Atom-based sensors have the potential to enhance inertial navigation in Global Positioning System (GPS)-denied environments, providing an alternative to traditional accelerometers, gyroscopes, and sensors. Accurate temperature characterization is critical for atom interferometry, which relies on precise control of atomic motion to achieve high sensitivity. This research develops a model to infer the temperature of laser-cooled rubidium vapor by analyzing its ballistic expansion. The release and recapture method is employed to track atomic cloud dynamics after trap release, refining temperature inference through comparison with theoretical models. A magneto-optical trap is used to cool and confine the atoms, followed by sub-Doppler cooling to achieve lower temperatures. By characterizing expansion dynamics, this study improves temperature measurement techniques for cold atomic samples, addressing sources of systematic uncertainty that affect precision in quantum sensors. These findings contribute to advancements in laser cooling methodologies and atomic interferometry at the Naval Postgraduate School, with direct defense applications in inertial navigation, precision measurement, and sensing.
Atom-based sensors have the potential to enhance inertial navigation in Global Positioning System (GPS)-denied environments, providing an alternative to traditional accelerometers, gyroscopes, and sensors. Accurate temperature characterization is critical for atom interferometry, which relies on precise control of atomic motion to achieve high sensitivity. This research develops a model to infer the temperature of laser-cooled rubidium vapor by analyzing its ballistic expansion. The release and recapture method is employed to track atomic cloud dynamics after trap release, refining temperature inference through comparison with theoretical models. A magneto-optical trap is used to cool and confine the atoms, followed by sub-Doppler cooling to achieve lower temperatures. By characterizing expansion dynamics, this study improves temperature measurement techniques for cold atomic samples, addressing sources of systematic uncertainty that affect precision in quantum sensors. These findings contribute to advancements in laser cooling methodologies and atomic interferometry at the Naval Postgraduate School, with direct defense applications in inertial navigation, precision measurement, and sensing.
We have performed release-recapture temperature measurements of laser-cooled 85Rb atoms using an optical nanofibre (ONF) in a magneto-optical trap (MOT). The effects of changing the cooling laser light-shift parameter on the temperature of the cold atoms and spring constant of the trap are studied. By varying the cold atom number density near the ONF, the onset of the multiple scattering regime is observed without the need for an estimation of the atom cloud size. Moreover, this sensitive ONF assisted release-recapture technique is easily able to detect any optical misalignment of the cooling laser beams in the MOT. Keywords: laser cooling, optical nanofiber, rubidium, release-recapture, temperature
Ultracold samples of laser-cooled atoms are quantum systems over which modern atomic physicists can exert exquisite control. Largely decoupled from their environment, they can act as near-ideal test masses for inertial sensors based on atom interferometry and are well suited to experiments in coherent control of quantum systems that probe the fundamental nature of quantum mechanics and pave the way for practical quantum simulation and computation. This thesis details a series of experimental results that arise from the coherent control of rubidium atoms with laser light, focusing on the interplay between these interactions and atomic velocities; the laser frequency an atom ‘sees’ is Doppler shifted according to its velocity, while conservation of momentum dictates that, in exchanging photons with a laser, an atom’s velocity is altered. Coherent light–atom interactions can thus be tailored either to measure or to narrow the spread of velocities in an ultracold atomic gas. Alternatively, it can be desirable to design interactions that are homogeneous across a large spread of atomic velocities. All of these aspects are explored in this thesis. The velocity-sensitive interactions that lie at the heart of atom-interferometric inertial sensors are reexamined in a manner that yields considerable insight into the underlying processes and culminates in a novel, precise and elegant technique for measuring the velocity of ultracold atoms that is used to reveal the Gaussian nature of the velocity spread in a cloud with an effective temperature of 18.7(6) µK, undistorted by artefacts that plague other methods. Furthermore, optimal control techniques are applied to the problem of coherently and uniformly manipulating the quantum states of atoms in an ensemble with a large spread of velocities, even subject to variations in laser intensity. A broadband inversion pulse is demonstrated to change the internal state of 99.8(3) % of atoms in a ∼35 µK ensemble and — for the first time — this technique is used to optimise an entire atom interferometry sequence, yielding a threefold enhancement in the measurement contrast. Finally, a version of grey molasses cooling — in which atoms accumulate in velocity-dependent ‘dark’ states, narrowing their momentum spread and increasing their phase space density — is demonstrated with phase-coherent cooling beams; dark states that exist in this system prove to be particularly resilient to the spatially varying light shifts that are present in an optical dipole trap, and this is used both to enhance the number of atoms loaded into such a trap — by a factor of 7 compared to loading from a conventional optical molasses — and to further cool them once they are loaded in a technique that has promising prospects for the rapid production of ultracold, trapped, atoms.
Abstract The precision measurement of acceleration due to gravity (g) for potential scientific and industrial applications requires the use of absolute quantum gravimeters (AQGs) as quantum sensors. In this study, the development of magneto-optical trap (MOT) for the Rubidium-87 ( 87 Rb) atoms for integration into an atomic gravimeter has been discussed. The MOT serves as a critical component for the cooling and trapping of neutral atoms, providing a high flux, low temperature atomic ensemble for subsequent measurements in cold atomic physics, such as inertial navigation, exploration, and gravity mapping. Our setup emphasizes compactness without compromising atom number or temperature performance using the single 780 nm extended cavity diode laser. We have presented the optimized optical layout for efficient atom cooling, trapping, and detection. The obtained results show atom loading rate of ∼6.02 × 10 8 atoms within 221 ms that provides fast data acquisition for the entire cycle of AQG. The fluorescence signal from free falling MOT is also obtained, which provides time-of-flight of 211 ms and temperature of 57 μK. The system is robust against environmental perturbation and offers valuable insights into the advancement of atomic ensemble for the realization of high precision quantum sensors for geophysical and navigation applications.
Current sensors used for inertial navigation are based on technology with inherent sensitivity limitations. Atom interferometry is a very promising replacement, which could yield many orders of magnitude of improvement in sensitivity, leading to more accurate navigation over longer periods of time relative to current technology. This research investigates the physics of atom interferometry through the construction and characterization of an atomic accelerometer/gyroscope combination. In contrast to current state-of-the-art atomic sensors, which use pulsed cold atom sources and pulsed laser beams, the apparatus investigated relies purely on continuous atomic and laser beams. These differences would result in a sensor that lends itself more readily to smaller sizing, lower power consumption, and reduced complexity. This change in approach to atomic interferometry also introduces challenges resulting from laser and atomic beam divergences and the velocity averaging due to both longitudinal and transverse temperature, which this dissertation shows how to overcome. The work contained herein explores many stages of construction of an atomic gyro including the demonstration and characterization of two-dimensional laser cooling of atoms, stimulated Raman transitions, and Ramsey and spin echo interference. The implications for future research are also outlined and discussed.
Research interest in designing sources of cold atoms has significantly increased during the past ten years with the development of suitable laser sources for magneto-optical trapping and the further mastering of evaporative cooling in order to achieve Bose-Einstein condensation. The magneto-optical trap is now viewed as a standard research facility worldwide and has opened up many new exciting research directions in atomic physics. One area of interest is that of combining spherical microcavities with cold atomic sources in order to achieve efficient photon exchange between the cavity and atom for further understandings of cavity quantum electrodynamics. This could eventually lead to atom entanglement via photon exchange which would have implications for quantum logic design. However, initial attempts to achieve such interactions have been hindered by inadequate control and manipulation of the cold atom source. Here, we present work on designing and building an ultra-stable source of magneto-optically cooled rubidium atoms with a temperature in the tens of microKelvin range. We discuss the different cooling mechanisms involved in the process and present a suitable experimental arrangement including details on the ultra-high vacuum chamber, the laser systems being used and the source of rubidium vapour. Finally, we discuss some future direction for the research including the diffraction of atoms from gratings and micron-sized objects and the parameter control of the cloud of atoms.
Atom interferometry has hugely benefitted from advances made in cold atom physics over the past twenty years, and ultra-precise quantum sensors are now available for a wide range of applications [1]. In particular, cold atom interferometers have shown excellent performances in the field of acceleration and rotation measurements [2,3], and are foreseen as promising candidates for navigation, geophysics, geo-prospecting and tests of fundamental physics such as the Universality of Free Fall (UFF). In order to carry out a test of the UFF with atoms as test masses, one needs to compare precisely the accelerations of two atoms with different masses as they fall in the Earth’s gravitational field. The sensitivity of atom interferometers scales like the square of the time during which the atoms are in free fall, and on ground this interrogation time is limited by the size of the experimental setup to a fraction of a second. Sending an atom interferometer in space would allow for several seconds of excellent free-fall conditions, and tests of the UFF could be carried out with precisions as low as 10-15 [4]. However, cold atoms experiments rely on complex laser systems, which are needed to cool down and manipulate the atoms, and these systems are usually very sensitive to temperature fluctuations and vibrations. In addition, when operating an inertial sensor, vibrations are a major issue, as they deteriorate the performances of the instrument. This is why cold atom interferometers are usually used in ground based facilities, which provide stable enough environments. In order to carry out airborne or space-borne measurements, one has to design an instrument which is both compact and stable, and such that vibrations induced by the platform will not deteriorate the sensitivity of the sensor. We report on the operation of an atom interferometer on board a plane carrying out parabolic flights (Airbus A300 Zero-G, operated by Novespace). We have constructed a compact and stable laser setup, which is well suited for onboard applications. Our goal is to implement a dual-species Rb-K atom interferometer in order to carry out a test of the UFF in the plane. In this perspective, we are designing a dual-wavelength laser source, which will enable us to cool down and coherently manipulate the quantum states of both atoms. We have successfully tested a preliminary version of the source and obtained a double species magneto-optical trap (MOT).