2,362 research outputs found
Prospects for measuring the electric dipole moment of the electron using electrically trapped polar molecules
Heavy polar molecules can be used to measure the electric dipole moment of
the electron, which is a sensitive probe of physics beyond the Standard Model.
The value is determined by measuring the precession of the molecule's spin in a
plane perpendicular to an applied electric field. The longer this precession
evolves coherently, the higher the precision of the measurement. For molecules
in a trap, this coherence time could be very long indeed. We evaluate the
sensitivity of an experiment where neutral molecules are trapped electrically,
and compare this to an equivalent measurement in a molecular beam. We consider
the use of a Stark decelerator to load the trap from a supersonic source, and
calculate the deceleration efficiency for YbF molecules in both strong-field
seeking and weak-field seeking states. With a 1s holding time in the trap, the
statistical sensitivity could be ten times higher than it is in the beam
experiment, and this could improve by a further factor of five if the trap can
be loaded from a source of larger emittance. We study some effects due to field
inhomogeneity in the trap and find that rotation of the electric field
direction, leading to an inhomogeneous geometric phase shift, is the primary
obstacle to a sensitive trap-based measurement.Comment: 22 pages, 7 figures, prepared for Faraday Discussion 14
Stochastic multi-channel lock-in detection
High-precision measurements benefit from lock-in detection of small signals.
Here we discuss the extension of lock-in detection to many channels, using
mutually orthogonal modulation waveforms, and show how the the choice of
waveforms affects the information content of the signal. We also consider how
well the detection scheme rejects noise, both random and correlated. We address
the particular difficulty of rejecting a background drift that makes a
reproducible offset in the output signal and we show how a systematic error can
be avoided by changing the waveforms between runs and averaging over many runs.
These advances made possible a recent measurement of the electron's electric
dipole moment.Comment: 11 pages, 3 figure
A high quality, efficiently coupled microwave cavity for trapping cold molecules
We characterize a Fabry-Perot microwave cavity designed for trapping atoms
and molecules at the antinode of a microwave field. The cavity is fed from a
waveguide through a small coupling hole. Focussing on the compact resonant
modes of the cavity, we measure how the electric field profile, the cavity
quality factor, and the coupling efficiency, depend on the radius of the
coupling hole. We measure how the quality factor depends on the temperature of
the mirrors in the range from 77 to 293K. The presence of the coupling hole
slightly changes the profile of the mode, leading to increased diffraction
losses around the edges of the mirrors and a small reduction in quality factor.
We find the hole size that maximizes the intra-cavity electric field. We
develop an analytical theory of the aperture-coupled cavity that agrees well
with our measurements, with small deviations due to enhanced diffraction
losses. We find excellent agreement between our measurements and
finite-difference time-domain simulations of the cavity.Comment: 16 pages, 8 figure
Probing the electron EDM with cold molecules
We present progress towards a new measurement of the electron electric dipole
moment using a cold supersonic beam of YbF molecules. Data are currently being
taken with a sensitivity of . We
therefore expect to make an improvement over the Tl experiment of Commins'
group, which currently gives the most precise result. We discuss the systematic
and statistical errors and comment on the future prospect of making a
measurement at the level of .Comment: 8 pages, 6 figures, proceedings of ICAP 200
Characterization of a cryogenic beam source for atoms and molecules
We present a combined experimental and theoretical study of beam formation
from a cryogenic buffer gas cell. Atoms and molecules are loaded into the cell
by laser ablation of a target, and are cooled and swept out of the cell by a
flow of cold helium. We study the thermalization and flow dynamics inside the
cell and measure how the speed, temperature, divergence and extraction
efficiency of the beam are influenced by the helium flow. We use a finite
element model to simulate the flow dynamics and use the predictions of this
model to interpret our experimental results.Comment: 10 pages, 14 figure
A robust floating nanoammeter
A circuit capable of measuring nanoampere currents while floating at voltages
up to at least 25kV is described. The circuit relays its output to ground
potential via an optical fiber. We particularly emphasize the design and
construction techniques which allow robust operation in the presence of high
voltage spikes and discharges.Comment: 5 pages, 2 figure
Prospects for the measurement of the electron electric dipole moment using YbF
We discuss an experiment underway at Imperial College London to measure the
permanent electric dipole moment (EDM) of the electron using a molecular beam
of YbF. We describe the measurement method, which uses a combination of laser
and radiofrequency resonance techniques to detect the spin precession of the
YbF molecule in a strong electric field. We pay particular attention to the
analysis scheme and explore some of the possible systematic effects which might
mimic the EDM signal. Finally, we describe technical improvements which should
increase the sensitivity by more than an order of magnitude over the current
experimental limit.Comment: 6 pages, 2 figure
Atom chip for BEC interferometry
We have fabricated and tested an atom chip that operates as a matter wave interferometer. In this communication we describe the fabrication of the chip by ion-beam milling of gold evaporated onto a silicon substrate. We present data on the quality of the wires, on the current density that can be reached in the wires and on the smoothness of the magnetic traps that are formed. We demonstrate the operation of the interferometer, showing that we can coherently split and recombine a Bose–Einstein condensate with good phase stability
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