4,356 research outputs found
Atom laser dynamics in a tight-waveguide
We study the transient dynamics that arise during the formation of an atom
laser beam in a tight waveguide. During the time evolution the density profile
develops a series of wiggles which are related to the diffraction in time
phenomenon. The apodization of matter waves, which relies on the use of smooth
aperture functions, allows to suppress such oscillations in a time interval,
after which there is a revival of the diffraction in time. The revival time
scale is directly related to the inverse of the harmonic trap frequency for the
atom reservoir.Comment: 6 pages, 5 figures, to be published in the Proceedings of the 395th
WE-Heraeus Seminar on "Time Dependent Phenomena in Quantum Mechanics ",
organized by T. Kramer and M. Kleber (Blaubeuren, Germany, September 2007
Stability of spinor Fermi gases in tight waveguides
The two and three-body correlation functions of the ground state of an
optically trapped ultracold spin-1/2 Fermi gas (SFG) in a tight waveguide (1D
regime) are calculated in the plane of even and odd-wave coupling constants,
assuming a 1D attractive zero-range odd-wave interaction induced by a 3D p-wave
Feshbach resonance, as well as the usual repulsive zero-range even-wave
interaction stemming from 3D s-wave scattering. The calculations are based on
the exact mapping from the SFG to a ``Lieb-Liniger-Heisenberg'' model with
delta-function repulsions depending on isotropic Heisenberg spin-spin
interactions, and indicate that the SFG should be stable against three-body
recombination in a large region of the coupling constant plane encompassing
parts of both the ferromagnetic and antiferromagnetic phases. However, the
limiting case of the fermionic Tonks-Girardeau gas (FTG), a spin-aligned 1D
Fermi gas with infinitely attractive p-wave interactions, is unstable in this
sense. Effects due to the dipolar interaction and a Zeeman term due to a
resonance-generating magnetic field do not lead to shrinkage of the region of
stability of the SFG.Comment: 5 pages, 6 figure
Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field
We use neutron diffraction to probe the magnetization components of a crystal
of Mn12 single-molecule magnets. Each of these molecules behaves, at low
temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the
crystallographic c axis. Application of a magnetic field perpendicular to c
induces quantum tunneling between opposite spin orientations, enabling the
spins to attain thermal equilibrium. Below approximately 0.9 K, intermolecular
interactions turn this equilibrium state into a ferromagnetically ordered
phase. However, long range ferromagnetic correlations nearly disappear for
fields larger 5.5 T, possibly suggesting the existence of a quantum critical
point.Comment: 4 pages, 4 figure
Exclusive light particle measurements for the system F + C at 96 MeV
Decay sequence of hot {31}^P nucleus has been investigated through
exclusive light charged particle measurements in coincidence with individual
evaporation residues using the reaction {19}^F (96 MeV) + {12}^C.
Information on the sequential decay chain have been extracted by confronting
the data with the predictions of the statistical model. It is observed from the
present analysis that such exclusive light charged particle data may be used as
a powerful tool to probe the decay sequence of the hot light compound systems.Comment: 13 pages, 8 figures, Physical Review C (in press
Shortcuts to adiabaticity in a time-dependent box
A method is proposed to drive an ultrafast non-adiabatic dynamics of an
ultracold gas trapped in a box potential. The resulting state is free from
spurious excitations associated with the breakdown of adiabaticity, and
preserves the quantum correlations of the initial state up to a scaling factor.
The process relies on the existence of an adiabatic invariant and the inversion
of the dynamical self-similar scaling law dictated by it. Its physical
implementation generally requires the use of an auxiliary expulsive potential
analogous to those used in soliton control. The method is extended to a broad
family of many-body systems. As illustrative examples we consider the ultrafast
expansion of a Tonks-Girardeau gas and of Bose-Einstein condensates in
different dimensions, where the method exhibits an excellent robustness against
different regimes of interactions and the features of an experimentally
realizable box potential.Comment: 6 pp, 4 figures, typo in Eq. (6) fixe
Exact propagators for atom-laser interactions
A class of exact propagators describing the interaction of an -level atom
with a set of on-resonance -lasers is obtained by means of the Laplace
transform method. State-selective mirrors are described in the limit of strong
lasers. The ladder, V and configurations for a three-level atom are
discussed. For the two level case, the transient effects arising as result of
the interaction between both a semi-infinite beam and a wavepacket with the
on-resonance laser are examined.Comment: 13 pages, 6 figure
SilvAdapt.Net: A Site-Based Network of Adaptive Forest Management Related to Climate Change in Spain
Adaptive forest management (AFM) is an urgent need because of the uncertainty regarding how changes in the climate will affect the structure, composition and function of forests during the next decades. Current research initiatives for the long-term monitoring of impacts of silviculture are scattered and not integrated into research networks, with the consequent losses of opportunities and capacity for action. To increase the scientific and practical impacts of these experiences, it is necessary to establish logical frameworks that harmonize the information and help us to define the most appropriate treatments. In this context, a number of research groups in Spain have produced research achievements and know-how during the last decades that can allow for the improvement in AFM. These groups address the issue of AFM from different fields, such as ecophysiology, ecohydrology and forest ecology, thus resulting in valuable but dispersed expertise. The main objective of this work is to introduce a comprehensive strategy aimed to study the implementation of AFM in Spain. As a first step, a network of 34 experimental sites managed by 14 different research groups is proposed and justified. As a second step, the most important AFM impacts on Mediterranean pines, as one of the most extended natural and planted forest types in Spain, are presented. Finally, open questions dealing with key aspects when attempting to implement an AFM framework are discussed. This study is expected to contribute to better outlining the procedures and steps needed to implement regional frameworks for AFMA.J. Molina is beneficiary of an “APOSTD” fellowship (APOSTD/2019/111) funded
by the Generalitat Valenciana. M. Moreno-de las Heras is beneficiary of a Serra Hunter fellowship (UB-LE-9055) funded by the Generalitat de Catalunya. F.J. Ruiz-Gómez is supported by a
postdoctoral fellowship of the Junta de Andalucía (Sevilla, Spain), and the European Social Fund
2014–2020 Program (DOC_0055). The authors received national and international funding through
the following projects: SILVADAPT.NET (RED2018-102719-T), ESPECTRAMED (CGL2017-86161-R),
Life-FOREST CO2 (LIFE14 CCM/ES/001271), ALTERACLIM (CGL2015-69773-C2-1-P), INERTIA
(PID2019-111332RB-C22-BDV), CEHYRFO-MED (CGL2017-86839-C3-2-R), DEHESACLIM (IB16185),
RESILIENTFORESTS (LIFE17 CCA/ES/000063), Rhysotto (PID2019-106583RB-I00), AGL2017-83828-
C2-2-R, RTI2018-096884-B-C31, ESPAS (CGL2015-65569-R), and caRRRascal (RTI2018-095037-B-I00)
: We thank the financial support from the “Ministerio de Ciencia e Innovación
-Redes de Investigación 2018, Programa Estatal de Generación de Conocimiento y Fortalecimiento
Científico y Tecnológico del Sistema de I + D + I
Optimally robust shortcuts to population inversion in two-level quantum systems
We examine the stability versus different types of perturbations of recently
proposed shortcuts-to-adiabaticity to speed up the population inversion of a
two-level quantum system. We find optimally robust processes using invariant
based engineering of the Hamiltonian. Amplitude noise and systematic errors
require different optimal protocols.Comment: 17 pages, 7 figure
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