7 research outputs found
Comment on "Loss-error compensation in quantum-state measurements"
In the two papers [T. Kiss, U. Herzog, and U. Leonhardt, Phys. Rev. A 52,
2433 (1995); U. Herzog, Phys. Rev. A 53, 1245 (1996)] with titles similar to
the one given above, the authors assert that in some cases it is possible to
compensate a quantum efficiency in quantum-state measurements,
violating the lower bound 1/2 proved in a preceding paper [G. M. D'Ariano, U.
Leonhardt and H. Paul, Phys. Rev. A 52, R1801 (1995)]. Here we re-establish the
bound as unsurpassable for homodyning any quantum state, and show how the
proposed loss-compensation method would always fail in a real measurement
outside the allowed region.Comment: 3 pages, RevTeX, 2 figures included, to appear on Phys. Rev. A (April
1998
Nonlinear Decoherence in Quantum State Preparation of a Trapped Ion
We present a nonlinear decoherence model which models decoherence effect
caused by various decohereing sources in a quantum system through a nonlinear
coupling between the system and its environment, and apply it to investigating
decoherence in nonclassical motional states of a single trapped ion. We obtain
an exactly analytic solution of the model and find very good agreement with
experimental results for the population decay rate of a single trapped ion
observed in the NIST experiments by Meekhof and coworkers (D. M. Meekhof, {\it
et al.}, Phys. Rev. Lett. {\bf 76}, 1796 (1996)).Comment: 5 pages, Revte
Self-homodyne tomography of a twin-beam state
A self-homodyne detection scheme is proposed to perform two-mode tomography
on a twin-beam state at the output of a nondegenerate optical parametric
amplifier. This scheme has been devised to improve the matching between the
local oscillator and the signal modes, which is the main limitation to the
overall quantum efficiency in conventional homodyning. The feasibility of the
measurement is analyzed on the basis of Monte-Carlo simulations, studying the
effect of non-unit quantum efficiency on detection of the correlation and the
total photon-number oscillations of the twin-beam state.Comment: 13 pages (two-column ReVTeX) including 21 postscript figures; to
appear on Phys. Rev.