721 research outputs found
General variational approach to nuclear-quadrupole coupling in rovibrational spectra of polyatomic molecules
A general algorithm for computing the quadrupole-hyperfine effects in the
rovibrational spectra of polyatomic molecules is presented for the case of
ammonia (NH). The method extends the general variational approach TROVE by
adding the extra term in the Hamiltonian that describes the nuclear quadrupole
coupling, with no inherent limitation on the number of quadrupolar nuclei in a
molecule. We applied the new approach to compute the
nitrogen-nuclear-quadrupole hyperfine structure in the rovibrational spectrum
of NH. These results agree very well with recent experimental spectroscopic
data for the pure rotational transitions in the ground vibrational and
states, and the rovibrational transitions in the , , ,
and bands. The computed hyperfine-resolved rovibrational spectrum
of ammonia will be beneficial for the assignment of experimental rovibrational
spectra, further detection of ammonia in interstellar space, and studies of the
proton-to-electron mass variation
29Si Hyperfine Structure of the E'_\alpha Center in Amorphous Silicon Dioxide
We report a study by electron paramagnetic resonance (EPR) on the E'_\alpha
point defect in amorphous silicon dioxide (a-SiO2). Our experiments were
performed on gamma-ray irradiated oxygen-deficient materials and pointed out
that the 29Si hyperfine structure of the E'_alpha consists in a pair of lines
split by 49 mT. On the basis of the experimental results a microscopic model is
proposed for the E'_alpha center, consisting in a hole trapped in an oxygen
vacancy with the unpaired electron sp3 orbital pointing away from the vacancy
in a back-projected configuration and interacting with an extra oxygen atom of
the a-SiO2 matrix.Comment: 4 page
A note on Turán type and mean inequalities for the Kummer function
AbstractTurán-type inequalities for combinations of Kummer functions involving Φ(a±ν,c±ν,x) and Φ(a,c±ν,x) have been recently investigated in [Á. Baricz, Functional inequalities involving Bessel and modified Bessel functions of the first kind, Expo. Math. 26 (3) (2008) 279–293; M.E.H. Ismail, A. Laforgia, Monotonicity properties of determinants of special functions, Constr. Approx. 26 (2007) 1–9]. In the current paper, we resolve the corresponding Turán-type and closely related mean inequalities for the additional case involving Φ(a±ν,c,x). The application to modeling credit risk is also summarized
Opto-Electrical Cooling of Polar Molecules
We present an opto-electrical cooling scheme for polar molecules based on a
Sisyphus-type cooling cycle in suitably tailored electric trapping fields.
Dissipation is provided by spontaneous vibrational decay in a closed level
scheme found in symmetric-top rotors comprising six low-field-seeking
rovibrational states. A generic trap design is presented. Suitable molecules
are identified with vibrational decay rates on the order of 100Hz. A simulation
of the cooling process shows that the molecular temperature can be reduced from
1K to 1mK in approximately 10s. The molecules remain electrically trapped
during this time, indicating that the ultracold regime can be reached in an
experimentally feasible scheme
Matrix algorithm for solving Schroedinger equations with position-dependent mass or complex optical potentials
We represent low dimensional quantum mechanical Hamiltonians by moderately
sized finite matrices that reproduce the lowest O(10) boundstate energies and
wave functions to machine precision. The method extends also to Hamiltonians
that are neither Hermitian nor PT symmetric and thus allows to investigate
whether or not the spectra in such cases are still real. Furthermore, the
approach is especially useful for problems in which a position-dependent mass
is adopted, for example in effective-mass models in solid-state physics or in
the approximate treatment of coupled nuclear motion in molecular physics or
quantum chemistry. The performance of the algorithm is demonstrated by
considering the inversion motion of different isotopes of ammonia molecules
within a position-dependent-mass model and some other examples of one- and
two-dimensional Hamiltonians that allow for the comparison to analytical or
numerical results in the literature.Comment: 10 pages, 5 figures. Several clarifications in the text and new sect.
IV.G. Version to appear in Phys. Rev.
Improved spatial separation of neutral molecules
We have developed and experimentally demonstrated an improved electrostatic
deflector for the spatial separation of molecules according to their
dipole-moment-to-mass ratio. The device features a very open structure that
allows for significantly stronger electric fields as well as for stronger
deflection without molecules crashing into the device itself. We have
demonstrated its performance using the prototypical OCS molecule and we discuss
opportunities regarding improved quantum-state-selectivity for complex
molecules and the deflection of unpolar molecules.Comment: 6 figure
On Quantum State Observability and Measurement
We consider the problem of determining the state of a quantum system given
one or more readings of the expectation value of an observable. The system is
assumed to be a finite dimensional quantum control system for which we can
influence the dynamics by generating all the unitary evolutions in a Lie group.
We investigate to what extent, by an appropriate sequence of evolutions and
measurements, we can obtain information on the initial state of the system. We
present a system theoretic viewpoint of this problem in that we study the {\it
observability} of the system. In this context, we characterize the equivalence
classes of indistinguishable states and propose algorithms for state
identification
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