Rydberg EIT Overview

To create an effective strong interaction between probe photon, a ladder-type EIT scheme with single-photon probe light at 780 nm and stronger control light at 480 nm is employed to adress Rydberg states in our ultra-cold atomic cloud of 87Rb atoms.

blockade mechanism

Once excitation to a Rydberg state occurs, strong interaction and non-trivial mixing of other Rydberg states is observed. A strong manifestation of the interaction strength is the Rydberg blockade effect: the pair potential (two excitations) V(r) can be higher than the excitation linewidth even at separations of r > 10 micrometer. As a result, for constant laser frequencies, Rydberg excitations can only occur with a certain mesoscopioc separation.

chain_of_superatoms

Rydberg-EIT and the blockade effect give rise to a collective nonlinearity [1][2]: the probe photon propagates at a reduced group velocity (or is even stored) in the medium as a delocalized spin wave, the excitation is shared by all atoms in the excitation volume and the electrical susceptibility is non-local with a non-zero χ(3) component. Nonlinear transmission of single-mode probe light is the most striking evidence for strong interaction, as can be seen in our transmission spectra at different probe powers: compare transmissions at zero detuning.

nonlinearity scans

Plenty of ideas can be realized in systems of strongly interacting photons. As an example from our research, a single photon transistor can be implemented by making use of the Rydberg excitation blockade between states with different principle quantum numbers.

More information can be found in [3].

References:

[1] J.D. Pritchard, D. Maxwell, A. Gauguet, K.J. Weatherhill, M.P.A. Jones, C.S. Adams, PRL 105, 193603 (2010)
[2] T. Peyronel, O. Firstenberg, Q. Liang, S. Hofferberth, A. Gorshkov, T. Pohl, M. Lukin, V. Vuletic, Nature 488, 57 (2012)
[3] J. D. Pritchard, K. J. Weatherill, C. S. Adams, Annual Review of Cold Atoms and Molecules, 1, 301 (2013) (arXiv:1205.4890)