Measuring fluorescence into a nanofiber by observing field quadrature noise.

We perform balanced homodyne detection of the electromagnetic field in a single-mode tapered optical nanofiber surrounded by rubidium atoms in a magneto-optical trap. Resonant fluorescence of atoms into the nanofiber mode manifests itself as increased quantum noise of the field quadratures. The autocorrelation function of the homodyne detector's output photocurrent exhibits exponential fall-off with a decay time constant of 26.3±0.6 ns, which is consistent with the theoretical expectation under our experimental conditions. To the best of our knowledge, this is the first experiment in which fluorescence into a tapered optical nanofiber has been observed and measured by balanced optical homodyne detection.

Note: a monolithic filter cavity for experiments in quantum optics.

By applying a high-reflectivity dielectric coating on both sides of a commercial plano-convex lens, we produce a stable monolithic Fabry-Perot cavity suitable for use as a narrow band filter in quantum optics experiments. The resonant frequency is selected by means of thermal expansion. Owing to the long term mechanical stability, no optical locking techniques are required. We characterize the cavity performance as an optical filter, obtaining a 45dB suppression of unwanted modes while maintaining a transmission of 60%.