Multi-Axis Inertial Sensing with 2D Matter-Wave Arrays
Knut Stolzenberg, Christian Struckmann, Sebastian Bode, Rui Li, Alexander Herbst, V. Vollenkemper, D. Thomas, Ashwin Rajagopalan, Ernst Maria Rasel, Naceur Gaaloul, Dennis Schlippert
Atom interferometery is an exquisite measurement technique sensitive to inertial forces. However, it is commonly limited to a single sensitive axis, allowing high-precision multidimensional sensing only through subsequent or postcorrected measurements. We report on a novel method for multi-axis inertial sensing based on the correlation of simultaneous light-pulse atom interferometers in 2D array arrangements of Bose-Einstein condensates (BEC). Deploying a scalable 3×3 BEC array spanning 1.6 mm^{2} created using time-averaged optical potentials, we perform measurements of linear acceleration induced by gravity and simultaneously demonstrate sensitivity to angular velocity and acceleration of a rotating reference mirror, as well as gravity gradients and higher-order derivatives. Our Letter enables simple, high-precision multi-axis inertial sensing compatible with high rotation rates, e.g., for inertial navigation in dynamic environments. We finally envision further applications of our method, e.g., 3D in situ measurements and reconstruction of laser beam intensities and wave fronts.
Atom interferometery is an exquisite measurement technique sensitive to inertial forces. However, it is commonly limited to a single sensitive axis, allowing high-precision multidimensional sensing only through subsequent or postcorrected measurements. We report on a novel method for multi-axis inertial sensing based on the correlation of simultaneous light-pulse atom interferometers in 2D array arrangements of Bose-Einstein condensates (BEC). Deploying a scalable 3×3 BEC array spanning 1.6 mm^{2} created using time-averaged optical potentials, we perform measurements of linear acceleration induced by gravity and simultaneously demonstrate sensitivity to angular velocity and acceleration of a rotating reference mirror, as well as gravity gradients and higher-order derivatives. Our Letter enables simple, high-precision multi-axis inertial sensing compatible with high rotation rates, e.g., for inertial navigation in dynamic environments. We finally envision further applications of our method, e.g., 3D in situ measurements and reconstruction of laser beam intensities and wave fronts.
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.
We propose new multidimensional atom optics that can create coherent superpositions of atomic wave packets along three spatial directions. These tools can be used to generate light-pulse atom interferometers that are simultaneously sensitive to the three components of acceleration and rotation, and we discuss how to isolate these inertial components in a single experimental shot. We also present a new type of atomic gyroscope that is insensitive to parasitic accelerations and initial velocities. The ability to measure the full acceleration and rotation vectors with a compact, high-precision, low-bias inertial sensor could strongly impact the fields of inertial navigation, gravity gradiometry, and gyroscopy.
Matter-wave interferometers show great a potential for improving inertial sensing. The absence of drifts recommends them for a variety of applications in geodesy, navigation, or fundamental physics. Here, ultracold atomic ensembles, featuring a velocity distribution well below the photon recoil velocity, open up new perspectives. In contrast to standard laser cooling methods, they allow to reach better beam-splitting efficiencies and, hence, a higher contrast as well as to reduce systematic uncertainties and biases. Presently, Bose-Einstein condensates (BECs) provide the means to achieve the lowest expansion energies of few picokelvin. Indeed, the momentum distribution of a BEC can be further narrowed after reaching the regime of ballistic expansion, where all mean field energy is converted to kinetic energy, by the application of the delta-kick collimation technique. With such ensembles, Bragg processes can be driven with an efficiency of above 95% as well as Bloch oscillations performed without large atomic losses or dephasing. Both enable efficient large momentum transfer in interferometers to enhance their sensitivity for inertial effects. In a so-called twin-lattice atom interferometers more than thousand photon recoils are used to form compact but sensitive atom interferometers. These methods not only bring in reach extremely accurate gravimeters and accelerometers but also gyroscopes. Like the Sagnac effect in ring laser or fiber gyroscopes, the sensitivity of atom interferometers to rotations increases with the space-time area enclosed by the interferometer. In the case of light interferometers, the latter can be enlarged by forming multiple fiber loops. However, the equivalent for matter-wave interferometers remains an experimental challenge. An atom interferometer with scalable area may be formed in a twin lattice combined with a relaunch mechanism to obtain multi loops as well. Due to this scalability, it offers the perspective of reaching unprecedented sensitivities for rotations in comparably compact sensor head setups. Moreover, atom-chip technologies offer the possibility to generate a BEC and perform delta-kick collimation in a fast and reliable away, paving the way for field-deployable miniaturized atomic devices. Last but not least, the extremely low expansion energies of BECs open up to extend the time atoms spend in the interferometer to tens of seconds. This brings in reach unprecedented sensitivities in space-borne applications such as satellite geodesy.
White-light interferometry enables ambiguity-free localization by synthesizing interference envelopes from multiple optical wavelengths, but no analogous capability has been realized for coherent matter waves. Here we report the first experimental demonstration of multi-wavelength atom interferometry, establishing the matter-wave counterpart of white-light interferometry. By exploiting counter-propagating atomic beams as multi-wavelength matter wave sources and synthesizing interference envelopes from their spectral components, we realize inertial measurements based on envelope localization rather than conventional fringe-phase estimation. The resulting multi-scale interferometric response provides ambiguity-free operation, a well-defined rotational scale factor, and reduced sensitivity to initial phase bias. As a proof of principle, we demonstrate simultaneous dual-axis rotation and acceleration sensing and directly resolve the phase ambiguity that fundamentally limits conventional open-loop atom interferometers. We further measure the Earth's rotation with a relative error of 4.3% and a long-term stability of 93 ppm at an averaging time of 15,000 s. Our results establish multi-wavelength atom interferometry as a new paradigm for coherent matter-wave sensing, extending the principles of white-light interferometry to atom optics and opening new opportunities for inertial sensing, geodesy, precision metrology, and inertial navigation.
Inertial sensors based on cold atoms and light-pulse interferometry exhibit state-of-the-art sensitivity and ultra-low measurement bias that could revolutionize a variety of fields including geophysics and seismology, gravitational wave detection and fundamental tests of gravity, and inertial navigation. In the latter case, cold-atom interferometers are widely considered as breakthrough technology for future autonomous INSs. Nowadays, absolute quantum inertial sensors are available as commercial and field-deployable devices. Yet, their current size and complexity has not yet reached a technology readiness level compatible with mobile applications or plug-and-play operation by non-specialists. These systems are in desperate need of further development and miniaturization. We will present progress beyond these first experiments while exploring new methods relying on 3D matter-wave manipulation that can lead to interferometer geometries that are simultaneously sensitive to accelerations and rotations in 3D and can discern their vector components within a single measurement. These novel innovations produce additional sensitivity to rotations and gravity gradients which has not yet been exploited experimentally and could be a game changing innovation for future atomic sensors. The ability to measure the full acceleration and rotation vectors with a compact, high-precision, low-bias inertial sensor could strongly impact the fields of inertial navigation, gravity gradiometry, and gyroscopy.
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.