Master of Science, Miami University, 2024, Physics

This thesis presents a first demonstration of the suppression of cross-coupling between transverse degrees of freedom in a two-dimensional cold atom ratchet. Under ideal conditions, motion along each transverse degree of freedom is unaffected by driving(s) along the other axes of the system. In the case of a two-dimensional cold atom ratchet, where environmental noise in the form of photon recoils plays a critical role in the directed propagation of atoms, two-dimensional motion is difficult to control or predict due to highly nonlinear coupling between the driving along one axis and the resulting motion along the other. Here, atomic ratcheting is induced via a harmonic mixing of AC driving forces which produce motion without imparting any net force upon the atoms. When driving along both axes, these drivings may interfere with one another to produce additional, unwanted frequency mixing effects. However, this coupling may be suppressed through the use of quasi-periodic driving, where the driving frequencies applied along each axis are made incommensurate (i.e. the ratio ωx/ωy is made irrational). In addition to the primary result above, this work also investigates resonant activation induced ratcheting and the resulting interplay between harmonic mixing and resonant activation.

Committee: Samir Bali (Advisor); Imran Mirza (Committee Member); E. Carlo Samson (Committee Member) Subjects: Physics; Quantum Physics

Master of Science, Miami University, 2023, Physics

We infer the damping coefficient of cold atoms in a magneto-optical trap by capturing images of the expanding atomic cloud in optical molasses, followed by a measurement of the diffusion constant and temperature. In order to verify our inferred value obtained for the damping coefficient, we attempt to measure the damping coefficient using an alternative experiment. By introducing a perturbing force from an applied bias magnetic field, that shifts the atom cloud's center of mass. A measurement of the characteristic time taken by the cloud to spatially relax back to its equilibrium position permits us to deduce the damping coefficient. However, eddy currents resulting from the rapid switching of the bias magnetic field prevented us from making accurate measurements of the damping coefficient.

Committee: Samir Bali Dr (Advisor) Subjects: Physics

Master of Science, Miami University, 2023, Physics

This thesis discusses the study of ultracold 85Rb atoms in both molasses and optical lattices, with a focus on the implementation of a fluorescence imaging system to characterize diffusive motion of the atomic sample, and to measure temperature. Further, we show that our home-built camera and imaging system is capable of tracking sub-millisecond center-of-mass motion of the cold atom sample, by transiently applying a bias magnetic field that shifts the magneto-optical trap away from its equilibrium position. This is an important step toward our eventual goal of demonstrating a precisely controlled, directionally arbitrary ratchet in an optical lattice.

Committee: Imran Mirza (Committee Member); Carlo Samson (Committee Member); Samir Bali (Advisor) Subjects: Physics

Master of Science, Miami University, 2022, Physics

In this thesis we describe the replacement of homebuilt lasers and tapered amplifier systems used in our lab to form a 3D tetrahedral lattice with a single commercial laser system. The lattice formed by the commercial laser system is more stable, as is evidenced by significantly smaller error bars in our measurements of the vibrational frequencies using a weak probe beam aligned along the z-symmetry axis of the lattice. Further significant improvement in the agreement of the data with theory is obtained by making two important corrections in our data analysis: The lattice intensity illuminating the atoms is measured more accurately, and the error in probe alignment with the symmetry axis is better estimated.

Committee: Samir Bali (Advisor); Imran Mirza (Committee Member); E. Carlo Samson (Committee Member) Subjects: Physics

Master of Science, Miami University, 2022, Physics

Atoms confined in a dissipative three dimensional lin⊥lin optical lattice randomly diffuse in all directions, however, illumination by a weak probe beam modulates the lattice which can lead to a directed ratcheting of some atoms in a direction perpendicular to probe propagation. We determine whether this directed ratcheting, referred to as Brillouin propagation, arises from a mechanical resonance between the probe modulation frequency and oscillation frequency of the atoms confined in the wells, or, from a velocity-matching condition where the speed of the probe modulation rippling through the lattice matches the average speed of the oscillating atoms. We emphasize that a probe propagating along a symmetry axis of the lattice cannot resolve the issue as the mechanical resonance and velocity-matching conditions are satisfied simultaneously. We misaligned our probe from a lattice symmetry axis to create a situation where the condition for velocity-matching is exclusively satisfied and Brillouin propagation still occurs, thus proving the cause of this form of cold atom ratchet. The spectral signatures for Brillouin propagation in the case of an off-axis probe are investigated as a function of off-axis angle and lattice well-depth. Our data agrees well with theoretical predictions. Residual discrepancies between theory and data are analyzed.

Committee: Samir Bali (Advisor); Imran Mirza (Committee Member); Edward Samson (Committee Member) Subjects: Optics; Physics

Master of Science, Miami University, 2021, Physics

By illuminating a dissipative optical lattice with a weak frequency-scanning probe beam and detecting the probe transmission spectrum we observe a resonant enhancement in the directed propagation of cold atoms as we vary the photon scattering rate. The directed propagation is induced by probe intensities less than 1% of the total lattice intensity, and occurs perpendicular to probe propagation. Photon scattering disrupts Hamiltonian atomic motion in the reactive potentials and is thus viewed as noise, analogous to Brownian fluctuations in a thermal system. The resonant response of the system as a function of random environmental noise is a signature of stochastic resonance. We experimentally characterize the stochastic resonance as a function of system parameters such as probe intensity and lattice well-depth. A simple one dimensional model reveals how the probe-modified ground state potentials and optical pumping rates conspire to create directed atomic propagation within a randomly diffusing sample.

Committee: Samir Bali (Advisor); Imran Mirza (Committee Member); Edward Carlo Samson (Committee Member) Subjects: Physics

Master of Science, Miami University, 2020, Physics

This thesis investigates the dynamics of a sample of ultracold 85Rb atoms in a 3D tetrahedral dissipative optical lattice. By illuminating a dissipative optical lattice with a weak probe beam and measuring its transmission spectrum, we detect resonances that characterize the vibrational frequencies of the atoms, the energy spacing between light-shifted Zeeman sublevels, and directed propagation modes. We observe a resonant enhancement in the directed propagation of cold atoms as we vary the photon scattering rate. This resonant system response as a function of random environmental noise is a signature of stochastic resonance. The directed propagation is induced by probe intensities less than 1% of the lattice intensity and occurs perpendicular to probe propagation. We experimentally characterize the stochastic resonance as a function of system parameters such as probe intensity and lattice well depth. Further, we present a method for velocity-sorting cold atoms in an optical lattice by inducing velocity-specific propagation in two chosen directions.

Committee: Samir Bali (Advisor); E. Carlo Samson (Committee Member); Imran Mirza (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2020, Mathematical Sciences

This thesis describes four different projects exploring novel aspects of superconductivity in conjunction with topology and strong correlations. First, we address a fundamental question at the heart of the quest for high-temperature superconductivity: how high can the superconducting critical temperature Tc be? We derive rigorous upper bounds on Tc for two-dimensional superconductors via bounds on its stiffness to phase fluctuations. These are most useful for superconductors with strong correlations, where the usual mean-field approximations tend to fail. We calculate the maximum Tc of the recently discovered superconductor in magic-angle twisted bilayer graphene and in monolayer FeSe on SrTiO3 and find that our bound is quite close to the maximum Tc observed in both these fascinating complex systems. For a single band of electrons with parabolic dispersion in two dimensions, we show that Tc is atmost one-eight of the Fermi temperature, which places severe constraints on superconductivity in the simplest condensed matter setting, testable in experiments on ultra-cold Fermi gases. Second, we illuminate the interplay of topology and strong correlations in the normal state of an iron-based superconductor Fe(Se,Te). We show how dipole selection rules of the photoemission matrix elements can provide sharp signatures of the topological band inversion, and present data from our experimental collaborators that tests our theoretical predictions. Third, we explore the interplay of topology and superconductivity in a model which can describe a topological insulator. We find that several exotic new superconducting phases, including two new topological superconductors which reveal a generic new route to topological superconductivity in Dirac materials. Lastly, we employ a variety of analytical and numerical tools to study the emergence of superconductivity from an insulator in a simple model. Our results give insights into the question of how a superconducting instability occur (open full item for complete abstract)

Committee: Mohit Randeria (Advisor); Ilya Gruzberg (Committee Member); Thomas Lemberger (Committee Member); Yuri Kovchegov (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2019, Physics

This thesis is mainly focused on three topics: Majorana excitations in a number-conserving model, manipulation of quasi-particle excitations in quantum Hall systems, and a new machine learning algorithm to find the ground states of a general Hamiltonian. In condensed matter physics, Majorana fermions are emergent excitations which are candidates for quantum memory and topological quantum computation. The first and simplest model revealing these excitations does not conserve particle number. Its experimental realization in solid state materials is difficult and still under debate. In comparison, cold atoms provide an alternative platform to realize these exotic excitations. However, cold atoms experiments require the system to be number-conserving. Theoretically, it is not yet clear whether there is a model realizable in cold atoms that also hosts these exotic excitations. In this thesis, we investigate such a number-conserving model and show that it has the same phase diagram and very similar excitations. Although the ground state degeneracy, as one of the signature properties of the original Majorana model crucial for quantum memory, is not present when the total particle number is fixed, one can recover the degeneracy by allowing tunnelling to change the total particle number. As for the quantum Hall system, we discuss how to control quasi-hole excitations with sharp external potentials where the system has integer filling factor. The eigen wavefunctions of the quasiholes are discussed in details. Our motivation is that most discussions or experiments regarding quantum Hall systems mainly focus on transport properties, but topological quantum computation may require one to have more precise control over the quasiparticle excitations. Although the ultimate goal is to control the non-Abelian excitations predicted in fractional quantum Hall systems, our results, especially in the situation with contact interactions, pave a way to explore this problem analytical (open full item for complete abstract)

Committee: Tin-Lun Ho (Advisor); Nandini Trivedi (Committee Member); Rolando Valdes Aguilar (Committee Member); Eric Braaten (Committee Member) Subjects: Physics

Master of Science, Miami University, 2016, Physics

This thesis presents data from optical lattices using fluorescence imaging and pump-probe spectroscopy. From these experimental techniques we obtain information on the diffusion constant and vibrational frequencies of atoms confined in an optical lattice as a function of various lattice parameters. We see clear evidence of vibrational resonances which is a definite signature of optical lattices. These resonances are clearly distinguishable from Brillouin effects. We also discuss briefly our progress toward the measurement of photon correlations in light scattered by cold atoms.

Committee: Samir Bali Dr. (Advisor); James Clemens Dr. (Committee Member); Herbert Jaeger Dr. (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2014, History

This project seeks to explain why Japan developed nuclear power despite its negative experiences with nuclear weapons and fallout. It focuses on the period from the end of the American Occupation in 1952, when the Japanese regained full sovereignty, until the signing of the agreement to import a commercial British nuclear reactor in 1958. The Japanese experience with atomic bombs and radioactive fallout made Japan a seemingly unlikely candidate to develop nuclear power. These fears were renewed following the Lucky Dragon Incident when an American hydrogen bomb test showered a Japanese fishing vessel with radioactive fallout and contaminated deep water tuna throughout the Pacific. Japan, however, had ample reasons to embrace nuclear power as it: provided a potential solutions to Japan's energy crisis, while offering Japan a way to secure its place in the international community and a means of defining itself as a nation dedicated to scientific, technological, and economic development. Pro-nuclear advocates identified nuclear power as a key to the advancement of Japan, partaking in what Hiromi Mizuno termed “scientific nationalism.” Although Japanese policy makers were interested in the adopting nuclear power before the US offered to extend aid to Japan, the process of doing so was influenced by the American approach to the Cold War and was heavily informed by American efforts to maintain the support of both the government and the general public. While Japanese policy makers moved forward with their investigations of nuclear power, the United States addressed the Japanese public through a series of exhibitions as part of the Atoms for Peace program to direct the national conversation away from nuclear bomb testing. As they toured Japan, these exhibitions presented nuclear power as a suite of technologies that would greatly benefit scientific research, medicine, agriculture, industry, and transportation. Seven different national and regional newspapers cosponsored (open full item for complete abstract)

Committee: James Bartholomew (Advisor); Philip Brown (Committee Member); Christopher Reed (Committee Member) Subjects: History

Master of Science, Miami University, 2014, Physics

In this thesis we will introduce some of the theory for laser cooling and trapping and optical lattices, including the AC Stark effect (or light-shifts), polarization gradients, and Sisyphus cooling. We then present the technological advancements in our laboratory including a synopsis of home-built, inexpensive, fast imaging system and laser amplifier system which are on par with costly commercial systems and a home-built radio frequency amplifier system for driving acousto-optic modulators. We will present data that shows compelling preliminary evidence for the presence of a 1D optical lattice. We will discuss future experiments on optical ratchets.

Committee: Samir Bali PhD (Advisor); Perry Rice PhD (Committee Member); Paul Urayama PhD (Committee Member) Subjects: Physics

Master of Science, Miami University, 2014, Physics

A home built system for imaging optical lattices is presented. Our imaging system uses a repurposed astronomy camera - the complete system costs less than $5,000 while rivaling the performance of a commercially available system which costs $40-50k. The camera must have an extremely low dark current, high quantum efficiency, as well as the ability to take precisely timed millisecond exposures. Using LabVIEW a sequence of precise electronic pulses is created to control the laser beams in order to load the lattice structure with cold atoms. When running a LabVIEW VI at millisecond timescales Windows introduces inaccuracies in pulse timing. A master slave computer setup, called a real time target (RTT) is created in order to keep accuracy to the microsecond level.

Committee: Samir Bali PhD (Advisor); Perry Rice PhD (Committee Member); Herbert Jaeger PhD (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 2013, Physics

In experiments with trapped ultracold gases, atoms can be lost through inelastic scattering processes. If the atoms have a scattering length that is much larger than the range of their interactions, then the system exhibits universal behavior that does not depend on details of their interactions. Dramatic enhancements in the loss rate are observed at special negative values of the scattering length for which there is a universal molecule at threshold. In some experiments, enhancements of the loss rate have also been observed at other positive values of the scattering length. A mechanism proposed to explain this enhancement is that the losses result from many collisions of an energetic diatomic molecule created by a 3-atom collision. In this thesis, I demonstrate the failure of this mechanism as a viable explanation of the enhancement seen at positive scattering length. I present an alternative explanation for these enhancements in experiments using a Bose-Einstein condensate of atoms. They result from inelastic scattering of universal diatomic molecules in a coexisting condensate of these molecules.

Committee: Eric Braaten Ph.D. (Advisor); Yuri Kovchegov Ph.D. (Committee Member); Mohit Randeria Ph.D. (Committee Member); Stanley Durkin Ph.D. (Committee Member) Subjects: Atoms and Subatomic Particles; Condensed Matter Physics; Physics; Quantum Physics; Theoretical Physics

Master of Arts, The Ohio State University, 2009, History

This paper examines the origins of the Atoms for Peace program and its implementation in the non-Western world, with specific case studies of Brazil, India and Japan. It argues that although the program was developed as a means of starting a process nuclear disarmament and improving relations with the Soviet Union, President Eisenhower's inability to control the implementation of the program led to Atoms for Peace being used for propaganda purposes, as a means of securing nuclear raw materials and other Cold War diplomatic objectives, and to improve foreign relations with neutral and allied countries. Ultimately, bureaucratic infighting and Cold War reality made Atoms for Peace fail in its original objectives and actually increased tensions with the Soviet Union.

Committee: James Bartholomew (Advisor); Robert McMahon (Committee Member); Kevin Boyle (Committee Member) Subjects: History

Doctor of Philosophy (PhD), Ohio University, 2012, Physics and Astronomy (Arts and Sciences)

Systems, such as cold atoms and light halo nuclei, share universal features at low energies, for which details of inter-particle interactions are not essential. We study three-body physics in such systems in an effective-field-theory (EFT) framework. We will discuss universal behavior in three-body systems and higher-order effective-range corrections beyond universality. We study effective-range effects perturbatively up to the next-to-next-to-leading order (N2LO) for the case of three identical bosons. We apply this analysis to recombination features in cold atomic gases and properties of Helium trimers. Effective range corrections also play an important role in the EFT study of few-nucleon systems and halo nuclei. The ground-state of Helium-6 can be treated as a two-neutron halo with an alpha core. This bound state is generated by the resonant neutron-neutron and neutron-alpha interactions. The latter is dominated by a shallow p-wave resonance. We present a calculation of Helium-6 in an EFT approach appropriate for halo systems.

Committee: Daniel Phillips PhD (Advisor); Charlotte Elster PhD (Committee Member); Sergio Ulloa PhD (Committee Member); Gregory Van Patten PhD (Committee Member) Subjects: Physics