Two kinds of multidimensional atom interferometers are demonstrated that are capable of measuring both the magnitude and direction of applied inertial forces. These interferometers, built from ultracold Bose-Einstein condensed rubidium atoms, use an original design that operates entirely within the Bloch bands of an optical lattice. Through time-dependent lattice position control, we realize Bloch oscillations in two dimensions and a vector atomic Michelson interferometer. Fits to the observed Bloch oscillations demonstrate the measurement of an applied acceleration of 2 g along two axes, where g is Earth’s gravitational acceleration. For the Michelson interferometer, we perform Bayesian inferencing from a 49-channel output by repeating experiments for two-axis accelerations and demonstrate vector parameter estimation. Accelerations can be measured from single experimental runs and do not require repeated shots to construct a fringe. The performance of our device is near the quantum limit for the interferometer size and quantum detection efficiency of the atoms.
Two kinds of multidimensional atom interferometers are demonstrated that are capable of measuring both the magnitude and direction of applied inertial forces. These interferometers, built from ultracold Bose-Einstein condensed rubidium atoms, use an original design that operates entirely within the Bloch bands of an optical lattice. Through time-dependent lattice position control, we realize Bloch oscillations in two dimensions and a vector atomic Michelson interferometer. Fits to the observed Bloch oscillations demonstrate the measurement of an applied acceleration of 2 g along two axes, where g is Earth’s gravitational acceleration. For the Michelson interferometer, we perform Bayesian inferencing from a 49-channel output by repeating experiments for two-axis accelerations and demonstrate vector parameter estimation. Accelerations can be measured from single experimental runs and do not require repeated shots to construct a fringe. The performance of our device is near the quantum limit for the interferometer size and quantum detection efficiency of the atoms.
The creation of a matter-wave interferometer can be achieved by loading Bose-Einstein condensed atoms into an optical lattice. By shaking the lattice via either phase or frequency modulation, the traditional steps of interferometry; splitting, propagating, reflecting, again propagating and then recombining the atomic wavefunction, can be implemented, allowing for the sensing of broad range of inertial signals. This approach is interesting, since the atoms can be supported against external forces and perturbations, and the system can be completely reconfigurable on-the-fly for a new design goal. We report on theoretical and experimental results in which atoms are cooled to degeneracy in a dipole trap and subsequently loaded into a multidimensional optical lattice. Shaking protocols for obtaining interferometry steps are derived via machine-design approaches consisting of machine learning and quantum optimal control. Experimental confirmation of the designed operation of a two-dimensional vector accelerometer is shown and its performance to applied accelerations measured. Both the direction and magnitude of the applied signal is varied and validation of both scenarios presented.
Atom interferometers exploit the wave nature of matter to measure inertial forces with high precision, but conventional light-pulse implementations typically require large free-fall distances and complex optical systems. Bloch-band interferometry offers an alternative architecture in which atoms remain confined within an optical lattice and interferometric operations are implemented through controlled transitions between Bloch bands. This thesis investigates Bloch-band interferometry with particular emphasis on robustness to phase decoherence and operation in the deep-lattice regime. The work begins with multi-well models that provide intuition for tunneling, interference, and phase coherence. Phase scrambling was introduced to model loss of coherence, demonstrating that interference contrast is reduced but not eliminated. These insights motivated a full momentum-space simulation of a Bloch-band Michelson interferometer, including splitting, transport, reflection, and recombination. Acceleration scans with site-to-site phase randomness showed that interferometric fringes and sensitivity persist even with reduced coherence. Building on this robustness, Bloch-band interferometry was extended to a deep optical lattice with depth of 27 times the recoil energy. Higher Bloch bands were used to define interferometric pathways, and machine-learned shaking functions were implemented to realize beamsplitter and mirror operations. The resulting deep-lattice interferometer exhibits acceleration-dependent population fringes and measurable sensitivity. To our knowledge, this work presents the first exploration of Bloch-band interferometry in the deep-lattice regime and demonstrates the first realization of a deep-lattice Bloch-band interferometer for inertial sensing. These results suggest that Bloch-band interferometry can remain operational in regimes approaching the insulating limit, providing a potential route toward compact and robust quantum inertial sensors.
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.
Atom interferometers are quantum mechanical devices sensitive to gravitational and inertial forces, with applications in fundamental physics and inertial sensing in the field. Their performance is currently limited by the interrogation time available to freely falling atoms in Earth’s gravitational field, as well as noise due to mechanical and acoustic vibrations. Our experiment probes gravitational potentials by holding, rather than dropping, atoms. We realize an interrogation time of 20 seconds by suspending the spatially separated atomic wave packets in an optical lattice. This record coherence is enabled by the smooth lattice wave fronts, which are mode-filtered by an optical cavity. This trapped geometry suppresses phase variance due to vibrations by three to four orders of magnitude, overcoming the dominant noise source in atom-interferometric gravimeters. The later part of the talk describes recent progress in characterizing and reducing dephasing of the interferometer. An upgraded optical lattice interferometer experiment is currently being commissioned, with the goal of increased sensitivity to gravity.
Precision interferometry with atomic wavepackets confined in a one-dimensional optical lattice is an emergent paradigm in quantum sensing of forces and fields, with applications in gravimetry, accelerometry, geophysics, and fundamental physics tests. We report on the realization of a lattice-trapped interferometer where the two arms are sourced from a weakly-interacting ytterbium Bose-Einstein condensate, coherently split and trapped by pulsed optical standing waves before recombination. We directly observe atomic interactions through contrast changes and phase shifts of the interferometer. By changing either the atom number or the sample volume to vary the density, we demonstrate control over interactions and optimize interferometer performance. Our observations are effectively captured by a mean-field theoretical model of the system. This work experimentally probes the boundary where improved performance from source brightening through higher phase space density transitions into a regime beyond single-atom physics in lattice-trapped atom interferometry, and opens a door to incorporating many-body effects for metrological advances in such platforms.
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.