Atom-interferometric quantum inertial sensors are promising candidates for inertial navigation systems owing to their high sensitivity and intrinsically low drift. However, their application to next-generation inertial navigation, targeting a drift below 100 m/month, requires exceptionally stringent inertial-sensor bias stability. In conventional Raman atom interferometers based on ground-state hyperfine transitions, suppressing inertial-sensor biases arising from quadratic Zeeman shifts requires highly optimized magnetic shielding. In this work, we propose a Raman atom interferometer based on fine-structure transitions between metastable states of barium, which exhibit a quadratic Zeeman sensitivity approximately three orders of magnitude lower than that of conventional alkali-atom Raman transitions. We show that the proposed scheme increases the allowable spatial gradient of the magnetic-field magnitude by a factor of several tens, thereby relaxing the magnetic-field-control requirements from highly optimized shielding and compensation systems to standard magnetic-field-control techniques. Furthermore, we experimentally demonstrate Mach--Zehnder interference between metastable fine-structure states of barium, validating a key building block of the proposed inertial-sensing scheme.
Atom-interferometric quantum inertial sensors are promising candidates for inertial navigation systems owing to their high sensitivity and intrinsically low drift. However, their application to next-generation inertial navigation, targeting a drift below 100 m/month, requires exceptionally stringent inertial-sensor bias stability. In conventional Raman atom interferometers based on ground-state hyperfine transitions, suppressing inertial-sensor biases arising from quadratic Zeeman shifts requires highly optimized magnetic shielding. In this work, we propose a Raman atom interferometer based on fine-structure transitions between metastable states of barium, which exhibit a quadratic Zeeman sensitivity approximately three orders of magnitude lower than that of conventional alkali-atom Raman transitions. We show that the proposed scheme increases the allowable spatial gradient of the magnetic-field magnitude by a factor of several tens, thereby relaxing the magnetic-field-control requirements from highly optimized shielding and compensation systems to standard magnetic-field-control techniques. Furthermore, we experimentally demonstrate Mach--Zehnder interference between metastable fine-structure states of barium, validating a key building block of the proposed inertial-sensing scheme.
The Department of Defense relies on many platforms that require inertial sensors to operate in Global Positioning System (GPS)–compromised environments to provide or verify navigational data. The current generation of sensors in use are subject to sensitivity limitations and drift errors that can compound significantly over time in GPS-contested areas. Inertial sensors based on atom interferometers could provide navigational data that is significantly more accurate and less prone to drift (and therefore navigational errors). This research builds upon previous work (Manicchia in 2020, Gervis in 2021) in which an atomic interferometer was constructed and studied. In this thesis, I demonstrate a path toward making inertially sensitive measurements with this apparatus. In contrast to the previous work, I use counter-propagating Raman fields that can achieve inertial sensitivity. However, these Raman fields are sensitive to non-trivial transverse velocities of our atom beam. I demonstrate a method to reduce these transverse velocities using an optical molasses, but do not pursue this in the apparatus due to spatial considerations. I explore the difference between Ramsey and spin echo spectroscopies, forms of atomic interference, in co- and counter-propagating configurations, the second of which is inertially sensitive. I also demonstrate that interference is still visible in the counter-propagating geometry, laying the foundation for a fully inertially sensitive interferometer.
We demonstrate a closed-loop light-pulse atom-interferometer inertial sensor that can realize continuous decoupled measurements of acceleration and rotation rate. The sensor operates with double-loop atom interferometers, which share the same Raman light pulses in a spatially separated Mach-Zehnder configuration and use continuous cold atomic beams propagating in opposite directions from two 2D+ magneto-optical trappings. Acceleration and the rotation rate are decoupled and simultaneously measured by the sum and difference of dual-atom-interferometer signals, respectively. The sensitivities of inertial measurements are also increased to be approximately 1.86 times higher than that of a single atom interferometer. The acceleration phase shift is compensated in real time by phase locking these interferometers via the Raman laser phases from the sum-interferometer signal, and the gyroscope performance is improved. We achieve long-term stabilities of $6.1\phantom{\rule{0.2em}{0ex}}\text{\ensuremath{\mu}}\text{g}$ and 840 nrad/s for the acceleration and the rotation rate, respectively, using a short interrogation time of 0.87 ms (interference area A=0.097mm2). This work provides a building block for an atomic interferometer-based inertial measurement unit for use in field applications that require a high data rate and high stability.
The presented thesis describes the setting up of an inertial sensitive atom interferometer for navigation using Rubidium 87 atoms, which is able to perform horizontal acceleration measurement. An ultra-high vacuum interferometer chamber is designed and built. The cold atoms are prepared in a compact 2D MOT setup and loaded into the main MOT. These atoms are then cooled down to few K and prepared in a magnetically insensitive ground state using a sequence of optical and microwave pulses, after which atoms are selected in a narrow band of the velocity. A three-pulse Mach-Zehnder ( pi/2 -pi-pi/2) interferometer using stimulated Raman transitions is used to measure the horizontal acceleration. To improve the sensitivity to acceleration, the fringe contrast of the interferometer requires to be optimised. By investigating the intensity profile of the Raman beams using atoms, a procedure is developed to operate the interferometer in an improved condition, which is able to enhance the fringe contrast by a factor of 3. This procedure improves the shot-to-shot sensitivity of the interferometer below 5 um/s^2. In addition, the atom interferometer is compared with a classical state-of-the-art accelerometer.
A rotation-rate sensor was developed using atom interferometry and the Sagnac effect for matter waves. This device has a short-term sensitivity of 6× 10−10 rad/sec for a 1 second integration time, which is the best publicly reported value to date. It has high intrinsic accuracy because it relies on interactions between atoms and laser light that is stabilized to an atomic transition. Long-term stability is promising and characterization is currently underway. Potential applications include inertial navigation, geophysical studies, and general relativity tests such as verification of the Lense-Thirring and geodetic effects. The principle of operation is as follows: A thermal cesium atomic beam crosses three laser interaction regions where two-photon stimulated Raman transitions between cesium ground states transfer momentum to atoms and divide, deflect, and recombine the atomic wavepackets. Rotation induces a phase shift between the two possible trajectories and causes a change in the detected number of atoms with a particular internal state. Counterpropagating atomic beams form two interferometers using shared lasers for common-mode rejection, and the rotation phase shifts have opposite sign since the phase shift is proportional to the vector velocity of the atoms. Therefore, subtracting or adding the interferometer signals discriminates between rotation and transverse acceleration summed with laser arbitrary phase. Furthermore, in the inertial reference frame of the atoms, rotations Doppler-shift the Raman lasers. Adding Raman frequency shifts to cancel these Doppler-shifts allows operation at an effective zero rotation rate, improving sensitivity and bandwidth. Modulating these frequency shifts facilitates sensitive lock-in detection readout techniques.
Atom interferometric sensors can enable extremely precise measurements of inertial motion and external fields by manipulating and interfering atomic states using pulses of laser light. However, like many experiments that require the coherent control of a quantum system, the interaction fidelity is limited by inhomogeneities in the control fields. Variations in atomic velocity and laser intensity lead different atoms to experience different interactions under the same pulse, reducing the interference fringe contrast, introducing bias, and limiting the sensitivity. We present the theoretical design and experimental demonstration of pulses for atom interferometry which compensate inhomogeneities in atomic velocity and laser intensity. By varying the laser phase throughout a pulse and choosing an appropriate fidelity measure to be maximised, pulses are optimised by adapting optimal control techniques originally designed for nuclear magnetic resonance applications. We show using simulations that optimised pulses significantly improve the fidelity of interferometer operations and verify this experimentally using Raman transitions within a cold sample of 85Rb atoms. We demonstrate a robust state-transfer pulse that achieves a fidelity of 99.8(3)% in a ∼ 35 µK sample and obtain a threefold increase in the fringe contrast using a full sequence of optimised pulses. Many of the pulse shapes found by optimal control are simple and symmetrical, and we show that certain symmetries are integral to error compensation. By systematically exploring the dependence of these solutions on the model and optimisation parameters, we demonstrate a stability which underlines the general applicability of optimised pulses to a range of interferometer configurations. Finally, we introduce and computationally analyse a novel theoretical approach to improve the sensitivity of large-momentum-transfer (LMT) interferometers, whereby “biselective” pulses are optimised to track the changing resonance conditions encountered in extended pulse sequences that are designed to increase the measurement sensitivity. When conventional pulses of steady phase are used, the interference contrast decays rapidly as extra pulses are added because of the change in resonance. Using numerical simulations, we show that bi-selective pulses maintain interaction fidelity throughout extended pulse sequences, allowing significant increases in the sensitivity that may be obtained using LMT.
The utilization of light-pulse atom interferometry presents a valuable technique that has found application in both fundamental scientific inquiries, such as investigating constants such as measurements of fine structure constant α and gravitational constant G, and practical endeavors including acceleration sensing and rotation measurements. This thesis delves into our implementation of a dual atom interferometer design involving the clock transition 1S0 → 3P0 in strontium, concurrently conducting the interferometric sequence on atoms in both ground and excited states. To facilitate the dual atom interferometer’s operation, we have firstly established a compact experimental setup with a transversely loaded bi-dimensional magneto-optical-trap (2D-MOT) to create a high flux source of cold strontium atoms. Introducing a novel cross-polarized bi-color atomic beam slower, we simultaneously addresses two excited Zeeman substates of the transition 1S0 → 1P1 in strontium-88, significantly enhancing the number of atoms prepared in the 461 nm MOT by around 10-fold. Following the 461 nm MOT, the atomic ensemble undergoes cooling in a 689 nm MOT, achieving atomic temperatures below 1 µK. We also install a network of eight magnetic field probes arranged around the cold atomic sample, enabling precise three-axis active control of magnetic fields down to the milligauss level. With the atoms confined in a 2D lattice at the magic-wavelength of 813.427 nm after the initial preparation phase, we conduct the magnetically-induced clock transition to create a statistical mixture state of ground and excited states. After a velocity selection stage, implementing a Mach-Zehnder interferometer with Bragg pulses operating at the magic-wavelength along the vertical axis, we conduct tests of the weak equivalence principle (WEP). The Eötvös ratio we found in our system stood at (1.8 ± 3.1) × 10−4, mainly limited by the finite temperature of the atomic cloud constraining the interrogation time. Furthermore, the dual atom interferometer scheme enables the measurement of state-dependent force and eventually polarizability difference via the phase shift between the atoms in different states, and we experimentally demonstrate this by introducing an additional light field gradient.