453 research outputs found
Weisskopf-Wigner model for wave packet excitation
We consider a laser induced molecular excitation process as a decay of a
single energy state into a continuum. The analytic results based on
Weisskopf-Wigner approach and perturbation calculations are compared with
numerical wave packet results. We find that the decay model describes the
excitation process well within the expected parameter region.Comment: 14 pages, Latex2.09, 9 Postscript figures embedded using psfig, see
also http://www.physics.helsinki.fi/~kasuomin
Detection of atomic entanglement and electromagnetically induced transparency in velocity-selective coherent population trapping
We investigate theoretically the optical properties of an atomic gas which
has been cooled by the laser cooling method velocity-selective coherent
population trapping. We demonstrate that the application of a weak laser pulse
gives rise to a backscattered pulse, which is a direct signal for the
entanglement in the atomic system, and which leads to single-particle
entanglement on the few-photon level. If the pulse is applied together with the
pump lasers, it also displays the phenomenon of electromagnetically induced
transparency. We suggest that the effect should be observable in a gas of
Rubidium atoms.Comment: Revtex, 9 pages, 6 figures. To appear in Physical Review
Open system dynamics with non-Markovian quantum jumps
We discuss in detail how non-Markovian open system dynamics can be described
in terms of quantum jumps [J. Piilo et al., Phys. Rev. Lett. 100, 180402
(2008)]. Our results demonstrate that it is possible to have a jump description
contained in the physical Hilbert space of the reduced system. The developed
non-Markovian quantum jump (NMQJ) approach is a generalization of the Markovian
Monte Carlo Wave Function (MCWF) method into the non-Markovian regime. The
method conserves both the probabilities in the density matrix and the norms of
the state vectors exactly, and sheds new light on non-Markovian dynamics. The
dynamics of the pure state ensemble illustrates how local-in-time master
equation can describe memory effects and how the current state of the system
carries information on its earlier state. Our approach solves the problem of
negative jump probabilities of the Markovian MCWF method in the non-Markovian
regime by defining the corresponding jump process with positive probability.
The results demonstrate that in the theoretical description of non-Markovian
open systems, there occurs quantum jumps which recreate seemingly lost
superpositions due to the memory.Comment: 19 pages, 10 figures. V2: Published version. Discussion section
shortened and some other minor changes according to the referee's suggestion
Sudden death and sudden birth of entanglement in common structured reservoirs
We study the exact entanglement dynamics of two qubits in a common structured
reservoir. We demonstrate that, for certain classes of entangled states,
entanglement sudden death occurs, while for certain initially factorized
states, entanglement sudden birth takes place. The backaction of the
non-Markovian reservoir is responsible for revivals of entanglement after
sudden death has occurred, and also for periods of disentanglement following
entanglement sudden birth.Comment: 4 pages, 2 figure
Measuring the Density Matrix by Local Addressing
We introduce a procedure to measure the density matrix of a material system.
The density matrix is addressed locally in this scheme by applying a sequence
of delayed light pulses. The procedure is based on the stimulated Raman
adiabatic passage (STIRAP) technique. It is shown that a series of population
measurements on the target state of the population transfer process yields
unambiguous information about the populations and coherences of the addressed
states, which therefore can be determined.Comment: 4 pages, 1 figur
Fidelity balance in quantum operations
I derive a tight bound between the quality of estimating the state of a
single copy of a -level system, and the degree the initial state has to be
altered in course of this procedure. This result provides a complete analytical
description of the quantum mechanical trade-off between the information gain
and the quantum state disturbance expressed in terms of mean fidelities. I also
discuss consequences of this bound for quantum teleportation using nonmaximally
entangled states.Comment: 4 pages, REVTeX. Revised versio
Trajectories of work ability from mid-life to pensionable age and their association with retirement timing
BACKGROUND: This study aimed to identify the trajectories of work ability over 16 years preceding the individual pensionable age and to examine the association with retirement timing. METHODS: The study population consisted of 2612 public sector employees from the Finnish Retirement and Aging study and the Finnish Public Sector study. Participants were grouped into 'no-extension' (retired at the individual pensionable date or worked no longer than 6 months after that date) and 'extension' (worked more than 6 months after individual pensionable age). Trajectories of self-reported work ability score (0-10) in maximum of eight measurement points over 16 years preceding retirement were examined using the group-based latent trajectory analysis. Log-binomial regression was used to analyse the association between trajectory groups and extended employment. RESULTS: Four stable ('Stable excellent', 7%; 'Stable high', 62%; 'Stable medium', 24%; 'Low', 4%) and one decreasing ('Declining', 3%) work ability trajectories were identified. After taking into account gender, age, occupational status, marital status and self-rated health, 'Stable excellent' trajectory was associated with a higher likelihood of extended employment compared with the 'Low' (risk ratio (RR) 2.38, 95% CI 1.21 to 4.68) and to the 'Declining' (RR 2.82, 95% CI 1.32 to 6.01) trajectories. There was no difference in retirement timing between 'Declining', 'Low' and 'Stable medium' trajectories. CONCLUSION: Work ability remained relatively stable among majority of the participants over 16 years of follow-up. Stable excellent work ability from mid-life to late career was associated with higher likelihood of extending employment beyond individual pensionable age than those with low or declining work ability
Changes in life satisfaction during the transition to retirement : findings from the FIREA cohort study
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