406 research outputs found
Modeling magneto-optical trapping of CaF molecules
Magneto-optical trapping forces for molecules are far weaker than for alkali
atoms because the photon scattering rate is reduced when there are multiple
ground states, and because of optical pumping into dark states. The force is
further reduced when the upper state has a much smaller Zeeman splitting than
the lower state. We use a rate model to estimate the strength of the trapping
and damping forces in a magneto-optical trap (MOT) of CaF molecules, using
either the A - X transition or the
B - X transition. We identify a new mechanism
of magneto-optical trapping that arises when, in each beam of the MOT, two
laser components with opposite polarizations and different detunings address
the same transition. This mechanism produces a strong trapping force even when
the upper state has little or no Zeeman splitting. It is the main mechanism
responsible for the trapping force when the A -
X transition is used.Comment: 8 pages, 6 figures. Supplemental Material containing 7 figure
Obstructions to Fibering a Manifold
Given a map f: M \to M of closed topological manifolds we define torsion
obstructions whose vanishing is a necessary condition for f being homotopy
equivalent to a projection of a locally trivial fiber bundle. If N = S^1, these
torsion obstructions are identified with the ones due to Farrell.
We have changed the exposition according to the comments of the referee and
corrected some typos. The paper will appear in Geometriae Dedicata.Comment: 33 page
Quantum chaos in open systems: a quantum state diffusion analysis
Except for the universe, all quantum systems are open, and according to
quantum state diffusion theory, many systems localize to wave packets in the
neighborhood of phase space points. This is due to decoherence from the
interaction with the environment, and makes the quasiclassical limit of such
systems both more realistic and simpler in many respects than the more familiar
quasiclassical limit for closed systems. A linearized version of this theory
leads to the correct classical dynamics in the macroscopic limit, even for
nonlinear and chaotic systems. We apply the theory to the forced, damped
Duffing oscillator, comparing the numerical results of the full and linearized
equations, and argue that this can be used to make explicit calculations in the
decoherent histories formalism of quantum mechanics.Comment: 18 pages standard LaTeX + 9 figures; extensively trimmed; to appear
in J. Phys.
Branching Ratios, Radiative Lifetimes and Transition Dipole Moments for YbOH
Medium resolution (Δν~ 3 GHz) laser-induced fluorescence (LIF) excitation spectra of a rotationally cold sample of YbOH in the 17300-17950 cm⁻¹ range have been recorded using two-dimensional (excitation and dispersed fluorescence) spectroscopy. High resolution (Δλ~ 0.65 nm) dispersed laser induced fluorescence (DLIF) spectra and radiative decay curves of numerous bands detected in the medium resolution LIF excitation spectra were recorded. The vibronic energy levels of the X²Σ state were predicted using a discrete variable representation approach and compared with observations. The radiative decay curves were analyzed to produce fluorescence lifetimes. DLIF spectra resulting from high resolution (Δν < 10 MHz) LIF excitation of individual low-rotational lines in the A²Π_(1/2)(000)-X²Σ((000), A²Π_(1/2)(100)-X²Σ((000), and [17.73]Ω=0.5-X²Σ((000) bands were also recorded. The DLIF spectra were analyzed to determine branching ratios which were combined with radiative lifetimes to obtain transition dipole moments. The implications for laser cooling and trapping of YbOH are discussed
Quantum trajectories for Brownian motion
We present the stochastic Schroedinger equation for the dynamics of a quantum
particle coupled to a high temperature environment and apply it the dynamics of
a driven, damped, nonlinear quantum oscillator. Apart from an initial slip on
the environmental memory time scale, in the mean, our result recovers the
solution of the known non-Lindblad quantum Brownian motion master equation. A
remarkable feature of our approach is its localization property: individual
quantum trajectories remain localized wave packets for all times, even for the
classically chaotic system considered here, the localization being stronger the
smaller .Comment: 4 pages, 3 eps figure
Continuous stochastic Schrodinger equations and localization
The set of continuous norm-preserving stochastic Schrodinger equations
associated with the Lindblad master equation is introduced. This set is used to
describe the localization properties of the state vector toward eigenstates of
the environment operator. Particular focus is placed on determining the
stochastic equation which exhibits the highest rate of localization for wide
open systems. An equation having such a property is proposed in the case of a
single non-hermitian environment operator. This result is relevant to numerical
simulations of quantum trajectories where localization properties are used to
reduce the number of basis states needed to represent the system state, and
thereby increase the speed of calculation.Comment: 18 pages in LaTeX + 6 figures (postscript), uses ioplppt.sty. To
appear in J. Phys.
Manifesto for Digital Social Touch in Crisis
This qualitative exploratory research paper presents a Manifesto for Digital Social Touch in Crisis - a provocative call to action to designers, developers and researchers to rethink and reimagine social touch through a deeper engagement with the social and sensory aspects of touch. This call is motivated by concerns that social touch is in a crisis signaled by a decline in social touch over the past 2 decades, the problematics of inappropriate social touch, and the well documented impact of a lack of social touch on communication, relationships, and well-being and health. These concerns shape how social touch enters the digital realm and raise questions for how and when the complex space of social touch is mediated by technologies, as well the societal implications. The paper situates the manifesto in the key challenges facing haptic designers and developers identified through a series of interdisciplinary collaborative workshops with participants from computer science, design, engineering, HCI and social science from both within industry and academia, and the research literature on haptics. The features and purpose of the manifesto form are described, along with our rationale for its use, and the method of the manifesto development. The starting points, opportunities and challenges, dominant themes and tensions that shaped the manifesto statements are then elaborated on. The paper shows the potential of the manifesto form to bridge between HCI, computer science and engineers, and social scientists on the topic of social touch
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