Long-range interacting quantum gases in spatially separated traps
Final Report Abstract
The DFG project has explored the physics of quantum many-body systems enhanced with strong long-range interactions by laser coupling to highly excited Rydberg states. In the first phase of this project we built a new state-of-the-art experimental apparatus which combines optically trapped gases of ultracold potassium atoms with laser dressing of Rydberg states. The key capabilities include: outstanding optical access for optical traps and Rydberg excitation lasers, relatively short experimental cycle times ∼ 2 seconds, laser system for bright and grey molasses cooling of the atoms, integrated electrode assembly and micro-channel plate detectors for Rydberg state detection and a versatile laser system for Rydberg dressing using either one-photon or two-photon excitation schemes. The high degree of flexibility concerning the Rydberg states used (and their interaction properties), the trap geometries and the relevant laser couplings makes this a unique platform for addressing fundamental questions concerning the phase structure and dynamics of long-range interacting quantum matter in new regimes. Parallel to the experimental build up we theoretically studied Rydberg dressing with the goal to find the optimal parameter regimes, including experimentally realistic effects, such as the multilevel structure of the atoms and dissipation due to shortlived atomic states. Along the way we discovered some intriguing physics related to how Rydberg dressing can be used to influence quantum dynamics in non-trivial ways, for example, in order to control the transport of spin or energy of individual excitations through the introduction of correlated disorder or tailored dissipative environments. We also theoretically studied the phase structure of the dipolar Fermi-Hubbard ladder by Rydberg dressing, finding that it is even richer than originally anticipated, exhibiting a number of exotic magnetic and superfluid phases. In our experiments we focused on two-photon laser excitation of Rydberg states in an optically trapped atomic gas using a combination of 767 nm and 457 nm laser fields. We achieved strong atom-light coupling strengths combined with dressed-state lifetimes exceeding typical motional timescales. We also devised a novel way to investigate the properties of Rydberg-dressed atomic gases via their decay to non-coupled states. We then embarked on a major experimental study of the phase structure of a prototypical driven-dissipative quantum spin system. We showed that the slow population loss inherent to our system provides a convenient observable for the many-body state of the non-equilibrium system, which we could measure over several orders of magnitude. Unexpectedly, we discovered that the rate of population loss exhibits powerlaw scaling with the driving strength with exponents that depend on the range of Rabi frequencies and detunings of the dressing laser. We use this to uncover the full non-equilibrium phase structure of the many-body system, which includes features which can be attributed to the equilibrium quantum Ising model, but also but also genuinely new non-equilibrium features, e.g. the collectively enhanced crossover from a dissipation-dominated to a critical regime and an instability which drives the system to strongly-correlated states for positive detunings. More generally, we expect that the observed scaling laws can provide a much needed tool for classifying quantum systems out of equilibrium and as a benchmark for state-of-the-art many-body theory. In the future it will be interesting to explore the transition from the driven-dissipative regime to the fully-isolated regime and to search for general laws governing nonequilibrium quantum dynamics. With this in mind, we recently demonstrated coherent dynamics of an isolated quantum spin system following a quantum quench, formed using two different Rydberg states with different angular momenta coupled by a microwave field. In this system the competition between coherent microwave driving and long-range dipolar interactions occurs on timescales much faster than typical decoherence rates, making it an ideal system for exploring the emergence of correlations and entanglement in complex quantum systems.
Publications
- Collective Excitation of Rydberg-Atom Ensembles beyond the Superatom Model, Phys. Rev. Lett. 113, 233002 (2014)
Martin Gärttner, Shannon Whitlock, David W. Schönleber, Jörg Evers
(See online at https://doi.org/10.1103/PhysRevLett.113.233002) - Correlated Exciton Transport in Rydberg-Dressed-Atom Spin Chains, Phys. Rev. Lett. 115, 093002 (2015)
H. Schempp, G. Günter, S. Wüster, M. Weidemüller, S. Whitlock
(See online at https://doi.org/10.1103/PhysRevLett.115.093002) - Quantum Simulation of Energy Transport with Embedded Rydberg Aggregates, Phys. Rev. Lett. 114, 123005 (2015)
D. W. Schönleber, A. Eisfeld, M. Genkin, S. Whitlock, S .Wüster
(See online at https://doi.org/10.1103/PhysRevLett.114.123005) - Density matrix reconstruction of three-level atoms via Rydberg electromagnetically induced transparency, Journal of Physics B: Atomic, Molecular and Optical Physics49, 164002 (2016)
V Gavryusev, A Signoles, M Ferreira-Cao, G Zürn, C S Hofmann, G Günter, H Schempp, M Robertde-Saint-Vincent, S Whitlock, M Weidemüller
(See online at https://doi.org/10.1088/0953-4075/49/16/164002) - Two-body interactions and decay of three-level Rydberg-dressed atoms, Journal of Physics B: Atomic, Molecular and Optical Physics 49, 03LT02 (2016)
S Helmrich, A Arias, N Pehoviak, S Whitlock
(See online at https://doi.org/10.1088/0953-4075/49/3/03LT02) - A versatile, high-power 460nm laser system for Rydberg excitation of ultracold potassium, Optics Express, 25, 14829-14839 (2017)
Alda Arias, Stephan Helmrich, Christoph Schweiger, Lynton Ardizzone, Graham Lochead, Shannon Whitlock
(See online at https://doi.org/10.1364/OE.25.014829) - Simulating quantum spin models using Rydberg-excited atomic ensembles in magnetic microtrap arrays, Journal of Physics B: Atomic, Molecular and Optical Physics 50, 074001 (2017)
S. Whitlock, Alexander A. Glaetzle, Peter Hannaford
(See online at https://doi.org/10.1088/1361-6455/aa6149) - Relaxation of an isolated dipolar-interacting Rydberg quantum spin system, Phys. Rev. Lett. 120, 063601 (2018)
A. Pineiro Orioli, A. Signoles, H. Wildhagen, G. Günter, J. Berges, S. Whitlock, M. Weidemüller
(See online at https://doi.org/10.1103/PhysRevLett.120.063601)
