4,988 research outputs found
Entanglement generation via a completely mixed nuclear spin bath
We show that qubits coupled sequentially to a mesoscopic static completely
mixed spin bath via the Heisenberg interaction can become highly entangled.
Straightforward protocols for the generation of multipartite entangled
(Greenberger-Horne-Zeilinger-)states are presented. We show the feasibility of
an experimental realization in a quantum dot by the hyperfine interaction of an
electron with the nuclear spins.Comment: 4+pages, 3 figure
Infrared analysis of propagators and vertices of Yang--Mills theory in Landau and Coulomb gauge
The infrared behaviour of gluon and ghost propagators, ghost-gluon vertex and
three-gluon vertex is investigated for both the covariant Landau and the
non-covariant Coulomb gauge. Assuming infrared ghost dominance, we find a
unique infrared exponent in the d=4 Landau gauge, while in the d=3+1 Coulomb
gauge we find two different infrared exponents. We also show that a finite
dressing of the ghost-gluon vertex has no influence on the infrared exponents.
Finally, we determine the infrared behaviour of the three-gluon vertex
analytically and calculate it numerically at the symmetric point in the Coulomb
gauge.Comment: 25 pages, 6 figures, accepted by Phys. Rev. D, references added,
typos correcte
Relativistic Heavy Quark Effective Action
We study the fermion action needed to accurately describe the low energy
physics of systems including heavy quarks in lattice QCD even when the heavy
fermion mass is on the order of, or larger than, the inverse lattice
spacing: . We carry out an expansion through first order in (where is the heavy quark momentum) and all orders in ,
refining the analysis of the Fermilab and Tsukuba groups. We demonstrate that
the spectrum of heavy quark bound states can be determined accurately through
and for arbitrary exponent by using a lattice action
containing only three unknown coefficients: , and (a
generalization of ), which are functions of . In a companion paper,
we show how these three coefficients can be precisely determined using
non-perturbative techniques.Comment: 40 pages, 1 figur
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