Quantum nonlinear optical devices based on Rydberg technologies

The gap: from strong photon-photon interaction to high-efficiency devices

Remarkable advances have been made towards quantum nonlinearity (strongly-interacting photons) by placing an atom in an optical resonator or coupling to Rydberg states in disordered ensembles (more details).  However, technical and fundamental photon loss hinder many applications and remain the roadblock between a successful lab demonstration and a functional quantum optical device. A high-finesse cavity suffers from losses due to narrow bandwidth, imperfect mode-matching, mirror absorption and scattering, etc. The Rydberg blockade approach is accompanied with intrinsic dissipation, because within the blockade radius, the photon is coupled to an absorptive medium. A nonlinear phase gate based on this approach would have the loss inversely proportional to the optical depth per blockade radius ODB. On the other hand, density-dependent inhomogeneous broadening, due to Rydberg-ground state atom collisions, sets a fundamental limit to ODB, which already plays a detrimental role in the state-of-the-art Rydberg quantum optics experiments. Thus, for high efficiency, high fidelity single-photon-level nonlinear devices, a different scheme or even a new atom-photon interface is desired.