Paper on Imaging and Localizing Individual Atoms Interfaced with a Nanophotonic Waveguide published

Y. Meng, C. Liedl, S. Pucher, A. Rauschenbeutel, and P. Schneeweiss

Single particle-resolved fluorescence imaging is an enabling technology in cold-atom physics. However, so far, this technique has not been available for nanophotonic atom-light interfaces. Here, we image single atoms that are trapped and optically interfaced using an optical nanofiber. Near-resonant light is scattered off the atoms and imaged while counteracting heating mechanisms via degenerate Raman cooling. We detect trapped atoms within 150 ms and record image sequences of given atoms. Building on our technique, we perform two experiments which are conditioned on the number and position of the nanofiber-trapped atoms. We measure the transmission of nanofiber-guided resonant light and verify its exponential scaling in the few-atom limit, in accordance with Beer-Lambert’s law. Moreover, depending on the interatomic distance, we observe interference of the fields that two simultaneously trapped atoms emit into the nanofiber. The demonstrated technique enables postselection and possible feedback schemes and thereby opens the road toward a new generation of experiments in quantum nanophotonics.

Individual atoms (yellow) in the vicinity of a nano glass fiber are photographed with a sensitive camera. A laser beam is used to illuminate the atoms.

Paper on Correlating photons using weakly atoms published

Adarsh S. Prasad, Jakob Hinney, Sahand Mahmoodian, Klemens Hammerer, Samuel Rind, Philipp Schneeweiss, Anders S. Sørensen, Jürgen Volz & Arno Rauschenbeutel

Photons in a nonlinear medium can repel or attract each other, resulting in strongly correlated quantum many-body states1,2. Typically, such correlated states of light arise from the extreme nonlinearity granted by quantum emitters that are strongly coupled to a photonic mode2,3. However, unavoidable dissipation (such as photon loss) blurs nonlinear quantum effects when such approaches are used. Here, we generate strongly correlated photon states using only weak coupling and taking advantage of dissipation. An ensemble of non-interacting waveguide-coupled atoms induces correlations between simultaneously arriving photons through collectively enhanced nonlinear interactions. These correlated photons experience less dissipation than the uncorrelated ones. Depending on the number of atoms, we experimentally observe strong photon bunching or antibunching of the transmitted light. This realization of a collectively enhanced nonlinearity may turn out to be transformational for quantum information science and opens new avenues for generating non-classical light, covering frequencies from the microwave to the X-ray regime.

Paper and Open Data on the Lifetime Measurement of the Cesium 5²D₅⸝₂ State published

We measure the lifetime of the cesium 5²D₅⸝₂ state using a time-resolved single-photon-counting method. We excite atoms in a hot vapor cell via an electric quadrupole transition at a wavelength of 685 nm and record the fluorescence of a cascade decay at a wavelength of 852 nm. We extract a lifetime of 1353(5) ns for the 5²D₅⸝₂ state, in agreement with a recent theoretical prediction. In particular, the observed lifetime is consistent with the literature values of the polarizabilities of the cesium 6P states. Our measurement contributes to resolving a long-standing disagreement between a number of experimental and theoretical results.

In order to improve the traceability of the presented measurements and analysis, the raw experimental data used in this paper has been made available in an open-access repository. Examples of source codes used for the analysis of the data are provided as well.

Paper on 3-photon correlations mediated by a Rydberg superatom

Nontrivial three-photon correlations can be imprinted onto initially uncorrelated photons through an interaction with a single Rydberg superatom, something the SDU group has recently observed experimentally:

By exploiting the Rydberg blockade mechanism, they turn a cold atomic cloud into a single effective emitter with collectively enhanced coupling to a focused photonic mode which gives rise to clear signatures in the connected part of the three-body correlation function of the outgoing photons. The results are in good agreement with a quantitative model for a single, strongly coupled Rydberg superatom. Furthermore, they developed an idealized but exactly solvable model of a single two-level system coupled to a photonic mode, which allows for an interpretation of the experimental observations in terms of bound states and scattering states.