EGAS41 - Swansea University

41 st EGAS CP 131 Gdańsk 2009
Atom interferometry measurement of the atom–surface
interaction
S. Lepoutre 1 , H. Jelassi 1 , G. Trénec 1 , M. Büchner 1,∗ , J. Vigué 1 , V.P.A. Lonij 2 ,
A.D. Cronin 2
1 LCAR-IRSAMC, Université de Toulouse UPS-CNRS UMR 5589
2 Department of Physics, University of Arizona, Tucson, USA
∗ Corresponding author: matthias.buchner@irsamc.ups-tlse.fr
Atom interferometers are a well established tool to measure the phase shift induced by
weak perturbations on the propagation of atomic de Broglie waves. Our Mach-Zehnder
atom interferometer operates with lithium at thermal energy and Bragg diffraction by
near-resonant laser standing waves is used to split, reflect and recombine the atomic
beams. The distance between the two coherent atomic beams is about 100 µm, sufficient
to apply a perturbation to one beam only and to observe the resulting phase shift and
attenuation of the atomic wave on the interferometer signal. We have thus measured very
accurately the electric polarisabiliy of 7 Li [1] and the index of refraction of rare gases for
lithium matter waves [2].
To measure the van der Waals lithium-surface interaction, we introduce a 100 nm period
nanograting on one atomic beam in our interferometer, thus following an experiment
done by Perreault and Cronin with sodium [3]. The nanograting diffracts the atomic
beam and only the zero-order beam interferes with the reference beam. The interference
signals give access to the zero-order diffraction amplitude. The phase of this amplitude
is solely due to the atom-surface Van der Waals interaction. We have carefully measured
this phase as a function of the atom velocity from 700 to 3300 m/s (see figure 1) and we
have obtained an uncertainty of the order of 3 milliradians, thus reducing the uncertainty
of the previous experiment [3] by a factor 33! The velocity dependence of this phase is
a test of the potential dependence with the atom-surface distance r and, if we assume a
C p /r p potential, our data proves that p = 2.9 ± 0.2, as predicted by theory. Our data
can also be used to set new limits on non-Newtonian gravity in the 1 − 10 nm range. Finally
the phase gives a direct measurement of the lithium SiN x van der Waals coefficient
C 3 = 3.25 ± 0.2 meV/nm 3 in good agreement with theory.
0.25
Induced Phase (Rad)
0.20
0.15
1st order diffraction
second order diffraction
1/r 3 Numerical model fit
1/r 4 Numerical model fit
1/r 2 Numerical model fit
Power law fit
1000
1500 2000
Mean Velocity (m/s)
2500
3000
Figure 1: Measured phase of the diffraction amplitude as a function of atom velocity.
References
[1] A. Miffre A. et al., Eur. Phys. J. D 38, 353-365 (2006)
[2] M. Jacquey et al. Phys. Rev. Lett. 98, 240405 (2007)
[3] J.D. Perreault, A.D. Cronin Phys. Rev. Lett. 95, 133201 (2005)
[4] S. Lepoutre, H. Jelassi H., G. Trénec, M. Büchner, J. Vigué, V. Lonij, A. Cronin,
submitted to Phys. Rev. Lett.
191