In the project "Rydberg dressed quantum many-body systems" (RyD-QMB) we studied 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. The interactions can be made state dependent, such that magnetic quantum systems can be explored. This allows us to experimentally explore various models for quantum magnets in a highly controlled laboratory environment and provides a basis for neutral atom based quantum simulation and computation.
We induce long-ranged interactions between 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. By tailoring the laser parameters, one can generate various different forms of interactions, not only differing in their strength, but also in their shape. The 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.
Our atomic species of choice is potassium, for which we were the first to trap individual atoms in optical tweezers and to demonstrate coherent Rydberg coupling of the atoms in the array. The laser light for the coupling is derived from novel UV laser system providing more than 1W output at 286nm with very low line width and stable amplitude. This provides enough intensity to reach the Megahertz scale in the optical coupling as required for Rydberg dressing. We and others discovered a collective decoherence channel for Rydberg dressed atoms. An atom in the Rydberg state can decay to a nearby state of opposite parity, opening a very strong dipolar interaction channel. We used our perfectly defined array to study this important effect in detail, which allowed us to demonstrate that it indeed arises from dipolar interactions. In quantum magnets we observed novel types of interactions with non-monotoneous spatial dependence. This required double dressing of two atomic ground states, which define the quantum magnets up and down state.
With these achievements we successfully reached most goals of RyD-QMB and now have one instance of a Rydberg tweezer platform at hand, which is one of the most promising candidates to quantum computing. Future will show if the technology can be advanced far enough to realize a quantum computer with practical use for industrial applications.
