Ultracold Rydberg Gases

Ultracold Rydberg Gases

Over the last decades, versatile model systems for experimentally studying strongly-correlated many-body quantum systems and their dynamics have been realized. In ultracold atomic gases, produced via laser cooling and trapping, the Hamiltonian governing the equilibrium state and the evolution can be known precisely, the relevant system parameters can be precisely tuned, and key observables can be directly accessed. However, in most experiments, the crucial atomic interactions which lead to complex behaviour are relatively simple and short ranged (which is an important distinction from e.g. strongly correlated materials).

Highly-excited atoms called ultracold Rydberg atoms, have extreme properties which give rise to completely new physical effects. In particular, because of the weak binding of the outer electron to the nucleus, Rydberg atoms react very sensitively to external fields, and experience extremely strong interactions amongst one another, even over macroscopic length scales. In an ensemble of atoms, these interactions prevent more than one Rydberg atom to be excited at a time (Rydberg blockade), leading to the emergence of strong spatial and temporal quantum correlations. By interfacing laser light with Rydberg atoms, we can engineer synthetic systems for studying how many-body quantum systems evolving under the influence of long-range and widely tunable interactions.

Group members Tobias and Sayali standing beside the ultracold Rydberg apparatus in Strasbourg

In the Exotic Quantum Matter Laboratory, we have built a new experimental apparatus that combines ultracold potassium atoms with strong coherent laser coupling to Rydberg states making it possible to introduce and control long-range interactions. Our setup includes an ultrahigh vacuum system with outstanding optical access, an in-vacuum electrode assembly for controlling electric fields and an objective lens for high resolution fluorescence imaging. It also includes a high-flux source of ultracold potassium atoms (2D magneto optical trap) and a versatile tapered amplifier based laser system for laser cooling on the D1 and D2 transitions. With this system we have separately produced samples of laser cooled potassium-39 (a boson) and small samples of potassium-40 (a fermion) in a magneto optical trap. Using gray optical molasses cooling we have cooled the atoms to a temperature of approximately 15 μK and loaded the atoms into a crossed-beam optical dipole trap. Another key aspect of our experiment is a high power laser platform for exciting Rydberg states of potassium. This consists of a single frequency dye laser producing 575 nm light, which is then was frequency doubled to generate 288 nm UV light for single-photon excitation of potassium Rydberg states. In addition, we have a new high power semiconductor laser system for generating 457 nm, which makes it possible to simultaneously perform single-photon and two-photon Rydberg dressing.

More details about our experimental approach can be found in the following papers

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