The ICE (Interférométrie atomique à sources Cohérentes pour l'Espace) experiment is a compact and transportable atom interferometer designed to test the weak equivalence principle (also known as the universality of free fall) using cold atomic ensembles of potassium and rubidium while in the microgravity environment generated by parabolic flight.
The experiment is a collaboration between LP2N in Bordeaux and the LNE-SYRTE laboratory in Paris, and is largely funded by the French national Space agency CNES. It is designed to be operated both on ground and onboard the Novespace "Zero-G" Airbus, which makes parabolic flight campaigns out of Bordeaux airport in France.
ICE - Atom Interferometry for Space Applications
Inertial sensors based on matter-wave interferometry have benefited from the progress in laser-cooling techniques over the past 20 years, and offer performances comparable or better than their classical counterparts. Recent developments in laser technologies has made it possible to develop transportable devices, with applications in geophysics, inertial navigation and tests of fundamental physics.
The experimental apparatus was specifically designed to withstand vibrations and temperature fluctuations onboard the Novespace Zero-G aircraft, and was used to demonstrate the first airborne matter-wave inertial sensor in 2010. More recently, in 2015, the ICE team successfully operated two simultaneous interferometers of rubidium-87 and potassium-39 which enabled the first test of the weak equivalence principle in a free-falling vehicle.
Since 2018, we are able to perform experiments in the laboratory thanks to a unique, purpose made Einstein elevator on which the experimental apparatus is installed. This device allows us to access microgravity for up to 500 ms every 12 s and we were able to produce Bose-Einstein condensates with forty thousand rubidium-87 atoms at a temperature of 35 nK in weightlessness. Ultra-cold atomic samples will help improve the sensitivity of our atom interferometer.
The extreme environment of the 0g-plane in terms of temperature variations, vibration levels and congestion entails to have a very compact and robust experimental setup in addition to be transportable. The apparatus thus consists in eight racks independently removable with a weight between 100 and 180kg each. The laser system is almost entirely fibered (except the combining/splitting of the beams which consists in a compact micro-optics bench in ZERODUR developed by muQuanS and Kylia). Based on the frequency-doubled telecom technology, it is immune to misalignment. Diodes and PPLN temperature is very well controlled thanks to numerous lock-in systems.
The vacuum system is made of Titanium and viewports are sealed with indium which gives 19 optical axis for the laser cooling and trapping beams, the detection, the crossed far off resonance dipole trap and three axis for retro-reflected Raman beams for multi-axis inertial measurements. The complete system with collimators and all the optics and detectors is surrounded by a magnetic shield to strongly reduce the external varying magnetic field in the plane. Inside the shield, the homogeneity of the magnetic field is insured by Helmholtz coils pairs and lock-in electronics with a probe.
The Einstein elevator, also known as zero-g simulator, was designed and built by the French company Symétrie (www.symetrie.fr). It works by moving a platform, on which the experimental apparatus rests, in a way that mimicks the trajectory of an object in free fall, launched vertically, i.e. a parabola. The platform moves vertically between two granite columns (2.7 m tall) thanks to two carriages with air bearings for a frictionless motion. Linear motors mounted on the sides of the columns are responsible for the accelerations of the moving parts necessary to perform parabolic trajectories. The 0-g simulator can provide up to half a second of weightlessness on every trajectory and, thanks to its very high repetition rate (1 parabola every 12s), gives access to a very long accumulated duration of 0-g.
The goal of our set-up is to pave the way for onboard atom interferometry and to deals with vibrations and rotation issues. That’s why we developed hybridization technics with classical sensors such as an accelerometer put on the reference mirror and gyroscopes to know the angle of our measurement axis.