Physics

Dr. Weibin Li
University of Nottingham

In this talk, I will first give a brief introduction to properties of Rydberg atoms. Due to their strong interactions, interesting two-body and many-body physics can be studied using cold Rydberg gases. A quick overview on some of the topics will be given. In the rest of the talk, I will focus on the application of Rydberg atoms in quantum optics and quantum information processing, particularly on the realization of single photon switches. Recent experiments have realized an all-optical photon switch and transistor using a cold atomic gas. This approach relies on electromagnetically induced transparency (EIT) in conjunction with the strong interaction among atoms excited to high-lying Rydberg states. The transistor is gated via a so-called Rydberg spinwave, in which the whole ensemble coherently shares a single Rydberg excitation. In its absence the incoming photon passes through the atomic ensemble by virtue of EIT while in its presence the photon is scattered rendering the atomic gas opaque. An important current challenge is to preserve the coherence of the Rydberg spinwave during the operation of the transistor, which would enable for example its coherent optical read-out and its further processing in quantum circuits. With a combined field theoretical and quantum jump approach and by employing a simple model description we investigate systematically and comprehensively how the coherence of the Rydberg spinwave is affected by photon scattering. With large-scale numerical calculations we show how coherence becomes increasingly protected with growing interatomic interaction strength. The theoretical model is experimentally verified recently.