Vapor Spectroscopy and Extreme Nonlinear Optics via a Nano-fiber

When the diameter of an optical fiber is reduced below the wavelength of the light it carries, a significant portion of the optical field energy is carried by an evanescent field outside the fiber. Further reducing the diameter to about a quarter wavelength results in an evanescent field extending as far as five wavelengths, where practically all the mode energy is carried in this extended region. Nevertheless, this is still a bound mode and therefore can be guided for distances much longer than the Rayleigh range appropriate for such dimensions.

Atomic vapor in the evanescent field of such a nano-fiber interact with it in a unique way: the interaction is strong, has high optical depth and low transit time broadening. Here we realize this interaction and demonstrate lifetime-limited spectroscopy and extreme optical nonlinearity in a 200nm diameter nano-fiber carrying 780nm light in ⁸⁷Rb vapor.

Exciting atoms to high principle quantum numbers (so called “Rydberg atoms”) facilitates strong interactions over a scale compatible with the extent of the mode in the nano-fiber. Our system is thus ideally suited to utilize this effect for realizing quantum nonlinear optics [1] in hot atomic vapor. Such nonlinear response has been used to demonstrate novel states of light, a single photon transistor [2] and a single photon source at room temperature [3].

[1] Peyronel, T., Firstenberg, O., Liang, Q.Y., Hofferberth, S., Gorshkov, A.V., Pohl, T., Lukin, M.D. and Vuletić, V., 2012. Quantum nonlinear optics with single photons enabled by strongly interacting atoms. Nature, 488(7409), p.57.

[2] Gorniaczyk, H., Tresp, C., Schmidt, J., Fedder, H. and Hofferberth, S., 2014. Single-photon transistor mediated by interstate Rydberg interactions. Physical review letters, 113(5), p.053601.

[3] Ripka, F., Kübler, H., Löw, R. and Pfau, T., 2018. A room temperature single-photon source based on strongly interacting Rydberg atoms. arXiv preprint arXiv:1806.02120.