38 research outputs found
Comment on "Impossibility of distant indirect measurement of the quantum Zeno effect"
In the paper by M. Hotta and M. Morikawa [Phys. Rev. A 69, 052114 (2004)] the
non-existence of the quantum Zeno effect caused by indirect measurements has
been claimed. It is shown here that the pertinent proof is incorrect, and the
claim unfounded.Comment: 2 pages, to be published in Phys. Rev. A, comment on quant-ph/031009
Coarse grained and fine dynamics in trapped ion Raman schemes
A novel result concerning Raman coupling schemes in the context of trapped
ions is obtained. By means of an operator perturbative approach, it is shown
that the complete time evolution of these systems (in the interaction picture)
can be expressed, with a high degree of accuracy, as the product of two unitary
evolutions. The first one describes the time evolution related to an effective
coarse grained dynamics. The second is a suitable correction restoring the {\em
fine} dynamics suppressed by the coarse graining performed to adiabatically
eliminate the nonresonantly coupled atomic level.Comment: 12 pages, no figure
Influence of dissipation on the extraction of quantum states via repeated measurements
A quantum system put in interaction with another one that is repeatedly
measured is subject to a non-unitary dynamics, through which it is possible to
extract subspaces. This key idea has been exploited to propose schemes aimed at
the generation of pure quantum states (purification). All such schemes have so
far been considered in the ideal situations of isolated systems. In this paper,
we analyze the influence of non-negligible interactions with environment during
the extraction process, with the scope of investigating the possibility of
purifying the state of a system in spite of the sources of dissipation. A
general framework is presented and a paradigmatic example consisting of two
interacting spins immersed in a bosonic bath is studied. The effectiveness of
the purification scheme is discussed in terms of purity for different values of
the relevant parameters and in connection with the bath temperature.Comment: 10 pages, 3 figure
Raman cooling and heating of two trapped Ba+ ions
We study cooling of the collective vibrational motion of two 138Ba+ ions
confined in an electrodynamic trap and irradiated with laser light close to the
resonances S_1/2-P_1/2 (493 nm) and P_1/2-D_3/2 (650 nm). The motional state of
the ions is monitored by a spatially resolving photo multiplier. Depending on
detuning and intensity of the cooling lasers, macroscopically different
motional states corresponding to different ion temperatures are observed. We
also derive the ions' temperature from detailed analytical calculations of
laser cooling taking into account the Zeeman structure of the energy levels
involved. The observed motional states perfectly match the calculated
temperatures. Significant heating is observed in the vicinity of the dark
resonances of the Zeeman-split S_1/2-D_3/2 Raman transitions. Here two-photon
processes dominate the interaction between lasers and ions. Parameter regimes
of laser light are identified that imply most efficient laser cooling.Comment: 8 pages, 5 figure