Interaction of light with a single atom in the strong focusing regime

Abstract

We consider the near-resonant interaction between a single atom and a focused light mode, where a single atom localized at the focus of a lens can scatter a significant fraction of light. Complementary to previous experiments on extinction and phase shift effects of a single atom, we report here on the measurement of coherently backscattered light. The strength of the observed effect suggests combining strong focusing with the well-established methods of cavity QED. We consider theoretically a nearly concentric cavity, which should allow for a strongly focused optical mode. Simple estimates show that in a such case one can expect a significant single photon Rabi frequency. This opens new perspectives and a possibility to scale up the system consisting of many atom+cavity nodes for quantum networking due to a significant technical simplification of the atom-light interfaces.

Light–matter interaction in free space

“…The first group of experiments tackles the problem of efficient elastic scattering of a weak continuous wave (cw) laser beam [17–23]. Here, ‘weak’ means that the incident coherent state has an amplitude that is low enough to prevent an appreciable population and thus saturation of the atom's excited state.…”

Narrow Band Source of Transform-Limited Photon Pairs via Four-Wave Mixing in a Cold Atomic Ensemble

“…We also demonstrate the thermal statistics of the signal and idler photons from a direct autocorrelation measurement. Beyond correlated photon pair preparation, this scheme can also provide polarization entangled photons by an appropriate choice of pump polarization [24,26], which can be used to implement entanglement swapping and other quantum communication protocols with single atoms [40,41], ions [42], or atomic ensembles. Furthermore, the long coherence time of our idler photon heralded by the ''click'' detection of the signal photon by an avalanche photodetector enables electric field quadrature measurements of the idler photon by homodyne detection using currently available fast photodetectors [43,44].…”

Diffraction-limited Fabry–Perot cavity in the near concentric regime

“…An anaclastic lens has an aspheric surface converting the plane wavefront of a collimated Gaussian input beam to a converging spherical wavefront. A design of cavity mirrors incorporating such an aspheric surface as the input surface of the cavity mirror was proposed in [14], but has in fact been known for a very long time [21,22].…”

“…The design combining cavity mirror and mode-matching lens not only eliminates the aberrations of the coupling optics, but also significantly simplifies alignment, which is a major advantage for the technically challenging concentric configuration. With expressions in [14] for the field quantization, we can associate an effective mode volume for this (standing wave) cavity of…”