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Rydberg atoms present a strong dipole dipole interaction, promising for fast quantum gates [1], even in mesoscopic ensembles of ultra-cold atoms: several exeriments have already paved the way to demonstrate suppressions of excitation (dipolar blockade) and spectral braodenings linked to the band of levels caused by the dipole-dipole interaction between ultra-cold Rydberg atoms.
We have analyzed it with a continuous excitation scheme that combines high densities and high resolution spectroscopy: ultra-cold cesium atoms in a MOT are excited with 2 cw laser, a diode laser to 7s state, and a narrow bandwith and tunable laser to Rydberg states. We apply a constant electric field to change and control the interaction between dipoles. We study the interaction around collisional resonance where interactions are easily tuned with electric field. [2] We observe, on the 41p state, a 20 percent reduction of excitation, which demonstrates the dipole blockade. We study this dipole blockade in function of the density of Rydberg atoms, controled by the intensity of our lasers. In the same time, we measure the free ions, formed by collision between Rydberg atoms, to verify that the diminution of our signal is not due to ions, and test the origin of these ions.
[1] D. Jaksch et al., Phys. Rev. Let. 85 2208 (2000) [2] T. J. Carroll Phys. Rev. Let. 93 153001 (2004) [3] T. Vogt et al., arXiv:physics/0603038 (2006) |
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