Abstract
We study an integrated silicon photonic chip, composed of several sub-wavelength ridge waveguides, and immersed in a micro-cell with rubidium vapor. Employing two-photon excitation, including a telecom wavelength, we observe that the waveguide transmission spectrum gets modified when the photonic mode is coupled to rubidium atoms through its evanescent tail. Due to the enhanced electric field in the waveguide cladding, the atomic transition can be saturated at a photon number ≈80 times less than a free-propagating beam case. The non-linearity of the atom-clad Si-waveguide is about 4 orders of magnitude larger than the maximum achievable value in doped Si photonics. The measured spectra corroborate well with a generalized effective susceptibility model that includes the Casimir-Polder potentials, due to the dielectric surface, and the transient interaction between flying atoms and the evanescent waveguide mode. This work paves the way towards a miniaturized, low-power, and integrated hybrid atomic-photonic system compatible with CMOS technologies.
Highlights
The ability to control and exploit light-matter interactions holds substantial promises for discovering novel phenomena and technological applications
Employing two-photon excitation, including a telecom wavelength, we observe that the waveguide transmission spectrum gets modified when the photonic mode is coupled to rubidium atoms through its evanescent tail
From the development of quantum theory, to the state-of-the-art photonic sensors and circuits, novel kinds of light-matter interactions have always opened the door to new fundamental insights and technologies, with interdisciplinary implications reaching beyond physics
Summary
The ability to control and exploit light-matter interactions holds substantial promises for discovering novel phenomena and technological applications. Combining nano-photonics and atomic physics has promising potentials for devising novel atom-light interaction schemes as well as new quantum hybrid systems benefiting from the best of both worlds. A recent attempt to increase the coupling strength between atoms and photons benefits from tightly confined mode of a sub-wavelength slot waveguide [39]. In spite of less precision and control in thermal vapor cells, their lower technical complexities and better compatibility with integration, still make thermal atoms interesting candidates for realizing non-classical light sources [40], small-scale atomic clocks [41], and quantum memories [42] as some of the major building blocks of a hybrid atom-nanophotonic network. By systematic measurement of the absorption linewidth at different telecom laser powers, even down to the single photon level, we investigated the effect of tight-mode confinement of the sub-wavelength waveguide via a noticeable reduction of the saturation power. The substantial reduction of the required power for inducing optical non-linearity makes this hybrid device an efficient candidate to produce non-classical light at the telecommunication band [45]
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