such a
robust Chern insulator in the laser-coupled honeycomb lattice. We explore a
large parameter space spanned by experimentally controllable parameters and
obtain a variety of phase diagrams, clearly identifying the accessible
topologically non-trivial regimes. We discuss the signatures of Chern
insulators in cold-atom systems, considering available detection methods. We
also highlight the existence of topological semi-metals in this system, which
are gapless phases characterized by non-zero winding numbers, not present in
Haldane's original model.Comment: 30 pages, 12 figures, 4 Appendice
Dynamical Properties in the Bilayer Quantum Hall Ferromagnet
The spectral functions of the pseudospin correlation functions in the bilayer
quantum Hall system at \nu=1 are investigated numerically, where the pseudospin
describes the layer degrees of freedom. In the pseudospin-ferromagnetic phase,
the lowest-energy excitation branch is closely connected with the ground state
through the fluctuations of pseudospin S_y and S_z, and it plays a significant
role on the tunneling properties in this system. For the system with very small
tunneling amplitude and layer separation smaller than the critical one, the
system-size dependence of calculated spectral function A_{y z} suggests the
superfluidity on the tunneling current in the absence of impurities.Comment: 4 pages, 1 Postscript figur
Pseudo-spin canting transition in bilayer quantum Hall ferromagnets: a self-charging capacitor
For sufficiently strong in-plane magnetic field a bilayer quantum
Hall pseudo-ferromagnet is expected to exhibit a soliton lattice. For
sufficiently close layers and large in-plane field, we predict this
incommensurate ``planar'' phase to undergo a reentrant pseudo-spin
canting transition to an incommensurate state , with a finite out-of-plane
pseudo-magnetization component, corresponding to an interlayer charge imbalance
in regions between solitons. At the transition is in the 2d compressible
Ising universality class, and at T=0, the quantum transition is in heretofore
unexplored universality class. The striking experimental signatures are the
universal nonlinear charge-voltage and in-plane field relations, and the
divergence of the differential bilayer capacitance at the transition, resulting
in a bilayer capacitor that spontaneously charges itself, even in the absence
of an applied interlayer voltage.Comment: 4 RevTeX pgs, 1 eps figures, submitted to PR
Genetic heterogeneity and trans regulators of gene expression
Heterogeneity poses a challenge to linkage mapping. Here, we apply a latent class extension of Haseman-Elston regression to expression phenotypes with significant evidence of linkage to trans regulators in 14 large pedigrees. We test for linkage, accounting for heterogeneity, and classify individual families as "linked" and "unlinked" on the basis of their contribution to the overall evidence of linkage
Strong Correlation to Weak Correlation Phase Transition in Bilayer Quantum Hall Systems
At small layer separations, the ground state of a nu=1 bilayer quantum Hall
system exhibits spontaneous interlayer phase coherence and has a
charged-excitation gap E_g. The evolution of this state with increasing layer
separation d has been a matter of controversy. In this letter we report on
small system exact diagonalization calculations which suggest that a single
phase transition, likely of first order, separates coherent incompressible (E_g
>0) states with strong interlayer correlations from incoherent compressible
states with weak interlayer correlations. We find a dependence of the phase
boundary on d and interlayer tunneling amplitude that is in very good agreement
with recent experiments.Comment: 4 pages, 4 figures included, version to appear in Phys. Rev. Let
Stability of the Excitonic Phase in Bilayer Quantum Hall Systems at Total Filling One -- Effects of Finite Well Width and Pseudopotentials --
The ground state of a bilayer quantum Hall system at with
model pseudopotential is investigated by the DMRG method. Firstly,
pseudopotential parameters appropriate for the system with finite layer
thickness are derived, and it is found that the finite thickness makes the
excitonic phase more stable. Secondly, a model, where only a few
pseudopotentials with small relative angular momentum have finite values, is
studied, and it is clarified how the excitonic phase is destroyed as
intra-layer pseudopotential becomes larger. The importance of the intra-layer
repulsive interaction at distance twice of the magnetic length for the
destruction of the excitonic phase is found.Comment: 7 pages, 7 figure
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