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.

Welcome to Humboldt University, Berlin

The largest part of the research group around Prof. A. Rauschenbeutel, ErBeStA consortium member and coordinator, moved this summer to Humboldt University of Berlin. Still, TU Wien will remain in the ErBeStA consortium as a project partner. The corresponding efforts there will be led by Dr. Sarah Bayer-Skoff. Here are a few photos of the move to Berlin.

Paper on Slow light-enhanced optical imaging

M. Scheucher, K. Kassem, A. Rauschenbeutel, P. Schneeweiss, and J. Volz

Optical fibers play a key role in many different fields of science and technology. For many of these applications it is of outmost importance to precisely know and control their radius. In this manuscript, we demonstrate a novel technique to determine the local radius variation of a 30 micrometer diameter silica fiber with sub-Angström precision over more than half a millimeter in a single shot, by imaging the mode structure of the fiber’s whispering gallery modes (WGMs). We show that in these WGMs the speed of light propagating along the fiber axis is strongly reduced, which enables us to determine the fiber radius with significantly enhanced precision, far beyond the diffraction limit. By exciting several different axial modes at different probing fiber positions, we verify the precision and reproducibility of our method and demonstrate that we can achieve a precision better than 0.3 Angström. The demonstrated method can be generalized to other experimental situations where slow light occurs and, thus, has a large range of potential applications in the realms of precision metrology and optical sensing.

Paper on Quantum Optical Networks via Polariton Exchange Interactions

Mohammadsadegh Khazali, Callum R. Murray, and Thomas Pohl

We examine the dynamics of Rydberg polaritons with dipolar interactions that propagate in multiple spatial modes. The dipolar excitation-exchange between different Rydberg states mediates an effective exchange between polaritons that enables photons to hop across different spatial channels. Remarkably, the efficiency of this photon exchange process can increase with the channel distance and becomes optimal at a finite rail separation. Based on this mechanism, we design a simple photonic network that realises a two photon quantum gate with a robust pi-phase, protected by the symmetries of the underlying photon interaction and the geometry of the network. These capabilities expand the scope of Rydberg-EIT towards multidimensional geometries for nonlinear optical networks and explorations of photonic many-body physics.

Paper on prospects for strongly coupled atom-photon quantum nodes

N. Cooper, C. Briddon, E. Da Ros, V. Naniyil, M. Greenaway, L. Hackermueller

We discuss the trapping of cold atoms within microscopic voids drilled perpendicularly through the axis of an optical waveguide. The dimensions of the voids considered are between 1 and 40 optical wavelengths. By simulating light transmission across the voids, we find that appropriate shaping of the voids can substantially reduce the associated loss of optical power. Our results demonstrate that the formation of an optical cavity around such a void could produce strong coupling between the atoms and the guided light. By bringing multiple atoms into a single void and exploiting collective enhancement, cooperativities ~400 or more should be achievable. The simulations are carried out using a finite difference time domain method. Methods for the production of such a void and the trapping of cold atoms within it are also discussed.

Paper on dynamical creation and detection of dark entangled phases in a chiral atom chain on the arXiv

Giuseppe Buonaiuto, Ryan Jones, Beatriz Olmos, Igor Lesanovsky

Open quantum systems with chiral interactions can be realized by coupling atoms to guided radiation modes in waveguides or optical fibres. In their steady state these systems can feature intricate many-body phases such as entangled dark states, but their detection and characterization remains a challenge. Here we show how such collective phenomena can be uncovered through monitoring the record of photons emitted into the guided modes. This permits the identification of dark entangled states but furthermore offers novel capabilities for probing complex dynamical behavior, such as the coexistence of a dark entangled and a mixed phase. Our results are of direct relevance for current experiments, as they provide a framework for probing, characterizing and classifying dynamical features of chiral light-matter systems.

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.