Cold Atomic Ensembles

The cold atoms lab uses cold clouds of Rubidium-87 trapped atoms to develop efficient resources for quantum networks. Two experiments are currently running:

In the Rydberg experiment, a crossed dipole trap is used to confine a small atomic ensemble (<15 μm), where two-photon excitation (795 nm and 474 nm) address Rydberg states. The Rydberg blockade effect, arising from dipole-dipole interactions between Rydberg states, prevents multiple excitations within the cloud, resulting in the creation of a single collective Rydberg polariton. This highly nonlinear system, often referred to as a ‘superatom,’ behaves like a single-atom system while leveraging the collective properties of the ensemble. We use this efficient system to generate single photons and light-matter entanglement in a quasi-deterministic manner. Additionally, we exploit its nonlinearity to perform photon-photon quantum gates and generate cluster states. Currently, the system is being upgraded to couple it with a medium-finesse cavity.

The DLCZ experiment utilizes a large cloud of cold atoms held in a magneto-optical trap. Through off-resonant Raman scattering, we herald collective spin excitations that can later be read out as single photons, establishing a foundational element for quantum repeater schemes. A quantum frequency conversion setup shifts the 780 nm photons to the telecom band, enabling integration of this cold-atom system with the group’s other solid-state platforms. This system facilitates experiments on heralded single-photon generation, Bell-state creation, and entanglement swapping.