11,118 research outputs found
Energy as an Entanglement Witness for Quantum Many-Body Systems
We investigate quantum many-body systems where all low-energy states are
entangled. As a tool for quantifying such systems, we introduce the concept of
the entanglement gap, which is the difference in energy between the
ground-state energy and the minimum energy that a separable (unentangled) state
may attain. If the energy of the system lies within the entanglement gap, the
state of the system is guaranteed to be entangled. We find Hamiltonians that
have the largest possible entanglement gap; for a system consisting of two
interacting spin-1/2 subsystems, the Heisenberg antiferromagnet is one such
example. We also introduce a related concept, the entanglement-gap temperature:
the temperature below which the thermal state is certainly entangled, as
witnessed by its energy. We give an example of a bipartite Hamiltonian with an
arbitrarily high entanglement-gap temperature for fixed total energy range. For
bipartite spin lattices we prove a theorem demonstrating that the entanglement
gap necessarily decreases as the coordination number is increased. We
investigate frustrated lattices and quantum phase transitions as physical
phenomena that affect the entanglement gap.Comment: 16 pages, 3 figures, published versio
Cold atoms in real-space optical lattices
Cold atoms in optical lattices are described in {\it real space} by
multi-orbital mean-field Ans\"atze. In this work we consider four typical
systems: (i) spinless identical bosons, (ii) spinor identical bosons (iii),
Bose-Bose mixtures, and (iv) Bose-Fermi mixtures and derive in each case the
corresponding multi-orbital mean-field energy-functional and working equations.
The notions of {\it dressed} Wannier functions and Wannier spinors are
introduced and the equations defining them are presented and discussed. The
dressed Wannier functions are the set of orthogonal, translationally-equivalent
orbitals which minimizes the energy of the Hamiltonian including boson-boson
(particle-particle) interactions. Illustrative examples of dressed Wannier
functions are provided for spinless bosonic atoms and mixtures in
one-dimensional optical lattices.Comment: 27 pages, 4 figures; [version minus figures published
Thermodynamics of (2+1)-flavor QCD
We report on the status of our QCD thermodynamics project. It is performed on
the QCDOC machine at Brookhaven National Laboratory and the APEnext machine at
Bielefeld University. Using a 2+1 flavor formulation of QCD at almost realistic
quark masses we calculated several thermodynamical quantities. In this
proceeding we show the susceptibilites of the chiral condensate and the
Polyakov loop, the static quark potential and the spatial string tension.Comment: To appear in the proceedings of International Conference on Strong
and Electroweak Matter (SEWM 2006), Upton, New York, 10-13 May 200
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