Atom interferometry is a powerful metrological tool that has been developed over the last few decades. Large momentum transfer (LMT) methodsmanipulate atomic trajectories with tens or hundreds of photon momenta\nin order to increase sensitivity. This thesis furthers progress towards using\nLMT methods in next-generation atom interferometers. One main result establishes symmetric Bloch oscillations as a new, viable technique for LMT.\nTheory and numerics are used to show how the process is coherent and\nadiabatic, and experimentally we demonstrate coherence in an interferometer with up to 240¯hk, where ¯hk is the momentum of a single photon of\n852nm light. This was the second largest coherent momentum splitting\ndemonstrated at at the time of publication. The rest of the thesis focuses\non design and construction of a new atomic fountain to measure the fine\nstructure constant α. Discrepancies in recent measurements of α [67, 55]\nare currently limiting theory predictions for the electron gyromagnetic ratio\n[25] - an improved measurement of α is therefore highly motivated and would\nenable an improved test of the consistency of the Standard Model. Previously, our group published a measurement of α at the 0.2 ppb level in 2018\n[67]. We built a new experiment with a goal of improving the measurement\nby a factor of 3-10. Much of the thesis focuses on systematic effects related\nto spatial intensity inhomogeneities on the laser beam, which are some of\nthe hardest to characterize systematic effects looking forward. A large clear\naperture vacuum chamber accommodates larger waist laser beams without\nclipping on chamber walls. In addition, a high-speed, user-friendly Monte\nCarlo simulation package was made to predict experimental systematic shifts\nin the measured value of α due to laser beam inhomogeneities.
Atom interferometry is a powerful metrological tool that has been developed over the last few decades. Large momentum transfer (LMT) methodsmanipulate atomic trajectories with tens or hundreds of photon momenta\nin order to increase sensitivity. This thesis furthers progress towards using\nLMT methods in next-generation atom interferometers. One main result establishes symmetric Bloch oscillations as a new, viable technique for LMT.\nTheory and numerics are used to show how the process is coherent and\nadiabatic, and experimentally we demonstrate coherence in an interferometer with up to 240¯hk, where ¯hk is the momentum of a single photon of\n852nm light. This was the second largest coherent momentum splitting\ndemonstrated at at the time of publication. The rest of the thesis focuses\non design and construction of a new atomic fountain to measure the fine\nstructure constant α. Discrepancies in recent measurements of α [67, 55]\nare currently limiting theory predictions for the electron gyromagnetic ratio\n[25] - an improved measurement of α is therefore highly motivated and would\nenable an improved test of the consistency of the Standard Model. Previously, our group published a measurement of α at the 0.2 ppb level in 2018\n[67]. We built a new experiment with a goal of improving the measurement\nby a factor of 3-10. Much of the thesis focuses on systematic effects related\nto spatial intensity inhomogeneities on the laser beam, which are some of\nthe hardest to characterize systematic effects looking forward. A large clear\naperture vacuum chamber accommodates larger waist laser beams without\nclipping on chamber walls. In addition, a high-speed, user-friendly Monte\nCarlo simulation package was made to predict experimental systematic shifts\nin the measured value of α due to laser beam inhomogeneities.
We experimentally and theoretically study Bragg diffraction as a tool for large-momentum transfer beam splitters in atom interferometry. A theoretical framework is developed to quantify the diffraction phase systematic caused by Bragg diffraction and experiments are performed to confirm these predictions using a Ramsey-Bord\\'e atom interferometer. We then develop methods to systematically cancel and reduce the diffraction phase systematic by carefully selecting Bragg diffraction parameters and utilizing Bloch oscillations. These techniques are then applied to an ongoing precision measurement of $h/m_\\text{Cs}$ for cesium, with the end goal of measuring the fine structure constant alpha. We demonstrate a high contrast simultaneous conjugate Ramsey-Bord\\'e interferometer using 5th order Bragg diffraction and 25 common mode Bloch oscillations which achieves 2.5times106 radians of phase. We also demonstrate an interferometer with a statistical uncertainty of deltaalpha/alpha=0.25 ppb after 25 hours of integration time that has diffraction phase systematic error of around 1 ppb. Other sources of systematic uncertainty are also thoroughly explored and determined to better than 0.1 ppb. The techniques and theories developed in this thesis will hopefully help enable future precision measurements based on Bragg diffraction.
The leading experimental determinations of the fine-structure constant α currently rely on atomic photon-recoil measurements from Ramsey-Bordé atom interferometry with large-momentum transfer to provide an absolute mass measurement. We propose an experimental scheme for an intermediate-scale differential atom interferometer to measure the photon recoil of neutral atomic species with a single-photon optical clock transition. We calculate trajectories for our scheme that optimize the recoil phase while nullifying the undesired gravity-gradient phase by considering independently launching two clouds of ultracold atoms with the appropriate initial conditions. For Sr and Yb, we find an atom interferometer of height 3 m to be sufficient for an absolute mass measurement precision of Δ m / m ∼ 1 × 10 − 11 with current technology. Such a precise measurement would halve the current uncertainty in α , an uncertainty that would no longer be limited by an absolute mass measurement. The removal of this limitation would allow the current uncertainty in α to be reduced by a factor of 10 by corresponding improvements in relative mass measurements, thus paving the way for higher-precision tests of the standard model of particle physics. Published by the American Physical Society 2024
The fine structure constant can be determined from the measurement of the ratio h/m between the Planck constant, h, and the mass of an atom, m. The comparison of the experimental value of the anomalous magnetic moment of the electron or the muon with their theoretical values predicted by the Standard Model using this value of the fine structure constant allows a very precise test of this model. My thesis work focused principally on the measurement of the h/m ratio of rubidium-87 using a new experimental device. This device has been designed to produce an ultra-cold source by evaporation in an all-optical dipole trap loaded from optical molasses. We optimized the parameters of the experimental device using a genetic algorithm, which allowed us to produce a Bose Einstein condensate, containing 120,000 atoms, polarized in the state F=1, mF=0, with a cycle time of 3.5 seconds. We then installed the laser device for atom interferometry, to interrogate a cloud of cold atoms produced by optical molasses. Combining an interferometer using Raman transitions and the Bloch oscillation technique, we demonstrated an unprecedented sensitivity on the measurement of h/m corresponding to a relative statistical uncertainty of 8.5 x 10-11 in 48 hours of integration, or 4.3 x 10-11 on the fine structure constant. This sensitivity has allowed us to experimentally study a variety of systematic effects. We simultaneously carried out modelling work that contributed to the implementation of protocols to compensate for the biases induced by systematic effects. We present a preliminary assessment of the error budget associated with these effects.
Light-pulse atom interferometers have been used as quantum inertial sensors and for precision tests of fundamental laws of physics. For higher contrast, we apply conjugate Ramsey-Borde interferometers to cancel out vibrational noise and top mirror tilting to compensate the Coriolis force. For higher sensitivity, we implement Bragg diffraction and Bloch oscillations for large momentum transfer to increase the enclosed area of our atom interferometer. We also utilize Raman sideband cooling in our experimental setup, which increases the overall signal about twentyfold, and increases the contrast by suppressing the thermal expansion of the atom cloud.By combining measurements of recoil frequency and a frequency comb, we present the first clock referenced to the mass of a single particle. The rest mass of a particle defines its Compton frequency, mc^2/h through relativity and quantum mechanics, and thereby sets a fundamental timescale. Our clock stabilizes a 10 MHz radio frequency signal to a certain fraction of the cesium Compton frequency. Future work could result in an elementary particle (electron) or even antimatter (antihydrogen) clock, opening up new ways to test CPT symmetry and the equivalence principle. We also present our progress towards a new determination of the fine structure constant. The fine structure constant value obtained by our cesium Compton clock measurement is about three times better compared with the earlier cesium recoil frequency result. After combining Bragg diffraction and Bloch oscillations, we achieved 0.33 ppb sensitivity (0.66 ppb uncertainty of the recoil frequency measurement) in 6 hours, which is about two times better than the previous best recoil frequency measurement. The leading systematic effect is also reduced by a factor of 2.75.
The main subject of this thesis is to demonstrate that helium is a promising candidate for matter wave interferometry, with the goal of providing an improved value for the fine-structure constant, α. In particular, fast and efficient momentum transfer via Bloch oscillations in an optical lattice is demonstrated, together with the enhanced sensitivity offered by an ion-detector based detection scheme that is unique to metastable helium (He*). The experiments are performed in a setup that was built to produce, slow down and trap ultracold (~0.2 μK) He-4 atoms. The approach to realising an ultracold sample of He* atoms consists of a sequence of trapping and cooling stages. The experiment starts at the plasma discharge source, where helium atoms are excited to the so-called metastable 2-3S1 state, with a lifetime of ~7800 seconds, 20 eV above the atomic ground state. The atomic beam exiting from the source is 2-D collimated by 1083 nm laser light, resonant to the closed 2-3S1 - 2-3P2 cooling transition. Next, the atoms are slowed down from about 1000- to 50 m/s in a two meter long Zeeman slower through continuous absorption of resonant 1083 nm light. The slowed atoms are captured in a Magneto-Optical Trap (MOT), that holds up to 5x10^8 atoms at a temperature of 1 mK. The MOT cloud is compressed, spin-polarised and transferred to a cloverleaf Magnetic Trap (MT), which provides both axial and radial trapping through a set of coils outside the vacuum. In the MT, 1D-Doppler cooling is applied to the atomic sample to reduce the temperature to about 150 μK. Following this step, the temperature is reduced further by forced evaporative radio-frequency cooling, resulting in the onset of a Bose-Einstein Condensate (BEC). The atoms are transferred from the MT to a crossed horizontal optical dipole trap (ODT), in which the sample is further evaporatively cooled to produce a BEC of 5x10^6 atoms. The BEC is then transferred from the ODT to either a horizontal or vertical optical lattice, consisting of two counter-propagating laser beams at 1557 nm. By detuning the frequency of one of the lattice beams, the standing wave can be accelerated. The trapped helium atoms can follow the accelerating lattice through a process called Bloch oscillations (BO's), which describes the behaviour of particles in a periodic potential that are subjected to a force. Specifically, in this scenario, particles' velocities increase in increments of two recoil velocities, instead of continuously. Bloch oscillations of cold atoms in periodic potentials formed by optical lattices were first studied in 1996. Importantly, BO’s provide a way to efficiently accelerate atoms by coherently transferring a well controlled, large number of photon momenta, which has been used to increase the resolution of recoil measurements with caesium and rubidium atoms. In this thesis, Bloch oscillations with a metastable helium BEC are demonstrated. Due to its light mass, helium can be efficiently accelerated to high velocities which makes it a candidate for experiments that benefit from splitting the atomic wave-function over large distances. Additionally, Rabi-oscillations in an optical lattice are shown, which serve to probe the depth of the lattice, and a measurement of gravity through Bloch oscillations in a static vertical optical lattice is demonstrated, with a statistical uncertainty of 4x10^-5. Finally, the first proof of principle demonstration of a pulsed light He* atom interferometer is shown. The measurements illustrate the high signal-to-noise that can be obtained using an MCP detector. Next to that, we have demonstrated a method for determining the polarizability of atoms at specific wavelengths, by observing the induced change of the characteristic Bloch oscillation frequency by introducing that wavelength to the system.
We demonstrate atom interferometers utilizing a novel beam splitter based on sequential multiphoton Bragg diffractions. With this sequential Bragg large momentum transfer (SB-LMT) beam splitter, we achieve high contrast atom interferometers with momentum splittings of up to 102 photon recoil momenta (102ℏk). To our knowledge, this is the highest momentum splitting achieved in any atom interferometer, advancing the state-of-the-art by an order of magnitude. We also demonstrate strong noise correlation between two simultaneous SB-LMT interferometers, which alleviates the need for ultralow noise lasers and ultrastable inertial environments in some future applications. Our method is intrinsically scalable and can be used to dramatically increase the sensitivity of atom interferometers in a wide range of applications, including inertial sensing, measuring the fine structure constant, and detecting gravitational waves.