Abstract Light guided by an optical nanofibre has a very steep evanescent field gradient extending from the fibre surface. This gradient can be exploited to drive electric quadrupole transitions in nearby quantum emitters. In this paper, we report on the observation of the 5S1/2 → 4D3/2 electric quadrupole transition at 516.6 nm (in vacuum) in laser-cooled 87Rb atoms using only a few μW of laser power propagating through an optical nanofibre embedded in the atom cloud. This work extends the range of applications for optical nanofibres in atomic physics to include more fundamental tests such as high-precision measurements of parity non-conservation.
Hyperfine-structure-resolved absorption spectra of the $6\phantom{\rule{0.2em}{0ex}}^{2}S_{1∕2}\ensuremath{\rightarrow}5\phantom{\rule{0.2em}{0ex}}^{2}D_{5∕2}$ of cesium atoms have been observed with a temperature-controlled cell and a diode laser. From a comparison with the absorption of the
D2 transition at the same atom density range, the oscillator strength of the electric quadrupole transition was determined to be $(4.69\ifmmode\pm\else\textpm\fi{}0.05)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$. Reflection spectra of the same transition have also been observed in the partial and total reflection regimes with a reflection cell. An increase in the apparent oscillator strength was observed for total reflection with an increase in the angle of incidence, by a factor up to 1.5 at ${\ensuremath{\theta}}_{c}+83.8\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$ and 2.4 at ${\ensuremath{\theta}}_{c}+107.5\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$ for
s and
p polarizations, respectively, where ${\ensuremath{\theta}}_{c}$ is the critical angle. The observed enhancement is ascribed to the incidence-angle-dependent wave vector and polarization vector of the evanescent wave.
A single Sr+ atom was confined in a radio-frequency quadrupole trap and laser cooled with resonant laser light. Examination of the transition Doppler profile indicated an ion kinetic temperature of less than 500 mK. Quantum jumps into and out of the metastable 4d(2)D(5/2) level were observed by laser excitation on the electric-quadrupole-allowed transition from the ground state at 674 nm. The dark and bright periods in the strong fluorescence showed variations owing to the applied driving field on the electric-quadrupole transition. These results provide an improved determination of tau = 372 +/- 25 msec for the natural metastable-state lifetime.