39 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 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
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
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
Stark shift of the state in YbF
We have measured the Stark shift of the
transition in YbF. We use a molecular beam triple resonance method, with two
laser transitions acting as pump and probe, assisted by an rf transition that
tags a single hyperfine transition of the X state. After subtracting the known
ground state Stark shift, we obtain a value of Hz/(V/cm) for
the static electric polarizability of the state . From
this we calculate a value D for the electric dipole moment of
the state.Comment: 3 pages, 2 figure
Pulsed beams as field probes for precision measurement
We describe a technique for mapping the spatial variation of static electric,
static magnetic, and rf magnetic fields using a pulsed atomic or molecular
beam. The method is demonstrated using a beam designed to measure the electric
dipole moment of the electron. We present maps of the interaction region,
showing sensitivity to (i) electric field variation of 1.5 V/cm at 3.3 kV/cm
with a spatial resolution of 15 mm; (ii) magnetic field variation of 5 nT with
25 mm resolution; (iii) radio-frequency magnetic field amplitude with 15 mm
resolution. This new diagnostic technique is very powerful in the context of
high-precision atomic and molecular physics experiments, where pulsed beams
have not hitherto found widespread application.Comment: 6 pages, 12 figures. Figures heavily compressed to comply with
arxiv's antediluvian file-size polic
Doppler-free laser spectroscopy of buffer gas cooled molecular radicals
We demonstrate Doppler-free saturated absorption spectroscopy of cold
molecular radicals formed by laser ablation inside a cryogenic buffer gas cell.
By lowering the temperature, congested regions of the spectrum can be
simplified, and by using different temperatures for different regions of the
spectrum a wide range of rotational states can be studied optimally. We use the
technique to study the optical spectrum of YbF radicals with a resolution of 30
MHz, measuring the magnetic hyperfine parameters of the electronic ground
state. The method is suitable for high resolution spectroscopy of a great
variety of molecules at controlled temperature and pressure, and is
particularly well-suited to those that are difficult to produce in the gas
phase.Comment: 11 pages, 4 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