317 research outputs found
"Super-radiance" and the width of exotic baryons
It is suggested that the narrow width of the recently observed resonance
with strangeness could be a result of the
super-radiance mechanism of the redistribution of the widths of overlapping
resonances due to their coupling through common decay channels.Comment: This is an update of the original version submitted on October 08,
2003; it includes consideration of an additional model and one new figur
Neutron Resonance Widths and the Porter-Thomas Distribution
Experimental evidence has recently put the validity of the Porter-Thomas
distribution (PTD) for partial neutron widths into question. We identify two
terms in the effective Hamiltonian that violate orthogonal invariance (the
basis for the PTD). Both are due to the coupling to the decay channels. We show
that realistic estimates for the coupling to the neutron channel and for
non-statistical gamma decays yield significant modifications of the PTD.Comment: 5 pages, 2 figure
Quantum signal transmission through a single-qubit chain
A system of a two-level atom of an impurity (qubit) inserted into a periodic
chain coupled to the continuum is studied with the use of the effective
non-Hermitian Hamiltonian. Exact solutions are derived for the quasistationary
eigenstates, their complex energies, and transport properties. Due to the
presence of the qubit, two long-lived states corresponding to the ground and
excited states of the qubit emerge outside the Bloch energy band. These states
remain essentially localized at the qubit even in the limit of sufficiently
strong coupling between the chain and the environment when the super-radiant
states are formed. The transmission through the chain is studied as a function
of the continuum coupling strength and the chain-qubit coupling; the perfect
resonance transmission takes place through isolated resonances at weak and
strong continuum coupling, while the transmission is lowered in the
intermediate regime.Comment: In this version we added the case of large N and the case when the
excitation energy of bare qubit is below the band boundary of the bare chain.
The captions to some figures are modified. Some new references are adde
- …