3 research outputs found
Rydberg states of helium in electric and magnetic fields of arbitrary relative orientation
A spectroscopic study of Rydberg states of helium ( = 30 and 45) in
magnetic, electric and combined magnetic and electric fields with arbitrary
relative orientations of the field vectors is presented. The emphasis is on two
special cases where (i) the diamagnetic term is negligible and both
paramagnetic Zeeman and Stark effects are linear ( = 30, 120 mT and
= 0 - 78 V/cm ), and (ii) the diamagnetic term is dominant and the Stark
effect is linear ( = 45, = 277 mT and = 0 - 8 V/cm). Both cases
correspond to regimes where the interactions induced by the electric and
magnetic fields are much weaker than the Coulomb interaction, but much stronger
than the spin-orbit interaction. The experimental spectra are compared to
spectra calculated by determining the eigenvalues of the Hamiltonian matrix
describing helium Rydberg states in the external fields. The spectra and the
calculated energy-level diagrams in external fields reveal avoided crossings
between levels of different values and pronounced -mixing effects at
all angles between the electric and magnetic field vectors other than 0. These
observations are discussed in the context of the development of a method to
generate dense samples of cold atoms and molecules in a magnetic trap following
Rydberg-Stark deceleration.Comment: 16 pages, 18 figure
Manipulating Rydberg atoms close to surfaces at cryogenic temperatures
Helium atoms in Rydberg states have been manipulated coherently with
microwave radiation pulses near a gold surface and near a superconducting NbTiN
surface at a temperature of . The experiments were carried out with
a skimmed supersonic beam of metastable helium atoms excited with laser radiation to
Rydberg levels with principal quantum number between and . The
separation between the cold surface and the center of the collimated beam is
adjustable down to . Short-lived Rydberg levels
were coherently transferred to the long-lived state to avoid
radiative decay of the Rydberg atoms between the photoexcitation region and the
region above the cold surfaces. Further coherent manipulation of the
Rydberg levels with pulsed microwave radiation above the surfaces
enabled measurements of stray electric fields and allowed us to study the
decoherence of the atomic ensemble. Adsorption of residual gas onto the
surfaces and the resulting slow build-up of stray fields was minimized by
controlling the temperature of the surface and monitoring the partial pressures
of HO, N, O and CO in the experimental chamber during the
cool-down. Compensation of the stray electric fields to levels below was achieved over a region of along the
beam-propagation direction which, for the beam
velocity, implies the possibility to preserve the coherence of the atomic
sample for several microseconds above the cold surfaces.Comment: 12 pages, 10 figure