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Over the past decades, alkali atoms have been the subject of intensive and diverse research, ranging from fundamental studies on ultra-cold atoms and Bose-Einstein condensates to technological applications. Since they possess only a single valance s-electron, the alkali atoms manifest a simple low-lying electronic structure compared to other atoms. Moreover, unlike conventional solid state systems their dispersion-free features make them an ideal candidate for sensing applications and referencing tasks. These two features have introduced alkali atoms as promising quantum emitters for the new paradigm of hybrid quantum optics and quantum electrodynamics. This new concept benefits from the existing integrated photonics technology for squeezing and confining the light in sub-wavelength scales to substantially enhance the light-atom interaction. The hybrid chip is envisioned to have light sources, waveguides, devices, and detectors to realize a complex quantum network down to a single photon level.
In this talk I will discuss about our recent theoretical and experimental works on atomic vapor spectroscopy in the vicinity of the plasmonic and nanophotonic devices. I start from a density matrix-based formalism describing the evolution of Rb vapor atomic levels, excited with an incoherent pump and coupled to a plasmonic lattice. When designed properly, the lattice plasmon mode efficiently captures the spontaneously emitted photons from the excited Rb atoms and a coherent coupling between the lattice mode and the atomic levels would occur. I will elaborate on the effect of pumping rate and decoherence on the steady state of the hybrid system and the feasibility of achieving a lasing state. In the second part of the talk I will present the results of our experiments on Rb vapor coupled to such a plasmonic lattice. Starting from the pumping mechanism, I describe the collisional scheme we employed to transfer the excited Rb atoms from (_^5)P_(3/2) to(_^5)P_(1/2) , hence achieving a population inversion between P and S levels and an optical gain at 795 nm, eventually. I present the experimental results of this atomic vapor interaction with a plasmonic lattice resonating at 795 nm. The spectroscopy of Rb cloud modified with tightly squeezed and enhanced field of the lattice plasmons shows the clear signature of Fano resonances in the passive gas, followed by amplified spontaneous emission in the active gas and the lasing at higher pumping powers. The results of this study would pave the way toward hybrid atom-quantum photonic chips.
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