Coherent interactions between light and matter
In a recent study, Dr. Ofer Firstenberg and Prof. Barak Dayan introduced a new platform to explore light/matter interactions—one which employs a nanofiber-guided mode with a super-extended evanescent field, characterized by low transit-time broadening. This unique mode is achieved using a single-mode fiber, tapered down to a quarter of a wavelength.
The scientists worked together to fabricate an extremely thin optical fiber that supports a super-extended mode with a diameter as large as 13 times the optical wavelength, residing almost entirely outside the fiber and guided over thousands of wavelengths (5 mm)—all this to couple guided light to warm atomic vapor. This unique configuration balances between strong confinement of the photons and long interaction times with the thermal atoms, thereby enabling fast and coherent interactions (see Figure 2).
The researchers demonstrated narrow coherent resonances (tens of MHz) of electromagnetically induced transparency for signals at the single-photon level, and long relaxation times (10 nanoseconds) of atoms excited by the guided mode. The resulting platform is particularly suitable for observing quantum nonlinear optics phenomena (Optica 2021).
(Image: Super-extended evanescent field of a nanofiber interacting with atomic vapor. (a) Illustration of the extent of an optical mode surrounding a thin optical fiber. (b) Mode field diameter as a function of fiber diameter. Blue and red circles mark the parameters of the two fibers shown in (a). Dashed black line marks the physical fiber dimensions. (c) Calculated Doppler-free absorption spectra for rubidium (Rb) vapor in the evanescent field silica fibers (n=1.45. The effect of transit-time broadening is apparent.)