81,732 research outputs found
Reversibility Checking for Markov Chains
In this paper, we present reversibility preserving operations on Markov chain
transition matrices. Simple row and column operations allow us to create new
reversible transition matrices and yield an easy method for checking a Markov
chain for reversibility
Accurate determination of tensor network state of quantum lattice models in two dimensions
We have proposed a novel numerical method to calculate accurately the
physical quantities of the ground state with the tensor-network wave function
in two dimensions. We determine the tensor network wavefunction by a projection
approach which applies iteratively the Trotter-Suzuki decomposition of the
projection operator and the singular value decomposition of matrix. The norm of
the wavefunction and the expectation value of a physical observable are
evaluated by a coarse grain renormalization group approach. Our method allows a
tensor-network wavefunction with a high bond degree of freedom (such as D=8) to
be handled accurately and efficiently in the thermodynamic limit. For the
Heisenberg model on a honeycomb lattice, our results for the ground state
energy and the staggered magnetization agree well with those obtained by the
quantum Monte Carlo and other approaches.Comment: 4 pages 5 figures 2 table
NMR Probing Spin Excitations in the Ring-Like Structure of a Two-Subband System
Resistively detected nuclear magnetic resonance (NMR) is observed inside the
ring-like structure, with a quantized Hall conductance of 6e^2/h, in the phase
diagram of a two subband electron system. The NMR signal persists up to 400 mK
and is absent in other states with the same quantized Hall conductance. The
nuclear spin-lattice relaxation time, T1, is found to decrease rapidly towards
the ring center. These observations are consistent with the assertion of the
ring-like region being a ferromagnetic state that is accompanied by collective
spin excitations.Comment: 4 pages, 4 figure
Superfluid-Mott-Insulator Transition in a One-Dimensional Optical Lattice with Double-Well Potentials
We study the superfluid-Mott-insulator transition of ultracold bosonic atoms
in a one-dimensional optical lattice with a double-well confining trap using
the density-matrix renormalization group. At low density, the system behaves
similarly as two separated ones inside harmonic traps. At high density,
however, interesting features appear as the consequence of the quantum
tunneling between the two wells and the competition between the "superfluid"
and Mott regions. They are characterized by a rich step-plateau structure in
the visibility and the satellite peaks in the momentum distribution function as
a function of the on-site repulsion. These novel properties shed light on the
understanding of the phase coherence between two coupled condensates and the
off-diagonal correlations between the two wells.Comment: 5 pages, 7 figure
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Nonlinear stability of <i>E</i> centers in Si<sub>1-<i>x</i></sub>Ge<sub><i>x</i></sub>: electronic structure calculations
Electronic structure calculations are used to investigate the binding energies of defect pairs composed of lattice vacancies and phosphorus or arsenic atoms (E centers) in silicon-germanium alloys. To describe the local environment surrounding the E center we have generated special quasirandom structures that represent random silicon-germanium alloys. It is predicted that the stability of E centers does not vary linearly with the composition of the silicon-germanium alloy. Interestingly, we predict that the nonlinear behavior does not depend on the donor atom of the E center but only on the host lattice. The impact on diffusion properties is discussed in view of recent experimental and theoretical results
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