199 research outputs found

### An open--quantum--system formulation of particle decay

We consider an open quantum system which contains unstable states. The time
evolution of the system can be described by an effective non-hermitian
Hamiltonian H_{eff}, in accord with the Wigner--Weisskopf approximation, and an
additional term of the Lindblad form, the socalled dissipator. We show that,
after enlarging the original Hilbert space by states which represent the decay
products of the unstable states, the non-hermitian part of H_{eff} --the
``particle decay''-- can be incorporated into the dissipator of the enlarged
space via a specific Lindblad operator. Thus the new formulation of the time
evolution on the enlarged space has a hermitian Hamiltonian and is probability
conserving. The equivalence of the new formulation with the original one
demonstrates that the time evolution which is governed by a non-hermitian
Hamiltonian and a dissipator of the Lindblad form is nevertheless completely
positive, just as systems with hermitian Hamiltonians.Comment: 8 page

### Hawking Radiation via Gravitational Anomalies in Non-spherical Topologies

We study the method of calculating the Hawking radiation via gravitational
anomalies in gravitational backgrounds of constant negative curvature. We apply
the method to topological black holes and also to topological black holes
conformally coupled to a scalar field.Comment: 25 pages, no figures, version to be published in Phys. Rev.

### Canonical Formalism for a 2n-Dimensional Model with Topological Mass Generation

The four-dimensional model with topological mass generation that was found by
Dvali, Jackiw and Pi has recently been generalized to any even number of
dimensions (2n-dimensions) in a nontrivial manner in which a Stueckelberg-type
mass term is introduced [S. Deguchi and S. Hayakawa, Phys. Rev. D 77, 045003
(2008), arXiv:0711.1446]. The present paper deals with a self-contained model,
called here a modified hybrid model, proposed in this 2n-dimensional
generalization and considers the canonical formalism for this model. For the
sake of convenience, the canonical formalism itself is studied for a model
equivalent to the modified hybrid model by following the recipe for treating
constrained Hamiltonian systems. This formalism is applied to the canonical
quantization of the equivalent model in order to clarify observable and
unobservable particles in the model. The equivalent model (with a gauge-fixing
term) is converted to the modified hybrid model (with a corresponding
gauge-fixing term) in a Becchi-Rouet-Stora-Tyutin (BRST)-invariant manner.
Thereby it is shown that the Chern-Pontryagin density behaves as an observable
massive particle (or field). The topological mass generation is thus verified
at the quantum-theoretical level.Comment: 29 pages, no figures, minor corrections, published versio

### Can an odd number of fermions be created due to chiral anomaly?

We describe a possibility of creation of an odd number of fractionally
charged fermions in 1+1 dimensional Abelian Higgs model. We point out that for
1+1 dimensions this process does not violate any symmetries of the theory, nor
makes it mathematically inconsistent. We construct the proper definition of the
fermionic determinant in this model and underline its non-trivial features that
are of importance for realistic 3+1 dimensional models with fermion number
violation.Comment: 12 pages revtex, 2 figure

### Commuting multiparty quantum observables and local compatibility

A formula for the commutator of tensor product matrices is used to shows
that, for qubits, compatibility of quantum multiparty observables almost never
implies local compatibility at each site and to predict when this happens/does
not happen in a concise manner. In particular, it is shown that two ``fully
nontrivial'' $n$-qubit observables are compatible locally and globally if and
only if they are equal up to sign. In addition, the formula gives insight into
the construction of new paradoxes of the type of the Kochen-Specker Theorem,
which can then be easily rephrased into proposals for new no hidden variable
experiments of the type of the ``Bell Theorem without inequalities''.Comment: 6 page

### Decoherence modes of entangled qubits within neutron interferometry

We study two different decoherence modes for entangled qubits by considering
a Liouville - von Neumann master equation. Mode A is determined by projection
operators onto the eigenstates of the Hamiltonian and mode B by projectors onto
rotated states. We present solutions for general and for Bell diagonal states
and calculate for the later the mixedness and the amount of entanglement given
by the concurrence.
We propose a realization of the decoherence modes within neutron
interferometry by applying fluctuating magnetic fields. An experimental test of
the Kraus operator decomposition describing the evolution of the system for
each mode is presented.Comment: 15 pages, 5 figure

- â€¦