20,132 research outputs found
Efficient Schemes for Reducing Imperfect Collective Decoherences
We propose schemes that are efficient when each pair of qubits undergoes some
imperfect collective decoherence with different baths. In the proposed scheme,
each pair of qubits is first encoded in a decoherence-free subspace composed of
two qubits. Leakage out of the encoding space generated by the imperfection is
reduced by the quantum Zeno effect. Phase errors in the encoded bits generated
by the imperfection are reduced by concatenation of the decoherence-free
subspace with either a three-qubit quantum error correcting code that corrects
only phase errors or a two-qubit quantum error detecting code that detects only
phase errors, connected with the quantum Zeno effect again.Comment: no correction, 3 pages, RevTe
Base manifolds for fibrations of projective irreducible symplectic manifolds
Given a projective irreducible symplectic manifold of dimension , a
projective manifold and a surjective holomorphic map with
connected fibers of positive dimension, we prove that is biholomorphic to
the projective space of dimension . The proof is obtained by exploiting two
geometric structures at general points of : the affine structure arising
from the action variables of the Lagrangian fibration and the structure
defined by the variety of minimal rational tangents on the Fano manifold
A conserved variable in the perturbed hydrodynamic world model
We introduce a scalar-type perturbation variable which is conserved in
the large-scale limit considering general sign of three-space curvature (),
the cosmological constant (), and time varying equation of state. In a
pressureless medium is {\it exactly conserved} in all scales.Comment: 4 pages, no figure, To appear in Phys. Rev.
Unified Analysis of Cosmological Perturbations in Generalized Gravity
In a class of generalized Einstein's gravity theories we derive the equations
and general asymptotic solutions describing the evolution of the perturbed
universe in unified forms. Our gravity theory considers general couplings
between the scalar field and the scalar curvature in the Lagrangian, thus
includes broad classes of generalized gravity theories resulting from recent
attempts for the unification. We analyze both the scalar-type mode and the
gravitational wave in analogous ways. For both modes the large scale evolutions
are characterized by the same conserved quantities which are valid in the
Einstein's gravity. This unified and simple treatment is possible due to our
proper choice of the gauges, or equivalently gauge invariant combinations.Comment: 4 pages, revtex, no figure
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