Research

In electronically high-lying Rydberg states, atoms have long life time (tens to hundreds of microseconds) and strong two-body interactions. For example, the van der Waals interaction between Rydberg atoms can be 10 MHz or even larger at 5 micron distances. Such interaction can be much stronger than the laser Rabi frequency, leading to the dipole blockade, i.e. a single Rydberg excitation prevents further Rydberg excitation. The blockade effect finds quantum computation applications (e.g. building entangling gates).

In many-body settings (optical lattices or arrays), the strong interaction allow us to explore various spin models with Rydberg atoms. By modulating Rydberg atom interactions, we have shown that a number of non-conventional models (e.g. non-convex interactions) can be realized. Through Rydberg dressing, we can map the Rydberg atom interaction to the ground state, to probe physics that is driven by two-body interactions and spatial coherence (such as superfluid and supersolid).

The Rydberg atom interaction can be mapped to photon fields through, for example, electromagnetically induced transparency. This turns the free bosons into strongly interacting particles. This mechanism means that Rydberg gases serve a novel quantum interface between photons. By tuning the light-atom coupling and Rydberg states, we can achieve strong interaction between single photons. This allows us to build quantum optical devices that work at the single photon level, including single photon transistor, single photon switch, and single photon sources.

The valance electron of singly charged ions (such as Ca+, Sr+) can be laser excited to Rydberg states. In Rydberg states, the ions are still singly charged and hence can be trapped in the Paul or Penning trap. Compared to ions in ground states, Rydberg ions have long-range interaction due to the large dipole moment. Moreover, the Rydberg electron is affected by the trapping field (electric or RF fields), such that the trapping potential is modified by the Rydberg excitation. The latter can affect the equilibrium properties of the ion crystal, allow to build multiparticle entanglement, and speed up quantum gate operations. Using the Rydberg ion long-range interactions, we can not only achieve quantum entangling, but also engineer the spin-photon coupling to explore novel dynamics (such as creating conical intersections and multi-body long-range interactions).