Strongly interacting single photons in an ultra-cold Rydberg gas

• Applicant: Professor Dr. Sebastian Hofferberth
• Subject Area: Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2012 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 212806422

Strong photon-photon coupling can in principle be achieved inside extremely nonlinear media. The search for few-photon nonlinearities is a highly active field, including such diverse systems as quantum dots, NV centers in diamond, atomic ensembles, and single atoms in optical resonators. However, no robust and scalable realization of, for example, a single-photon switch has been achieved so far. In this project we will realize a novel method for dramatically enhancing photon-photon interactions by mapping quantum correlations between strongly interacting atoms inside an ultra-cold gas onto single photons. Using electromagnetically induced transparency (EIT) to coherently convert photons into Rydberg atoms, we will exploit the strong atom-atom interaction between highly excited atoms to manipulate light on the single-photon level. This interface between quantum states of light and strongly correlated quantum media opens a completely new research field beyond classical nonlinear optics. In the course of this project we will use this technique to implement fundamental building blocks for photonic quantum information processing, such as a deterministic single-photon source and a quantum phase gate. Furthermore, we will apply our system of interacting photons to the study of strongly correlated many-body systems, realizing a unique approach of simulating complex many-body Hamiltonians with quantum optics tools.

• DFG Programme: Independent Junior Research Groups
• Major Instrumentation: Rydberg-excitation laser operating at 480 nm
• Instrumentation Group: 5700 Festkörper-Laser