3,901 research outputs found
Entangling spins by measuring charge: a parity-gate toolbox
The parity gate emerged recently as a promising resource for performing
universal quantum computation with fermions using only linear interactions.
Here we analyse the parity gate (P-gate) from a theoretical point of view in
the context of quantum networks. We present several schemes for entanglement
generation with P-gates and show that native networks simplify considerably the
resources required for producing multi-qubit entanglement, like n-GHZ states.
Other applications include a Bell-state analyser and teleportation. We also
show that cluster state fusion can be performed deterministically with parity
measurements. We then extend this analysis to hybrid quantum networks
containing spin and mode qubits. Starting from an easy-to-prepare resource
(spin-mode entanglement of single electrons) we show how to produce a spin
n-GHZ state with linear elements (beam-splitters and local spin-flips) and
charge-parity detectors; this state can be used as a resource in a spin quantum
computer or as a precursor for constructing cluster states. Finally, we
construct a novel spin CZ-gate by using the mode degrees of freedom as
ancillae.Comment: updated to the published versio
Neutron methods for the direct determination of the magnetic induction in thick films
We review different neutron methods which allow extracting directly the value
of the magnetic induction in thick films: Larmor precession, Zeeman spatial
beam-splitting and neutron spin resonance. Resulting parameters obtained by the
neutron methods and standard magnetometry technique are presented and compared.
The possibilities and specificities of the neutron methods are discussed
On Yang-Mills instantons in a spherically symmetric background
We present arguments for the existence of self-dual Yang-Mills instantons for
several spherically symmetric backgrounds with Euclidean signature. The
time-independent Yang-Mills field has finite action and a vanishing energy
momentum tensor and does not disturb the geometry. We conjecture the existence
of similar solutions for any nonextremal SO(3)-spherically symmetric
background.Comment: 6 pages, 3 figures; v2: references adde
Einstein-Yang-Mills-Chern-Simons solutions in D=2n+1 dimensions
We investigate finite energy solutions of the
Einstein--Yang-Mills--Chern-Simons system in odd spacetime dimensions, D=2n+1,
with n>1. Our configurations are static and spherically symmetric, approaching
at infinity a Minkowski spacetime background. In contrast with the Abelian
case, the contribution of the Chern-Simons term is nontrivial already in the
static, spherically symmetric limit. Both globally regular, particle-like
solutions and black holes are constructed numerically for several values of D.
These solutions carry a nonzero electric charge and have finite mass. For
globally regular solutions, the value of the electric charge is fixed by the
Chern-Simons coupling constant. The black holes can be thought as non-linear
superpositions of Reissner-Nordstrom and non-Abelian configurations. A
systematic discussion of the solutions is given for D=5, in which case the
Reissner-Nordstrom black hole becomes unstable and develops non-Abelian hair.
We show that some of these non-Abelian configurations are stable under linear,
spherically symmetric perturbations. A detailed discussion of an exact D=5
solution describing extremal black holes and solitons is also provided.Comment: 34 pages, 14 figures; v2: misprints corrected and references adde
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