We discuss techniques for probing the effects of a constant force acting on cold atoms using two configurations of a grating echo-type atom interferometer. Laser-cooled samples of 85 Rb with temperatures as low as 2.4 µK have been achieved in a new experimental apparatus with a wellcontrolled magnetic environment. We demonstrate interferometer signal lifetimes approaching the transit time limit in this system (∼ 270 ms), which is comparable to the timescale achieved by Raman interferometers. Using these long timescales, we experimentally investigate the influence of a homogeneous magnetic field gradient using two-and three-pulse interferometers, which enable us to sense changes in externally applied magnetic field gradients as small as ∼ 4 × 10 −5 G/cm. We also provide an improved theoretical description of signals generated by both interferometer configurations that accurately models experimental results. With this theory, absolute measurements of B-gradients at the level of 3 × 10 −4 G/cm are achieved. Finally, we contrast the suitability of the two-and three-pulse interferometers for precision measurements of the gravitational acceleration, g.
We have developed a technique for measuring the atomic recoil frequency using a single-state echo-type atom interferometer that manipulates laser-cooled atoms in the ground state. The interferometer relies on momentum-state interference due to two standing-wave pulses that produce density gratings. The interference is modified by applying a third standing-wave pulse during the interferometer pulse sequence. As a result, the grating contrast exhibits periodic revivals at the atomic recoil frequency r as a function of the time at which the third pulse is applied, allowing r to be measured easily and precisely. The contrast is accurately described by a coherence function, which is the Fourier transform of the momentum distribution, produced by the third pulse and by the theory of echo formation. If the third pulse is a traveling wave, loss of grating contrast is observed, an effect also described by a coherence function. The decay of the grating contrast as a function of continuous-wave light intensity is used to infer the cross section for photon absorption.
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