High-resolution hybrid atomic quantum gravimeter with real-time vibration compensation

Over the past decades, gravimeters based on different working principles have been developed, such as superconducting gravimeters, spring gravimeters or interferometric gravimeters. Their ability to measure local changes in gravitational acceleration with a very high level of sensitivity makes these instruments widely used in fundamental physics, inertial navigation and geophysics. Recently, quantum gravimeters based on cold atom interferometry have demonstrated some of the best resolution and stability. The atomic quantum gravimeter (AQG) from iXblue is a drift-free absolute gravimeter with a sensitivity of 750 nm/s^2 at 1 sec and a long-term stability that reaches 10 nm/s^2, currently standing as a top-class industry-standard instrument [1]. However, due to its cyclic operation principle, the sensor is subject to dead times and concentrates on low-frequency variations (DC – 1 Hz). In addition, ground vibrations often overshoot the atom interferometer dynamic range. These issues have been demonstrated to be overcome by combining the quantum gravimeter with a classical accelerometer that senses ground accelerations and decouples the atom interferometer from them, so creating a hybrid quantum-classical sensor [2]. We present the hybridization of an Atomic Quantum Gravimeter with a custom-made optical accelerometer. The accelerometer has been specifically designed to optimally reject ground vibrations in the sensitivity range of the atom interferometer in real time. It consists of a force-feedback interferometric inertial sensor with a bandwidth from 10 s to 100 Hz and sub-picometer resolution. The accelerometer mechanics features fused-silica flexures, allowing to reach a 2.8 Hz natural frequency and a mQ-product of 1100 kg in a compact, 10x10x10 cm3, design. The hybridization of the quantum gravimeter with the optical accelerometer is expected to push down the noise floor of both sensors, ultimately hitting the quantum projection noise of the Absolute Quantum Gravimeter, being 350 nm/s2 at 1 sec. This improvement would therefore open new perspectives for applications of the quantum gravimeter, such as Newtonian-Noise estimation or seismic isolation.[1] Ménoret et al, Gravity measurements below 10-9g with a transportable absolute quantum gravimeter, Scientific Reports 8, 12300 (2018)[2] Merlet et al, Operating an atom interferometer beyond its linear range, Mtrologia 46, 87 (2009)[3] Lautier et al, Hybridizing matter-wave and classical accelerometers, Applied Physics Letters 105, 144102 (2014)