Concept study and preliminary design of a cold atom interferometer for space gravity gradiometry

TL;DR

The paper analyzes a space-based gravity gradiometer based on cold-atom interferometry to map Earth's gravity with improved white-noise performance across the measurement bandwidth. It presents a detailed instrument concept, including source preparation, interferometer phase control, a Monte Carlo model of the interferometer, and a full engineering design (vacuum, lasers, mirrors, magnetic shielding, and payload). A closed-loop performance analysis shows that a three-axis, nadir-pointing CAI gradiometer could outperform GOCE in gravity-field recovery, achieving on the order of $5~\mathrm{mE}/\sqrt{\mathrm{Hz}}$ sensitivity and substantial improvements for coefficients with degree higher than ~50 over an 8-month mission. The work also identifies key technical challenges and a path toward prototyping and validation, emphasizing rotation compensation, optical wavefront control, ultracold atomic sources, and power/size optimization for a future gravity mission.

Abstract

We study a space-based gravity gradiometer based on cold atom interferometry and its potential for the Earth's gravitational field mapping. The instrument architecture has been proposed in [Carraz et al., Microgravity Science and Technology 26, 139 (2014)] and enables high-sensitivity measurements of gravity gradients by using atom interferometers in a differential accelerometer configuration. We present the design of the instrument including its subsystems and analyze the mission scenario, for which we derive the expected instrument performances, the requirements on the sensor and its key subsystems, and the expected impact on the recovery of the Earth gravity field.

Figures (19)

• Figure 1: (a) Scheme of the gravity gradiometer, based on differential accelerometry with two separated atom interferometers. (b) An initial BEC source of $10^6$ atoms is magnetically evaporated, displaced and collimated in $1.1$ s. (c) Horizontal transport step to the interferometry chamber (12 cm in 100 ms). (d) The BEC is split in two by the combination of a double Raman diffraction and a twin-lattice technique feeding both interferometers with ensembles at a horizontal velocity of 4 recoils.
• Figure 2: Tilted mirror configuration.
• Figure 3: Double diffraction interferometer scheme using three Raman pulses. Note that we do not display the $\vert\pm 2\rangle$ states as they are pushed away together with the $\vert 0\rangle$ wave-packets.
• Figure 4: Contrast (a) and number of detected atoms (b) as a function of the Rabi pulsation $\Omega_{\mathrm{eff}}$ for different atom temperatures.
• Figure 5: Effect of the Raman lasers waist on the phase shifts at the output of the interferometer at 0.25 m $y$-position (open circles) (resp. at -0.25 m $y$-position (open squares)), and on the differential phase shift between the two interferometers (full triangles). All the Raman laser beams have the same size, at the same $y$-position.