Fast, low-loss all-optical phase modulation in warm rubidium vapour

Low-loss high-speed switches are an integral component of future photonic quantum technologies, with applications in state generation, multiplexing, and the implementation of quantum gates. Phase modulation is one method of achieving this switching, but existing optical phase modulators either achieve high bandwidth or low loss, but not both. We demonstrate fast ($100\mathrm{M}\mathrm{H}\mathrm{z}$ bandwidth), low-loss ($83\pm 2\mathrm{\%}$ transmission) phase shifting ($\mathrm{\Delta }\phi =(0.90\pm 0.05)\pi$) in a signal field, induced by a control field, and mediated by the two-photon $5S_{1\mathrm{/}2}\to 5P_{3\mathrm{/}2}\to 5D_{5\mathrm{/}2}$ transition in ${}^{87}\text{Rb}$ vapour. We discuss routes to enhance both performance and scalability for application to a range of quantum and classical technologies.