The accelerometer plays a crucial role in inertial navigation. The performance of conventional accelerometers such as lasers is usually limited by the sensing elements and shot noise limitation (SNL). Here, we propose an advanced development of an accelerometer based on atom–light quantum correlation, which is composed of a cold atomic ensemble, light beams, and an atomic vapor cell. The cold atomic ensemble, prepared in a magneto-optical trap and free-falling in a vacuum chamber, interacts with light beams to generate atom–light quantum correlation. The atomic vapor cell is used as both a memory element storing the correlated photons emitted from cold atoms and a bandwidth controller through the control of free evolution time. Instead of using a conventional sensing element, the proposed accelerometer employs interference between quantum-correlated atoms and light to measure acceleration. Sensitivity below SNL can be achieved due to atom–light quantum correlation, even in the presence of optical loss and atomic decoherence. Sensitivity can be achieved at the ng / Hz level, based on evaluation via practical experimental conditions. The present design has a number of significant advantages over conventional accelerometers such as SNL-broken sensitivity, broad bandwidth from a few hundred Hz to near MHz, and avoidance of the technical restrictions of conventional sensing elements.
The accelerometer plays a crucial role in inertial navigation. The performance of conventional accelerometers such as lasers is usually limited by the sensing elements and shot noise limitation (SNL). Here, we propose an advanced development of an accelerometer based on atom–light quantum correlation, which is composed of a cold atomic ensemble, light beams, and an atomic vapor cell. The cold atomic ensemble, prepared in a magneto-optical trap and free-falling in a vacuum chamber, interacts with light beams to generate atom–light quantum correlation. The atomic vapor cell is used as both a memory element storing the correlated photons emitted from cold atoms and a bandwidth controller through the control of free evolution time. Instead of using a conventional sensing element, the proposed accelerometer employs interference between quantum-correlated atoms and light to measure acceleration. Sensitivity below SNL can be achieved due to atom–light quantum correlation, even in the presence of optical loss and atomic decoherence. Sensitivity can be achieved at the ng / Hz level, based on evaluation via practical experimental conditions. The present design has a number of significant advantages over conventional accelerometers such as SNL-broken sensitivity, broad bandwidth from a few hundred Hz to near MHz, and avoidance of the technical restrictions of conventional sensing elements.
Quantum sensing using atom interferometry possesses immense potential for application in gravimetry, inertial navigation and for gravitational wave detection, apart from carrying out tests of fundamental physics. Atom interferometry can be used to perform absolute inertial measurements with unprecedented long term stability, unlike classical sensors which are prone to drift and incur calibration errors. However, atom interferometers seldom achieve their fundamental sensitivity due to the coupling of ambient vibrations. It is the dominant noise source that not only impairs performance but also affects its operability. Ideal compensation of the effects due to vibration noise using a versatile accelerometer, while concurrently enabling miniaturized atom interferometer setups has not been pioneered. Such a compact hybrid quantum sensor will enable reliable operation with an enhanced performance in field applications, paving the way for robust atom interferometry beyond laboratory conditions. A novel optomechanical resonator has been designed, developed and successfully hybridized with an atom interferometer to suppress the effects of vibration noise, and the results are presented in this thesis. The optomechanical resonator’s inertial test mass is simultaneously used to create a continuous intracavity optical lattice to sense its displacement, and a pulsed optical lattice to manipulate the atoms. For the first time, a broadband accelerometer is seamlessly hybridized with an atom interferometer via mechanical resonator mediated coupling of the optical lattices to measure acceleration. This enables elimination of vibration induced measurement ambiguity in our atom interferometer with a well defined mechanical transfer function. Vibration noise correlation is demonstrated up to our prototype atom interferometer’s most sensitive operating mode of T = 6 ms using double Bragg diffraction, ultimately limited by its technical noise. The optomechanical resonator measures acceleration with a sensitivity down to 1.1×10−6 ms−2/ √Hz corresponding to a displacement sensitivity of 8.6 × 10−15 m/ √Hz. Substantial 1/f noise suppression due to the developed optical readout scheme enables a measurement bandwidth spanning from sub-hertz frequencies up to several kilohertz. Multiple versions of the optomechanical resonator with different characteristics were developed and hybridized with our atom interferometer. This paves the way for developing tailored optomechanical resonators for specific inertial sensing applications.
Inertial navigation systems are vital for modern society, be it on airplanes or in the context of autonomous mobility. On the other hand atom interferometers are exquisite measurement devices for inertia in fundamental physics and field applications, but are mostly limited to measuring one inertial observable. By utilizing time averaged optical potentials, the ultra-cold atomic ensemble input to the interferometer can be prepared in nearly arbitrary fashion. This results in a boost of preparation speed and number of atoms in the interferometer by increasing the size of the trap to match the size of the pre-cooled ensemble for optimal loading. Successive fast reduction of the extend of the trap leads to optimal evaporation efficiency and leads to increased sensitivity of the device, due to reduced cycle time of the experiment and increased atom number. Beyond this, the technique allows for new sensor geometries via the creation of multiple single wells, allowing for differential atom interferometry with numerous simultaneous interferometers. In this thesis, the first matter-wave analogue of a classical accelerometer array is implemented via the creation of a 3 × 3 array of Bose-Einstein condensates, consisting of 3 × 105 atoms and spanning a total area of 1.6 mm2 . Successive manipulation of the matter-waves with atom optics, coherently addressing the momentum states of the ensembles, allows for splitting, redirecting and readout pulses, realizing Mach-Zehnder type atom interferometers. Correlation of the nine 1D-acceleration measurements output by the interferometers yields measurements of linear acceleration, Euler- and centrifugal acceleration. The estimated sensitivity limits per shot are 6 × 10−5m s−2 for linear acceleration, 0.19 rad s − 2 for rotational acceleration and 203 mrad s−1 for rotation rate and are mainly limited due to the short free fall time of the ensembles, constrained by the atom optics light field. The correlation also allowed to determine the rotation center, being close to the retro reflection mirror of the atom optics light field. Crucial for the realization of this measurement was the implementation of time averaged potentials as stated above, facilitated through two 2D acousto-optical deflectors and a software defined radio, allowing for generating the required RF-signals. The techniques to simultaneously load and evaporate multiple ensembles into distinct traps from a single cloud of cold atoms and subsequently enlarge the spacing between the ensembles with adiabatic transport ramps are of highest interest for e.g. the Very Long Baseline Atom Interferometer facility in Hannover. Due to the correlated outputs systematic errors, such as wave front abberations, can be nullified. Furthermore the scheme can be extended to 3D matter-wave arrays, fulfilling all requirements necessary for an autonomous inertial measurement unit.
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.
Accelerometer systems that would combine the best features of both conventional (e.g., mechanical) accelerometers and atom interferometer accelerometers (AIAs) have been proposed. These systems are intended mainly for use in scientific research aboard spacecraft but may also be useful on Earth in special military, geological, and civil-engineering applications. Conventional accelerometers can be sensitive, can have high dynamic range, and can have high frequency response, but they lack accuracy and long-term stability. AIAs have low frequency response, but they offer high sensitivity, and high accuracy for measuring small accelerations. In a system according to the proposal, a conventional accelerometer would be used to perform short-term measurements of higher-frequency components of acceleration, while an AIA would be used to provide consistent calibration of, and correction of errors in, the measurements of the conventional accelerometer in the lower-frequency range over the long term. A brief description of an AIA is prerequisite to a meaningful description of a system according to the proposal. An AIA includes a retroreflector next to one end of a cell that contains a cold cloud of atoms in an ultrahigh vacuum. The atoms in the cloud are in free fall. The retroreflector is mounted on the object, the acceleration of which is to be measured. Raman laser beams are directed through the cell from the end opposite the retroreflector, then pass back through the cell after striking the retroreflector. The Raman laser beams together with the cold atoms measure the relative acceleration, through the readout of the AIA, between the cold atoms and the retroreflector.
Inertial sensors based on cold atom interferometry exhibit many interesting features for applications related to inertial navigation, particularly in terms of sensitivity and long-term stability. However, at present the typical atom interferometer is still very much an experiment—consisting of a bulky, static apparatus with a limited dynamic range and high sensitivity to environmental effects. To be compliant with mobile applications further development is needed. In this work, we present a compact and mobile experiment, which we recently used to achieve the first inertial measurements with an atomic accelerometer onboard an aircraft. By integrating classical inertial sensors into our apparatus, we are able to operate the atomic sensor well beyond its standard operating range, corresponding to half of an interference fringe. We report atom-based acceleration measurements along both the horizontal and vertical axes of the aircraft with one-shot sensitivities of 2.3 × 10−4 g over a range of ∼ 0.1 g. The same technology can be used to develop cold-atom gyroscopes, which could surpass the best optical gyroscopes in terms of long-term sensitivity. Our apparatus was also designed to study multi-axis atom interferometry with the goal of realizing a full inertial measurement unit comprised of the three axes of acceleration and rotation. Finally, we present a compact and tunable laser system, which constitutes an essential part of any cold-atom-based sensor. The architecture of the laser is based on phase modulating a single fiber-optic laser diode, and can be tuned over a range of 1 GHz in less than 200 μs.
Atom-interferometric quantum sensors could revolutionize navigation, civil engineering, and Earth observation. However, operation in real-world environments is challenging due to external interference, platform noise, and constraints on size, weight, and power. Here we experimentally demonstrate that tailored light pulses designed using robust control techniques mitigate significant error sources in an atom-interferometric accelerometer. To mimic the effect of unpredictable lateral platform motion, we apply laser-intensity noise that varies up to 20% from pulse-to-pulse. Our robust control solution maintains performant sensing, while the utility of conventional pulses collapses. By measuring local gravity, we show that our robust pulses preserve interferometer scale factor and improve measurement precision by 10× in the presence of this noise. We further validate these enhancements by measuring applied accelerations over a 200 μg range up to 21× more precisely at the highest applied noise level. Our demonstration provides a pathway to improved atom-interferometric inertial sensing in real-world settings.