Figure 2
APS/Antoine Browaeys

Figure 2: In the experiment of Maxwell et al., the interface consists of an atomic cloud of rubidium atoms, whose states have a ladder configuration (shown on the right). The combination of a weak signal laser and control laser excites one atom (shown in red) into a Rydberg state r, while the other atoms remain in the ground state due to Rydberg blockade (see text). The researchers can couple this collective polariton state to another Rydberg state r using microwaves (MW).