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Dr. Valentina Parigi

Laboratoire Charles Fabry, Institut d'Optique, CNRS, Univ Paris-Sud

Thursday, December 20th, 2012 at 10:30:00 AM  

Conference room Querzoli - LENS - via Nello Carrara 1 - Sesto Fiorentino (Florence)

Published on-line at 03:39:41 PM on Monday, December 3rd, 2012

Measurement of giant dispersive optical non-linearities and non-classical state generation in an ensemble of cold Rydberg atoms

Using Van der Waals interactions in Rydberg ensembles to mediate photon-photon interactions.

We measured strong dispersive optical non-linearities in an ensemble of cold Rydberg atoms placed inside an optical cavity (arXiv:1209.1948). Achieving very large optical non-linear effects, able to create photon-photon interactions, would be an essential step forward for quantum information processing and communications. In particular a dispersive and non-dissipative non-linearity at the single-photon level could enable the implementation of a two-photon phase gate. We are following one of the most promising current approaches which exploits the Van der Waals interactions in Rydberg ensembles to mediate photon-photon interactions.

We observed that the atomic interactions strongly enhance the non-linear response of the cloud, in agreement with a simple model where the optical non-linearities are due to the progressive appearance of a Rydberg blockaded volume within the medium. Though much progress is still needed to reach the regime of large dispersive photon-photon interactions in the optical domain our result is the first measurement of a dispersive non-linear susceptibility of such magnitude in Rydberg gases.

Rydberg media could also be exploited to achieve the deterministic generation of non-classical states of light. The quantum state of a light beam can be stored in an ensemble of cold atoms as a polarisation wave involving two long-lived atomic states. If one of these atomic states is a Rydberg state, this polariton will evolve due to long-range atomic interactions. As a result, a coherent pulse of light stored in the atomic medium should turn into a non-classical polaritonic state which could be retrieved as a pulse of non-classical light. We have theoretically shown that the Rydberg gas should act as "quantum scissors" on the stored quantum state, and the retrieved optical pulse should become a coherent superposition of zero and one photons presenting a non-classical, negative Wigner function (10.1103/PhysRevA.86.021403).

For further informations, please contact Dr. Alessandro Zavatta.