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Project Area B:
Rydberg Aggregates

The dynamics of highly excited Rydberg systems has now been explored far beyond atomic physics in different contexts from quantum optics (see research area 3.1) over interfaces (3.3) to many-body physics in condensed matter (3.4). Yet another promising context is the field of quantum chemistry. Indeed, a spectacular prediction (1) of modern Rydberg physics, which was proven experimentally (2), is the existence of ultra-long-range molecules formed by a Rydberg system and another one in the ground state, in the simplest case, e.g., two Rubidium atoms. What makes chemical binding interesting for Rydberg physics is the joint and coherent motion of nuclei and electrons. Rather than fighting nuclear motion as a kind of thermal noise and source of decoherence in an otherwise frozen ultracold Rydberg gas, one can try to use electronic motion to initiate directed nuclear motion. This in turn can trigger further electronic motion to achieve coherent electronic exciton transport over many micrometer distances – this is the idea of Rydberg aggregates built up by identical excited units linked by resonant dipole-dipole forces. Introduced with a chain of Rydberg atoms in a quantum version of Newton’s cradle (3), it has been shown now that ensembles of atoms with a single excitation, so called “superatoms” (4) can replace a single Rydberg atom in the aggregate which will eventually facilitate the experimental approach to Rydberg aggregates greatly. A second theme of Rydberg aggregates is provided by creating nanostructured arrays, e.g, with nanotubes (5), where each tube can carry a Rydberg excitation. Such arrays could fulfill similar tasks as optical lattices in terms of processing, storing and switching electronic excitation, here now with a Rydberg electron, yet under physical conditions that are much easier to handle. Finally, one can create yet another type of spatially correlated aggregates namely Rydberg liquids, by exploiting the manifold structures of the molecular interaction potentials, either in the incoherent regime in thermal gases (6) (7) or coherently in an ultracold gas (8) (9). A major task will be to resolve the liquid type spatial correlations within the gaseous background.

Research on Rydberg aggregates will explore largely uncharted territory, and where a few foundations have already been laid as described above, work in the SPP shall advance our knowledge well beyond the present state. It is our goal to establish different types of aggregates and to study their non-equilibrium properties and the corresponding spatial correlations which resemble similarities to solid, liquid and gaseous situations.

1. C. H. Greene, A. S. Dickinson, and H. R. Sadeghpour. Creation of Polar and Nonpolar Ultra-Long-Range Rydberg Molecules. Phys. Rev. Lett. 85, 2458 (2000).

2. V. Bendkowsky, B. Butscher, J. Nipper, J. P. Shaffer, R. Löw, T. Pfau. Observation of ultralong-range Rydberg molecules. Nature 458, 1005 (2009).

3. S. Wüster, C. Ates, A. Eisfeld, J. M. Rost. Newton's Cradle and Entanglement Transport in a Flexible Rydberg Chain. Phys. Rev. Lett. 105, 0534004 (2010).

4. T. M. Weber, M. Höning, T. Niederprüm, T. Manthey, O. Thomas, V. Guarrera, M. Fleischhauer, G. Barontini, H. Ott. Creation, excitation and ionization of a mesoscopic superatom. arXiv: 1407.3611 (2014).

5. J.-C. Charlier, X. Blase, S. Roche. Rev. Mod. Phys. 79, 677 (2007).

6. I. Lesanovsky, J. P. Garrahan. Out-of-equilibrium structures in strongly interacting Rydberg gases with dissipation. Phys. Rev. A 90, 011603 (R) (2014).

7. A. Urvoy, F. Ripka, I. Lesanovsky, D. Booth, J. P. Shaffer, T. Pfau, R. Löw. Strongly correlated growth of Rydberg aggregates in a vapour cell. arXiv:1408.0039 (2014).

8. H. Schempp, G. Günter, M. Robert-de Saint-Vincent, C. S. Hofmann, D. Breyel, A. Komnik, D. W. Schönleber, M. Gärttner, J. Evers, S. Whitlock, M. Weidemüller. Full counting statistics of laser excited Rydberg aggregates in a one-dimensional geometry. Phys. Rev. Lett. 112, 013002 (2014).

9. N. Malossi, M. Valado, S. Scotto, P. Huillery, P. Pillet, D. Ciampini, E. Arimondo, O. Morsch. Full counting statistics and phase diagram of a dissipative Rydberg gas. Rev. Lett. 113, 023006 (2014).

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