We conduct atom interferometry on condensates of two isotopes of Rubidium simultaneously. Such a technique has been proposed to experimentally measure the validity of the Weak Equivalence Principle in general relativity, i.e. test whether inertial and gravitational mass the same thing.
We see a relative phase shift between the two interferometers, due to both their different magnetic field sensitivities, and the different scattering properties of each isotope.
(a) By plotting the fraction of each isotope in the output momentum state 1 as an ellipse, the relative interferometric phase shift between the isotopes is measured without common-mode vibrational noise. (b) Looking at the interferometric phase accumulated in a non-interacting 85Rb interferometer while varying the number of co-incident 87Rb atoms can allow a measurement of the inter-isotope scattering length.
This paper presents the first realisation of a simultaneous 87Rb -85Rb Mach-Zehnder atom interferometer with Bose-condensed atoms. A number of ambitious proposals for precise terrestrial and space based tests of the Weak Equivalence Principle rely on such a system. This implementation utilises hybrid magnetic-optical trapping to produce spatially overlapped condensates with a duty cycle of 20s. A horizontal optical waveguide with co-linear Bragg beamsplitters and mirrors is used to simultaneously address both isotopes in the interferometer. We observe a non-linear phase shift on a non-interacting 85Rb interferometer as a function of interferometer time, T, which we show arises from inter-isotope scattering with the co-incident 87Rb interferometer. A discussion of implications for future experiments is given.
To be publish in New Journal of Physics, July 2014.arXiv Preprint