We demonstrate a hybrid accelerometer that benefits from the advantages of both conventional and atomic sensors in terms of bandwidth (DC to 430 Hz) and long term stability. First, the use of a real time correction of the atom interferometer phase by the signal from the classical accelerometer enables to run it at best performance without any isolation platform. Second, a servo-lock of the DC component of the conventional sensor output signal by the atomic one realizes a hybrid sensor. This method paves the way for applications in geophysics and in inertial navigation as it overcomes the main limitation of atomic accelerometers, namely, the dead times between consecutive measurements.
We demonstrate a hybrid accelerometer that benefits from the advantages of both conventional and atomic sensors in terms of bandwidth (DC to 430 Hz) and long term stability. First, the use of a real time correction of the atom interferometer phase by the signal from the classical accelerometer enables to run it at best performance without any isolation platform. Second, a servo-lock of the DC component of the conventional sensor output signal by the atomic one realizes a hybrid sensor. This method paves the way for applications in geophysics and in inertial navigation as it overcomes the main limitation of atomic accelerometers, namely, the dead times between consecutive measurements.
Classical inertial navigation systems integrate inertial measurements from triads of accelerometers and gyroscopes to determine their position, but the computed trajectory is typically limited by the intrinsic time-varying bias of these inertial sensors. In addition, the exploitation of quantum physics led to the development of matter-wave interferometers, sensitive to inertial effects due to the mass of the atoms. While they are free-falling, these atoms constitute a perfect inertial frame of reference and allow for an absolute measurement with outstanding accuracy and stability. Substantial technical developments have allowed bringing quantum gravimeters to the market, enabling static, long-term measurements. Nevertheless, the use of cold-atom sensors for navigation and positioning still requires addressing many scientific and technological challenges to be compatible with onboard applications such as compactness, measurement continuity and operation in the presence of strong vibrations and rotations.The Joint Laboratory iXAtom brings together the expertise of the Laboratoire de Photonique, Numérique et Nanosciences (LP2N) in matter-wave interferometry and the French technology company Exail, specialized in high-performance inertial navigation systems and industrial quantum sensors, with the aim of building a new generation of high-end inertial sensors through the hybridization of classical accelerometers and gyroscopes with quantum sensors based on matter-wave interferometry.After successfully building a multi-axis cold-atom interferometer measuring the three components of the acceleration vector with a static apparatus, this quantum inertial sensor has been fully hybridized with a triad of classical accelerometers, increasing the bandwidth and dynamic range without the usual limitation due to the bias drift of the mechanical accelerometers. Moreover, this hybridization technique features a real-time correction of the laser phase which allows retrieving the acceleration information out of atomic fringes scrambled by parasitic vibrations. As regards the rotations of the instrument throughout an interferometer, their compensation remains the next major issue to tackle for strapdown applications as they induce a drastic reduction of the atomic fringes’ visibility coupled to a scrambling of the interferometric phase shift.This thesis work focuses on the mitigation of the rotation-induced performance deterioration of the hybrid accelerometer. Through a theoretical investigation, a model for both the angular velocity-dependent decay of the fringes contrast and the systematic phase shift arising from the complex trajectory of the atomic cloud in the rotating frame of the interrogation laser is established. A real-time rotation compensation system, employing the measurement of the rotation rate with high-end fiber-optic gyroscopes to drive a piezo-actuated tip-tilt platform, has been implemented to stabilize the orientation of the interrogation laser in the external frame in order to preserve the contrast of the atomic interference pattern and extend the measurement range of the rotating atom interferometer. A rectification of the theoretical model accounting for the rotation of the laser as well as the hybridization with the classical accelerometers enables reconstructing the atomic fringes and retrieving the inertial measurement, paving the way for strapdown onboard hybrid accelerometry.
Matter-wave interferometry has enabled high precision measurements of inertial forces such as gravity and the Coriolis force. This is facilitated by the long-term stability of the physical properties of atoms and lasers. Recent experiments have demonstrated the operation of portable, robust sensors using atom interferometry. This has potential uses in the context of inertial navigation, where conventional devices suffer from long-term drifts due to bias instability. Furthermore, determining position via dead reckoning requires minimisation of dead time between measurements. This thesis presents the development of an atom interferometer for measuring horizontal accelerations. In this configuration, gravity induces motion across the laser wavefront, which constrains the tolerable level of wavefront distortions. Effective control of the experiment allows the interferometer to be operated at a rate of 4 Hz. A cold ensemble of 10^6 atoms in the same internal state is prepared in 150 ms. The interferometer operates using a sequence of three laser pulses separated by T= 25 ms to achieve sensitivity to horizontal accelerations. Combining this with a classical accelerometer provides a method of correcting for vibration-induced noise, as well as determining the interferometer fringe order. After an integration time of 40 s, the sensitivity to horizontal accelerations is better than 3^-6 m s^-2. Effects which limit this sensitivity are discussed.
Robust and accurate acceleration tracking remains a challenge in many fields. For geophysics and economic geology, precise gravity mapping requires onboard sensors combined with accurate positioning and navigation systems. Cold atom–based quantum inertial sensors can potentially provide these high-precision instruments. However, current scalar instruments require precise alignment with vector quantities. Here, we present the first hybrid three-axis accelerometer exploiting the quantum advantage to measure the full acceleration vector by combining three orthogonal atom interferometer measurements with a classical navigation-grade accelerometer triad. Its ultralow bias permits tracking the acceleration vector over long time scales, yielding a 50-fold improvement in stability (6 × 10 −8 g ) over our classical accelerometers. We record the acceleration vector at a high data rate (1 kHz), with absolute magnitude accuracy below 10 μ g , and pointing accuracy of 4 μrad. This paves the way toward future strapdown applications with quantum sensors and highlights their potential as future inertial navigation units.
Inertial sensors relying on atom interferometry offer a breakthrough advance in a variety of applications, such as inertial navigation, gravimetry or ground- and space-based tests of fundamental physics. These instruments require a quiet environment to reach their performance and using them outside the laboratory remains a challenge. Here we report the first operation of an airborne matter-wave accelerometer set up aboard a 0g plane and operating during the standard gravity (1g) and microgravity (0g) phases of the flight. At 1g, the sensor can detect inertial effects more than 300 times weaker than the typical acceleration fluctuations of the aircraft. We describe the improvement of the interferometer sensitivity in 0g, which reaches 2 x 10-4 ms-2 / √Hz with our current setup. We finally discuss the extension of our method to airborne and spaceborne tests of the Universality of free fall with matter waves. Inertial sensors using atom interferometry have applications in geophysics, navigation- and space-based tests of fundamental physics. Here, the first operation of an atom accelerometer during parabolic flights is reported, demonstrating high-resolution measurements at both 1g and 0g.
We study two hybridization algorithms that are used for combining a quantum inertial sensor based on atom interferometry with a classical inertial sensor for onboard acceleration measurements. The first is based on the direct extraction of the interferometer phase and has previously been used in seaborne and airborne gravity-measurement campaigns. The second relies on the combination of three consecutive measurements and was originally developed to increase the measurement range of the quantum sensor beyond its linear regime. After comparing their performances using synthetic data, we implement them on acceleration data collected in a recent airborne campaign and evaluate the bias and scale-factor error of the classical sensor. We, then, extend their scope to the dynamical evaluation of other key measurement parameters (e.g., alignment errors). We demonstrate an improvement in the correlation between the measurements of the two accelerometers, and we observe a significant reduction in the error in the estimation of the bias of the classical sensor.
Atom interferometers are among the most sensitive inertial sensors, yet deployment outside the laboratory is limited by vibration noise, conventionally mitigated by external sensors or bulky isolation. Here we demonstrate a hybrid inertial sensor which fuses an optomechanical resonator and an atom interferometer by exploiting the resonator's test mass as the interferometer's reference mirror. This allows for better correlation than with two separate sensors, whose unknown transfer function is replaced by the static response of one mechanical element. The resonator achieves a displacement sensitivity of 8.6⋅10−15 m/Hz with suppressed 1/f noise and yields a minimum acceleration sensitivity of 1.1⋅10−6 m/s2/Hz over a bandwidth extending from sub-Hertz to 2.5 kHz. Under ambient laboratory conditions the integrated system removes vibration-induced phase ambiguity for accelerations up to 50⋅10−3 m/s2 and reaches the interferometer's technical noise limit, which a commercial force-balance accelerometer does not. Because the resonance-tracking readout is largely independent of the mechanical design, the architecture transfers directly to other precision sensing platforms.