Multiaxis Inertial Sensing with Long-Time Point Source Atom Interferometry

Abstract

We show that light-pulse atom interferometry with atomic point sources and spatially resolved detection enables multi-axis (two rotation, one acceleration) precision inertial sensing at long interrogation times. Using this method, we demonstrate a light-pulse atom interferometer for 87 Rb with 1.4 cm peak wavepacket separation and a duration of 2 T = 2.3 s. The inferred acceleration sensitivity of each shot is 6.7 × 10 −12 g, which improves on previous limits by more than two orders of magnitude. We also measure the Earth's rotation rate with a precision of 200 nrad/s.PACS numbers: 03.75. Dg, 37.25.+k, 06.30.Gv Light-pulse atom interferometry enables precision tests of gravity [1][2][3] and electrodynamics [4] as well as practical applications in inertial navigation, geodesy, and timekeeping. Phase shifts for light-pulse atom interferometers demonstrate sensitivity to the initial velocity distribution of the atom source, often resulting in inhomogeneous dephasing that washes out fringe contrast [5]. In this Letter, we show that use of spatially resolved imaging in combination with an initially spatially localized atomic source allows direct characterization of these phase shifts. We refer to this technique as point source interferometry (PSI).The contrast loss associated with such inhomogeneous dephasing is not fundamental, but is a consequence of atom detection protocols that average over velocitydependent phase shifts. With PSI we establish a correlation between velocity and position and use spatiallyresolved detection to form an image of the ensemble that reveals its velocity-dependent phase structure. A simple way to realize this correlation is through ballistic expansion of the ensemble. In the limit that the ensemble size at detection is much larger than its initial size, each atom's position is approximately proportional to its initial velocity. Consequently, any initial velocitydependent phase shift results in a spatial variation of the interferometer phase, yielding a position-dependent population difference between the two output ports of the interferometer.An important example of velocity sensitivity is due to rotation of the interferometer laser beams [3,6]. Rotation at a rate Ω leads to a phase shift (Table I, term 2) that depends on (v x , v y ), the initial transverse velocity of the atom. In a rotating frame, this effect may be interpreted as a Coriolis acceleration. PSI also allows observation of longitudinal velocity-dependent phase shifts in asymmetric atom interferometers [7] (e.g., Table I, term 3).To demonstrate PSI, we induce a velocity-dependent phase shift in a 87 Rb Raman light-pulse atom interferometer. We launch cold atoms from the bottom of a 10-meter tall vacuum enclosure (Fig. 1a) and apply a threepulse accelerometer sequence (π/2−π−π/2) [8]. The first pulse serves as an atom beamsplitter, coherently driving the atoms into a superposition of states |F = 1; p and |F = 2; p + k eff with momentum difference k eff = 2 k. Over the subsequent T = 1.15 s interrogation interval, the two...

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