Master´s Thesis Defense by Signe Markussen

Trapping and cooling of cesium atoms in an optical nanofiber trap

An optical nanofiber trap acts as an efficient interface between an ensemble
of about 1000 atoms and light in a well-defined optical mode. This makes
nanofiber traps a suitable platform for various interesting studies in the
fields of atomic physics and quantum optics.
Due to the strong spatial gradients in the evanescent field around the
nanofiber waist, thermal motion of the atoms can induce noise in the coupling
between light and atoms, and this effect has created limitations for
several experiments. This motivates the need for cooling of atomic motion
in nanofiber trapped ensembles.
In this thesis, we produce, characterize and install a new nanofiber in
the existing nanofiber trap setup in the Quantop group at the Niels Bohr
Institute, as a replacement for a broken fiber. Furthermore, we implement
a degenerate Raman cooling scheme on the fiber in the setup. We find that
by cooling, we can increase the lifetime of atoms in the trap from 24 ms
to 128 ms. A Raman spectroscopy scheme is adapted for temperature
measurements on the stretched levels of cesium, and with this method we
estimate a temperature decrease from 21(3) µK to 13(2) µK.