We present experiments on ensemble cavity quantum electrodynamics with cold potassium atoms in a high-finesse ring cavity. Potassium-39 atoms are cooled in a two-dimensional magneto-optical trap and transferred to a three-dimensional trap which intersects the cavity mode. The apparatus is described in detail and the first observations of strong coupling with potassium atoms are presented. Collective strong coupling of atoms and light is demonstrated via the splitting of the cavity transmission spectrum and the avoided crossing of the normal modes.
We study electromagnetically induced transparency (EIT) in a heated potassium vapor cell, using a simple optical setup with a single free-running diode laser and an acousto-optic modulator. Despite the fact that the Doppler width is comparable to the ground state hyperfine splitting, transparency windows with deeply sub-natural line widths and large group indices are obtained. A longitudinal magnetic field is used to split the EIT feature and induce magneto-optical anisotropy. Using the beat note between co-propagating coupling and probe beams, we perform a heterodyne measurement of the circular dichroism (and therefore birefringence) of the EIT medium. The observed spectra reveal that lin‖lin polarizations lead to greater anisotropy than lin⊥lin. A simplified ‖analytical model encompassing sixteen Zeeman states and eighteen Λ subsytems reproduces the experimental observations.
We discuss the prospects for enhancing absorption and scattering of light
from a weakly coupled atom in a high-finesse optical cavity by adding a medium
with large, positive group index of refraction. The slow-light effect is known
to narrow the cavity transmission spectrum and increase the photon lifetime,
but the quality factor of the cavity may not be increased in a metrologically
useful sense. Specifically, detection of the weakly coupled atom through either
cavity ringdown measurements or the Purcell effect fails to improve with the
addition of material slow light. A single-atom model of the dispersive medium
helps elucidate why this is the case.Comment: 11 pages, 4 figures; QuTiP python file included. This version:
changed title and added several references; results are unchanged. Accepted
for open access publication in a special issue of Journal of Modern Optics in
memory of Prof Danny Segal. Publisher's version available at
http://dx.doi.org/10.1080/09500340.2017.138451
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