6 research outputs found
Cloning of spin-coherent states
We consider optimal cloning of the spin coherent states in Hilbert spaces of
different dimensionality d. We give explicit form of optimal cloning
transformation for spin coherent states in the three-dimensional space,
analytical results for the fidelity of the optimal cloning in d=3 and d=4 as
well as numerical results for higher dimensions. In the low-dimensional case we
construct the corresponding completely positive maps and exhibit their
structure with the help of Jamiolkowski isomorphism. This allows us to
formulate some conjectures about the form of optimal coherent cloning CP maps
in arbitrary dimension.Comment: LateX, 9 pages, 1 figur
Decay rate and renormalized frequency shift of a quantum wire Wannier exciton in a planar microcavity
The superradiant decay rate and frequency shift of a Wannier exciton in a
one-dimensional quantum wire are studied. It is shown that the dark mode
exciton can be examined experimentally when the quantum wire is embedded in a
planar microcavity. It is also found that the decay rate is greatly enhanced as
the cavity length is equal to the multiple wavelength of the emitted
photon. Similar to its decay rate counterpart, the frequency shift also shows
discontinuities at resonant modes.Comment: 12 pages, 2 figures. To appear in P. R. B. September 200
Atomic motion in magneto-optical double-well potentials: A new testing ground for quantum chaos
We have identified ultra-cold atoms in magneto-optical double-well potentials
as a very clean setting in which to study the quantum and classical dynamics of
a nonlinear system with multiple degrees of freedom. In this system,
entanglement at the quantum level and chaos at the classical level arise from
nonseparable couplings between the atomic spin and its center of mass motion.
The main features of the chaotic dynamics are analyzed using action-angle
variables and Poincare surfaces of section. We show that for the initial state
prepared in current experiments [D. J. Haycock et al., Phys. Rev. Lett. 85,
3365 (2000)], the classical and quantum dynamics diverge, and the observed
experimental dynamics are best described by quantum mechanics. Furthermore, the
motion corresponds to tunneling through a dynamical potential barrier. The
coupling between the spin and the motional subsystems, which are very different
in nature from one another, leads to new questions regarding the transition
from regular quantum dynamics to chaotic classical motion.Comment: 36 pages including 6 pages of figures. To be published in PRE Nov.
1st, 2001. Revised version contains a discussion and extra figure (Fig 5)
related to gauge potentials, plus added refernce