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.
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
Ushered forth by advances in time and frequency metrology, atom interferometry remains an indispensable measurement tool in atomic physics due to its precision and versatility. A sequence of four
pi/2 beam splitter pulses can create either an interferometer sensitive to the atom's recoil frequency when the momentum imparted by the light reverses direction between pulse pairs or, when constructed from pulses without such reversal, sensitive to the perturbing potential from an external optical field. Here, we demonstrate the first atom interferometer with laser-cooled lithium, advantageous for its low mass and simple atomic structure. We study both a recoil-sensitive Ramsey-Bord\\'e interferometer and interferometry sensitive to the dynamic polarizability of the ground state of lithium. Recoil-sensitive Ramsey-Bord\\'e interferometry benefits from lithium's high recoil frequency, a consequence of its low mass. At an interrogation time of 10 ms, a Ramsey-Bord\\'e lithium interferometer could achieve sensitivities comparable to those realized at much longer times with heavier alkali atoms. However, in contrast with other atoms that are used for atom interferometry, lithium's unresolved excited-state hyperfine structure precludes the the cycling transition necessary for efficient cooling. Without sub-Doppler cooling techniques. As as result, a lithium atomic gas is typically laser cooled to temperatures around 300
muK, above the Doppler limit, and well above the recoil temperature of 6
muK. This higher temperature gas expands rapidly during the operation of an atom interferometer, limiting the experimental interrogation time and preventing spatially resolved detection. In this work, a light-pulse lithium matter-wave interferometer is demonstrated in spite of these limitation. Two-photon Raman interferometer pulses coherently couple the atom's spin and momentum and are thus able to spectrally resolve the outputs. These fast pulses drive conjugate interferometers simultaneously which beat with a fast frequency component proportional to the atomic recoil frequency and an envelope modulated by the two-photon detuning of the Raman transition. We detect the summed signal at short experimental times, preventing perturbation of the signal from vibration noise. This demonstration of a sub-recoil measurement with a super-recoil sample opens the door to similar scheme with other particles that are difficult to trap and cool well, like electrons. An interferometer instead composed of
pi/2-pulses with a single direction of momentum transfer, can be sensitive to the dynamic polarizability of the atomic ground state. By scanning the frequency of an external driving field, such a measurement can be used to determine the atom's tune-out wavelength. This is the wavelength at which the frequency-dependent polarizability vanishes due to compensating ac-Stark shifts from other atomic states. Lithium's simple atomic structure allows for a precise computation of properties with only {\\em ab initio} wave functions and spectroscopic data. A direct interferometric measurement of lithium's red tune-out wavelength at 670.971626(1) nm, is a precise comparison to existing `all-order' atomic theory computations. It also provides another way to experimentally determine the
S− to
P− transitions matrix elements, for which large correlations and small values complicate computations. Finally, a future measurement of lithium's ultraviolet tune-out wavelength of at 324.192(2) nm would be sensitive to relativistic approximations in the atomic structure description.Atom interferometry simultaneously verifies existing atomic theory with measurements of atomic properties and searches for exotic physics lurking in plain sight. The techniques developed here broaden the applicability of interferometry and increase measurement sensitivity by simplifying cooling, increasing atom number and reducing the cycle time. Overcoming the current experimental limitations on interrogation time would allow for ultra-precise measurements of both the tune-out wavelength and the fine structure constant.
We report a first realization of cold atom interferometers with the lightest alkali metal
6Li atoms and precisely measure the recoil frequency. The atoms are cooled to approach the half of the photon-recoil limit by using a narrow $2S\ensuremath{\rightarrow}3P$ ultraviolet transition. A ``magic'' magnetically insensitive state, a high-efficiency state preparation, and a frequency-insensitive Raman coupling are developed to overcome the challenges from the half-integer spin and hyperfine interaction of atoms. A conjugated $\text{Ramsey-Bord}\stackrel{\ifmmode \acute{}\else \'{}\fi{}}{\mathrm{e}}$ interferometer with crossed Raman beams is realized with a coherence time longer than 2.3 ms. The four sets of interferometers developed using geometric relations greatly eliminate the error from the angle between Raman beams. The measured recoil frequency is ${\ensuremath{\omega}}_{r}=2\ensuremath{\pi}\ifmmode\times\else\texttimes\fi{}73\phantom{\rule{0.16em}{0ex}}672.789\phantom{\rule{0.16em}{0ex}}(36)$ Hz, representing the most precise measurement of the recoil frequency of
6Li by using the atom interferometer so far. The realized
6Li cold atom interferometer is not only an effective supplement to the existing interferometers, but also provides a good candidate in precision measurement owing to its low mass and high recoil frequency.
We report on our experiment to measure h/M, the ratio of the Planck constant to the mass of Cs atoms, and thereby the fine‐structure constant. The target accuracy is 1 part per billion or better. We focus on two recent milestones: (i) The first realization of atom interferometers based on light‐pulse beam splitters that transfer the momentum of up to 12 photon pairs, which increases the useful signal (matter wave phase shift) by a factor of 144 compared to the beam splitters used in the best present atom interferometers. Moreover, they lead to a cancellation of important systematic effects. (ii) The first realization of a simultaneous pair of conjugate Ramsey‐Bordé interferometers. In these, the relative sign of the inertial term is reversed so that it can be cancelled. Simultaneous operation means that this holds for a time‐dependent inertial term (vibrations) too, which promises a substantial improvement in the signal to noise ratio.
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.