338 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
Franck-Condon Factors and Radiative Lifetime of the A^{2}\Pi_{1/2} - X^{2}\Sigma^{+} Transition of Ytterbium Monoflouride, YbF
The fluorescence spectrum resulting from laser excitation of the
A^{2}\Pi_{1/2} - X^{2}\Sigma^{+} (0,0) band of ytterbium monofluoride, YbF, has
been recorded and analyzed to determine the Franck-Condon factors. The measured
values are compared with those predicted from Rydberg-Klein-Rees (RKR)
potential energy curves. From the fluorescence decay curve the radiative
lifetime of the A^{2}\Pi_{1/2} state is measured to be 28\pm2 ns, and the
corresponding transition dipole moment is 4.39\pm0.16 D. The implications for
laser cooling YbF are discussed.Comment: 5 pages, 5 figure
Optical cycling in polyatomic molecules with complex hyperfine structure
We have developed and demonstrated a scheme to achieve rotationally-closed
photon cycling in polyatomic molecules with complex hyperfine structure and
sensitivity to hadronic symmetry violation, specifically YbOH and
YbOH. We calculate rotational branching ratios for spontaneous decay
and identify repumping schemes which use electro-optical modulators (EOMs) to
address the hyperfine structure. We demonstrate our scheme by cycling photons
in a molecular beam and verify that we have achieved rotationally-closed
cycling by measuring optical pumping into unaddressed vibrational states. Our
work makes progress along the path toward utilizing photon cycling for state
preparation, readout, and laser cooling in precision measurements of polyatomic
molecules with complex hyperfine structure.Comment: 10 pages, 7 figure
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.
U-Note: Capture the Class and Access it Everywhere
We present U-Note, an augmented teaching and learning system leveraging the
advantages of paper while letting teachers and pupils benefit from the richness
that digital media can bring to a lecture. U-Note provides automatic linking
between the notes of the pupils' notebooks and various events that occurred
during the class (such as opening digital documents, changing slides, writing
text on an interactive whiteboard...). Pupils can thus explore their notes in
conjunction with the digital documents that were presented by the teacher
during the lesson. Additionally, they can also listen to what the teacher was
saying when a given note was written. Finally, they can add their own comments
and documents to their notebooks to extend their lecture notes. We interviewed
teachers and deployed questionnaires to identify both teachers and pupils'
habits: most of the teachers use (or would like to use) digital documents in
their lectures but have problems in sharing these resources with their pupils.
The results of this study also show that paper remains the primary medium used
for knowledge keeping, sharing and editing by the pupils. Based on these
observations, we designed U-Note, which is built on three modules. U-Teach
captures the context of the class: audio recordings, the whiteboard contents,
together with the web pages, videos and slideshows displayed during the lesson.
U-Study binds pupils' paper notes (taken with an Anoto digital pen) with the
data coming from U-Teach and lets pupils access the class materials at home,
through their notebooks. U-Move lets pupils browse lecture materials on their
smartphone when they are not in front of a computer
The pure rotational spectrum of YbOH
The pure rotational spectrum of YbOH has been recorded and analyzed to produce fine and magnetic hyperfine parameters for the X^2ÎŁ^+(0,0,0) state. These parameters are compared with those determined from the optical study [Melville and Coxon, J. Chem. Phys.115, 6974-6978 (2001)] and with the values for YbF [Dickinson et al.115, 6979-6989 (2001)]. The results support the existence of an unobserved perturbing state near the A^2Î _(1/2) state, similar to that previously found in YbF. The precisely determining parameters lays the foundation for laser cooling YbOH, which will aid in the search for new physics beyond the standard model
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.
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