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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - RyD-QMB (Rydberg dressed quantum many-body systems)

Teaser

Summary

\"In context of the project \"\"Rydberg dressed quantum many-body systems\"\" (RyD-QMB) we aim to study synthetic quantum many-body systems with long-ranged interactions. Compared to contact interactions, their long-range counterpart introduces a new length scale to quantum many-body problems which can lead to rich new physics. This includes new forms of matter such as supersolids in two or three dimensions or exotic quantum liquids in one dimension. Furthermore, these interactions can be made internal state dependent, such that magnetic quantum systems can be explored. This, on the one hand, allows us to experimentally explore various models for quantum magnets in a highly controlled laboratory environment, on the other hand, it provides a basis for neutral atom based quantum simulation and quantum information with possibly far reaching implications for future technologies.

In RyD-QMB we induce long-ranged interactions between ultracold neutral atoms by laser coupling to so called Rydberg states. These Rydberg states are weakly bound atomic quantum states, where the weak binding between the nucleus and the outer electron leads to a large polarizability and in turn to extremely strong dipole interactions between these atoms. The advantage of the laser controlled interactions is their intrinsic switchability: When the light is switched off, the interactions are absent. Also, by tailoring the laser parameters, especially the frequency and power, one can generate various different forms of interactions, not only differing in their strength, but also in their shape. The main objectives of RyD-QMB are to demonstrate that: 1) Megahertz scale optical coupling can be achieved and that the Rydberg interactions can be controlled by the parameters of the laser, 2) the interactions lead to coherent many-body physics in the continuum with the aim to realize new states of quantum matter and 3) to use these interactions for the study of quantum magnets in optical lattice systems.\"

Work performed

The experimental study of Rydberg induced long-range interactions among ultracold atoms first requires the construction of a dedicated and optimized experimental platform. This platform is a next generation ultracold quantum gas machine based on potassium atoms, where the choice of potassium offers specific advantages when studying quantum magnets and a greater flexibility due to the availability of both a fermionic and a bosonic isotope. During the first half of the project the focus was fully on the construction of this experimental platform. We planned, constructed and implemented a highly integrated ultra-high vacuum system with many components inside the UHV environment. These components involve a custom high resolution imaging objective, water-cooled coils for magnetic field control, electrodes for electric field control and an ion detector for Rydberg detection by ionization. The integration of components in the vacuum system allows for simplification of the experimental setup and optimizes the costs to construct the apparatus. We also developed a state-of-the-art laser cooling setup for potassium, such that we now routinely generate cold gases in the few Microkelvin range. For Rydberg coupling we designed and implemented a frequency quadrupling laser system to generate high power (Watt-scale) ultraviolet light. Furthermore, a home-developed computer control system to synchronize all components of the room size system has been modernized and adapted to our needs. Optical traps for trapping of the potassium atoms have been tested and we are about to load single atoms into them and to observe their fluorescence individually for detection.

In collaboration with another experimental team at the Max-Planck-Institute of Quantum Optics we performed experiments to better understand off-resonantly (aka Rydberg-dressed) quantum gases. These insights are crucial to understand and push the limits to coherence in Rydberg coupled ensembles, a central goal of this project, such that true quantum effects become experimentally accessible. This experiment revealed the existence of so called Rydberg macrodimers, an exotic form of molecules with huge internuclear distance in the order of Micrometers (i.e. of the size of small bacteria). In a further collaboration with theory colleagues we developed ideas for a new detection scheme which may allow for the measurement of correlations at different times. Such non-equal time correlations are not measurable directly so far.

Final results

With the design and construction of the experimental platform we are pushing quantum gas microscopes beyond the state of the art. In particular, our platform is the first one combining high optical access, also for ultraviolet light required for Rydberg coupling, with electrical field control and high resolution imaging. The core of this platform is in operation and we expect that it will enable a new generation of Rydberg many-body experiments in the quantum regime. Furthermore, our platform allows to combine optical lattices with optical microtrap techniques developed in the last few years. Microtraps allow us to create 2d arrangements of atoms as required for the targeted research on quantum magnets with much higher data rate than the traditional approach, while optical lattices allow to study long-range interacting gases in itinerant regimes.

The development of the ultraviolet Rydberg coupling laser is almost finished and first tests show that we can achieve record high coupling strengths with at the same time narrow line widths. Given the intrinsic coherence time limits common to all Rydberg platform due to the lifetime of Rydberg states, the increase in coupling strength will boost the experimentally realizable coherence times beyond what has been achieved until to day.

Together with the improved understanding of Rydberg interactions developed together with collaborator in the last years, the two major technical developments described above put us in a unique position to explore long-range interacting Rydberg many-body systems in the second half of the project.