Abstract
We consider the matterwave interferometric measurement of atomic velocities, which forms a building block for all matterwave inertial measurements. A theoretical analysis, addressing both the laboratory and atomic frames and accounting for residual Doppler sensitivity in the beamsplitter and recombiner pulses, is followed by an experimental demonstration, with measurements of the velocity distribution within a 20 K cloud of rubidium atoms. Our experiments use Raman transitions between the long-lived ground hyperfine states, and allow quadrature measurements that yield the full complex interferometer signal and hence discriminate between positive and negative velocities. The technique is most suitable for measurement of colder samples.
Highlights
For vapour phase atoms to reveal their quantum– mechanical characteristics, they must usually be cooled
Weitz and Hänsch proposed the use of velocity-dependent atom interferometry for frequency-independent laser cooling [3], subsequently demonstrated by Dunning et al [4]; and Weiss et al used the technique for measurement of the photon recoil [5]
The continuous-wave beam from a 780 nm distributed feedback diode laser red-detuned from single-photon resonance by ≈ 2π × 13 GHz is spatially divided by a 310 MHz acousto-optical modulator (AOM), and the rest of the microwave frequency shift is achieved by passing the undeflected beam through a 2.726 GHz electro-optical modulator (EOM)
Summary
For vapour phase atoms to reveal their quantum– mechanical characteristics, they must usually be cooled. The sensitivities of quantum superpositions to accelerations, rotations and gravitational fields and gradients have been widely studied [1, 2], there have been few investigations of the velocimetry process that lies at their hearts. This is perhaps because it cannot be used as a sensor of the apparatus’ velocity, since the atom cloud that forms the test mass begins in the same inertial frame as the apparatus. We observe a residual Doppler sensitivity in our beamsplitter pulses, which limits the resolution of our measurements: a theoretical analysis of this effect forms the Appendix 1
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