Project 18: Imaging non-local photon interactions with structured light

Summary

Nonlinear, non-local photon interactions can be realised by strong light-matter coupling in Rydberg
gases under conditions of electromagnetically induced transparency (EIT). In this project we aim to
develop a comprehensive picture describing the light propagation through an ultracold Rydberg-EIT
gas of Rubidium atoms in the weakly and strongly interacting regime. For this purpose we will
investigate the optical response of the medium, related to the photon-photon interaction potential,
by measuring its nonlinear susceptibility.

In a first step, we will use structured probe beam light (Fig. 1) to image finite-range photon
interactions in the weakly interacting regime. Since we expect the spatial structure of the third-order
susceptibility to be in the order of the Rydberg blockade radius (approx. a few μm), we plan to design
an objective with a resolution smaller than this emergent length scale. On the theory side, we will
develop an inversion algorithm to reconstruct the non-local susceptibility from the measured Fourier
space components of the output intensity distribution.

Second, we will investigate how the character of the non-local interactions evolves in the crossover
from the weakly to the strongly interacting regime by successively increasing the atomic density.
Here, higher orders of the nonlinear interactions eventually become important and will ultimately
promote rich many body physics. In this regime we plan to explore highly correlated sates of matter
as for example the crystalline state of light.

Fig. 1: Schematic experimental setup for creating structured probe beam light using a spatial light
modulator (SLM) in order to image photon interactions in the weakly interacting regime.

People

Prof. Dr. Thomas Pohl, Aarhus University

Prof. Dr. Matthias Weidemüller, Physikalisches Institut, Universität Heidelberg