18,553 research outputs found

### Creating ultracold molecules by collisions with ultracold rare gas atoms in an optical trap

We study collisions of para-H$_2$ with five rare gas atomic species (He, Ne,
Ar, Kr and Xe) over the range from 1 K to 1 $\mu$ K and evaluate the
feasibility of sympathetic cooling H$_2$ with ultracold ground state rare gas
atoms co-trapped within a deep optical trap. Collision cross-sections over this
large temperature range show that all of these species could be used to cool
H$_2$ to ultracold temperatures and that argon and helium are the most
promising species for future experiments.Comment: 5 pages, 1 figure, 1 table, submitted for publicatio

### Super-resolution imaging of a low frequency levitated oscillator

We describe the measurement of the secular motion of a levitated nanoparticle
in a Paul trap with a CMOS camera. This simple method enables us to reach
signal-to-noise ratios as good as 10$^{6}$ with a displacement sensitivity
better than 10$^{-16}\,m^{2}$/Hz. This method can be used to extract trap
parameters as well as the properties of the levitated particles. We demonstrate
continuous monitoring of the particle dynamics on timescales of the order of
weeks. We show that by using the improvement given by super-resolution imaging,
a significant reduction in the noise floor can be attained, with an increase in
the bandwidth of the force sensitivity. This approach represents a competitive
alternative to standard optical detection for a range of low frequency
oscillators where low optical powers are require

### Testing Wavefunction Collapse Models using Parametric Heating of a Trapped Nanosphere

We propose a mechanism for testing the theory of collapse models such as
continuous spontaneous localization (CSL) by examining the parametric heating
rate of a trapped nanosphere. The random localizations of the centre-of-mass
for a given particle predicted by the CSL model can be understood as a
stochastic force embodying a source of heating for the nanosphere. We show that
by utilising a Paul trap to levitate the particle and optical cooling, it is
possible to reduce environmental decoherence to such a level that CSL dominates
the dynamics and contributes the main source of heating. We show that this
approach allows measurements to be made on the timescale of seconds, and that
the free parameter $\lambda_{\rm CSL}$ which characterises the model ought to
be testable to values as low as $10^{-12}$ Hz.Comment: 5 pages, 4 figure

### Simultaneous cooling of coupled mechanical oscillators using whispering gallery mode resonances

We demonstrate simultaneous center-of-mass cooling of two coupled
oscillators, consisting of a microsphere-cantilever and a tapered optical
fiber. Excitation of a whispering gallery mode (WGM) of the microsphere, via
the evanescent field of the taper, provides a transduction signal that
continuously monitors the relative motion between these two microgram objects
with a sensitivity of 3 pm. The cavity enhanced optical dipole force is used to
provide feedback damping on the motion of the micron-diameter taper, whereas a
piezo stack is used to damp the motion of the much larger (up to $180\,\mu$m in
diameter), heavier (up to $1.5\times 10^{-7}\,$kg) and stiffer
microsphere-cantilever. In each feedback scheme multiple mechanical modes of
each oscillator can be cooled, and mode temperatures below 10 K are reached for
the dominant mode, consistent with limits determined by the measurement noise
of our system. This represents stabilization on the picometer level and is the
first demonstration of using WGM resonances to cool the mechanical modes of
both the WGM resonator and its coupling waveguide.Comment: 10 pages, 8 figure

### An Alternative Parameterization of R-matrix Theory

An alternative parameterization of R-matrix theory is presented which is
mathematically equivalent to the standard approach, but possesses features
which simplify the fitting of experimental data. In particular there are no
level shifts and no boundary-condition constants which allows the positions and
partial widths of an arbitrary number levels to be easily fixed in an analysis.
These alternative parameters can be converted to standard R-matrix parameters
by a straightforward matrix diagonalization procedure. In addition it is
possible to express the collision matrix directly in terms of the alternative
parameters.Comment: 8 pages; accepted for publication in Phys. Rev. C; expanded Sec. IV,
added Sec. VI, added Appendix, corrected typo

### New broad 8Be nuclear resonances

Energies, total and partial widths, and reduced width amplitudes of 8Be
resonances up to an excitation energy of 26 MeV are extracted from a coupled
channel analysis of experimental data. The presence of an extremely broad J^pi
= 2^+ ``intruder'' resonance is confirmed, while a new 1^+ and very broad 4^+
resonance are discovered. A previously known 22 MeV 2^+ resonance is likely
resolved into two resonances. The experimental J^pi T = 3^(+)? resonance at 22
MeV is determined to be 3^-0, and the experimental 1^-? (at 19 MeV) and 4^-?
resonances to be isospin 0.Comment: 16 pages, LaTe

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