783 research outputs found
Atomic dynamics in evaporative cooling of trapped alkali atoms in strong magnetic fields
We investigate how the nonlinearity of the Zeeman shift for strong magnetic
fields affects the dynamics of rf field induced evaporative cooling in magnetic
traps. We demonstrate for the 87-Rb and 23-Na F=2 trapping states with wave
packet simulations how the cooling stops when the rf field frequency goes below
a certain limit (for the 85-Rb F=2 trapping state the problem does not appear).
We examine the applicability of semiclassical models for the strong field case
as an extension of our previous work [Phys. Rev. A 58, 3983 (1998)]. Our
results verify many of the aspects observed in a recent Rb experiment
[Phys. Rev. A 60, R1759 (1999)].Comment: 9 pages, RevTex, eps figures embedde
Superconducting, Insulating, and Anomalous Metallic Regimes in a Gated Two-Dimensional Semiconductor-Superconductor Array
The superconductor-insulator transition in two dimensions has been widely
investigated as a paradigmatic quantum phase transition. The topic remains
controversial, however, because many experiments exhibit a metallic regime with
saturating low-temperature resistance, at odds with conventional theory. Here,
we explore this transition in a novel, highly controllable system, a
semiconductor heterostructure with epitaxial Al, patterned to form a regular
array of superconducting islands connected by a gateable quantum well. Spanning
nine orders of magnitude in resistance, the system exhibits regimes of
superconducting, metallic, and insulating behavior, along with signatures of
flux commensurability and vortex penetration. An in-plane magnetic field
eliminates the metallic regime, restoring the direct superconductor-insulator
transition, and improves scaling, while strongly altering the scaling exponent
The short-term effect of dark chocolate flavanols on cognition in older adults: A randomized controlled trial (FlaSeCo)
Background Cocoa flavanols in the diet have had positive effects on cognition, blood lipid levels, and glucose metabolism. Methods Cognitively healthy older adults aged 65–75 years were recruited for an eight-week randomized, double-blind controlled trial to investigate the effectiveness of cocoa flavanols on cognitive functions. At baseline, nutrient and polyphenol intakes from diet were assessed with three-day food diaries. The intervention group received 50 g dark chocolate containing 410 mg of flavanols per day, and the control group 50 g dark chocolate containing 86 mg of flavanols per day, for eight weeks. Cognition was assessed with Verbal Fluency (VF) and the Trail Making Test (TMT) A and B as the main outcome measures. Changes in blood lipids and glucose were also measured. Results The older adults participating numbered 100 (63% women), mean 69 y (range 65 to 74). They were highly educated with a mean 14.9 years of education (SD 3.6). No differences in changes in cognition were seen between groups. The mean change (± SEs) in the time to complete the TMT A and B in the intervention group was −4.6 s (−7.1 to −2.1) and −16.1 s (−29.1 to −3.1), and in the controls −4.4 s (−7.0 to −1.9) and −12.5 s (−22.8 to −2.1)(TMT A p = 0.93; TMT B p = 0.66). No difference was apparent in the changes in blood lipids, glucose levels, or body weight between the groups. Conclusions The healthy older adults showed no effect from the eight-week intake of dark chocolate flavanols on cognition.Peer reviewe
Organisation of cross-sector collaboration and its influence on crisis management effectiveness among pharmaceutical supply chain stakeholders during the COVID-19 pandemic
Objectives: To investigate the organisation of cross-sector collaboration and how it influenced crisis management effectiveness among pharmaceutical supply chain stakeholders in Finland during the COVID-19 pandemic. Study design: Qualitative semi-structured interview study. Methods: Purposeful selection was used to obtain the study sample consisting of leaders and specialists from the pharmaceutical industry and wholesalers (n = 9), community pharmacy owners (n = 9), hospital pharmacy heads (n = 6), government agency directors and officials (n = 5) and advocacy organisation representatives (n = 2). Inductive content analysis was performed to examine the data from the semi-structured individual (n = 29) and paired (n = 2) interviews in March–May 2021. Results: A new conceptual model was developed to describe the organisation of collaborative crisis management. Without a predefined crisis management organisation, cross-sector collaboration was organised based on previous collaboration structures, channels and relationships and through the establishment of issue-specific groups by government agencies as per legal mandates. Crisis dynamics and related issues guided the group formation and meeting frequency. Advocacy organisations and government agencies acted in bridging role between stakeholders. Shared knowledge among pharmaceutical supply chain stakeholders enabled anticipation and preparedness during crisis; shared resources fostered maintenance of core functions; and shared problem-solving facilitated cross-sectoral solutions. Conclusion: This was the first study exploring cross-sector collaboration among pharmaceutical supply chain stakeholders during a crisis. Sharing knowledge, resources and problem-solving increased the crisis management effectiveness. The study presented a new illustration of organising for collaborative crisis management and added knowledge about private-third sector collaboration and issue-specific groups to the cross-sector collaboration and crisis management literature
Quantum and Semiclassical Calculations of Cold Atom Collisions in Light Fields
We derive and apply an optical Bloch equation (OBE) model for describing
collisions of ground and excited laser cooled alkali atoms in the presence of
near-resonant light. Typically these collisions lead to loss of atoms from
traps. We compare the results obtained with a quantum mechanical complex
potential treatment, semiclassical Landau-Zener models with decay, and a
quantum time-dependent Monte-Carlo wave packet (MCWP) calculation. We formulate
the OBE method in both adiabatic and diabatic representations. We calculate the
laser intensity dependence of collision probabilities and find that the
adiabatic OBE results agree quantitatively with those of the MCWP calculation,
and qualitatively with the semiclassical Landau-Zener model with delayed decay,
but that the complex potential method or the traditional Landau-Zener model
fail in the saturation limit.Comment: 21 pages, RevTex, 7 eps figures embedded using psfig, see also
http://www.physics.helsinki.fi/~kasuomin
Population trapping due to cavity losses
In population trapping the occupation of a decaying quantum level keeps a
constant non-zero value. We show that an atom-cavity system interacting with an
environment characterized by a non-flat spectrum, in the non-Markovian limit,
exhibits such a behavior, effectively realizing the preservation of
nonclassical states against dissipation. Our results allow to understand the
role of cavity losses in hybrid solid state systems and pave the way to the
proper description of leakage in the recently developed cavity quantum
electrodynamic systems.Comment: 4 pages, 3 figures, version accepted for publication on Phys. Rev.
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
Collisions of cold magnesium atoms in a weak laser field
We use quantum scattering methods to calculate the light-induced collisional
loss of laser-cooled and trapped magnesium atoms for detunings up to 30 atomic
linewidths to the red of the 1S_0-1P_1 cooling transition. Magnesium has no
hyperfine structure to complicate the theoretical studies. We evaluate both the
radiative and nonradiative mechanisms of trap loss. The radiative escape
mechanism via allowed 1Sigma_u excitation is dominant for more than about one
atomic linewidth detuning. Molecular vibrational structure due to
photoassociative transitions to bound states begins to appear beyond about ten
linewidths detuning.Comment: 4 pages with 3 embedded figure
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
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