EGAS41 - Swansea University

41 st EGAS CP 60 Gdańsk 2009
Towards a Raman quantum memory with Bose-Einstein
condensates
R. Le Targat ∗ , F. Kaminski, N. Kampel, E.S. Polzik, J.H. Müller
QUANTOP, Niels Bohr Institute, Blegdamsvej 17, 2100 Copenhagen, Denmark
∗ Corresponding author: letargat@nbi.dk
Bose Einstein Condensation allows preparing cold and dense atomic samples, providing
conditions very favorable to strong coupling between light and matter. The high optical
depth and an medium favorable to the decoupling between internal and external variables
gives hope for implementing new quantum memory protocols in the near future [1].
Quantum memories with atomic ensembles are based on a collective atomic spin state
and a light state, both showing a strong component along one direction and weak quantum
fields along the others. The interaction is then engineered such as the quantum
quadratures of light are mapped into long-lived atomic states. The Faraday type memory,
already demonstrated for hot atoms [2], maps one light quadrature directly, while
the second one needs to be transferred by a measurement and a feedback sequence. But
ultracold atoms constitute an environment suitable for a pure Raman interaction scheme,
which allows mapping both quadratures directly.
We are implementing a Raman type protocol, based on the two 87 Rb ground states
(F=1, m f =-1) (F=1, m f =+1), and red-detuned from the D1 line. The elongated shape of
the condensate (Fresnel number close to 1.4), together with a number of atoms close to 10 6 ,
provides an on resonance optical depth of several thousands along the long axis (in trap),
enabling thus a strong coupling regime. We will first report on experiments we performed
([3]) in order to check the effectiveness of the decoupling between variables (superradiance
scattering ([4])) in our condensates. This scattering regime corresponds to the limit where
macroscopic momentum is transferred to a part of the BEC, we investigated it as a harmful
process, competing with a functional memory. We will also present the successful loading
of our BECs in a far red-detuned dipole trap, necessary to create a trapping potential
that is ground state insensitive. We will finally report on preliminary Faraday rotation
measurements with BECs in the dipole trap.
References
[1] L-M. Duan, J.I. Cirac, P. Zoller, E.S. Polzik, Phys. Rev. Lett. 85, 5643 (2000)
[2] B. Julsgaard, J. Sherson, J.I. Cirac, J. Fiurášek, E.S. Polzik, Nature 432, 482-485
(2004)
[3] A. Hilliard, F. Kaminski, R. Le Targat, C. Olausson, E.S. Polzik, J.H. Müller, PRA
78, 051403 (2008)
[4] R.H. Dicke, Phys. Rev. 93, 99 (1954)
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