Eric Sembrat's Test Bonanza

Title: Tilted Planets: Exciting Exoplanetary Obliquities via Spin-Orbit Resonances
Abstract: The obliquity of a planet, the tilt between its spin and orbital axes, reflects the evolutionary history of the planet. In our own Solar System, the 98 degree obliquity of Uranus is hypothesized to be the result of giant impacts during its formation, and the 4 and 26 degree obliquities of Jupiter and Saturn are thought to be the result of spin-orbit resonances due to the gravitational influence of Uranus and Neptune respectively. While there have been few direct constraints on the obliquities of sub-stellar-mass objects beyond our Solar System, there are prospects for better constraints on exoplanetary obliquities in the coming years. Such measurements are important for informing the surface conditions and potential habitability of exoplanets. In this talk, I will describe some mechanisms by which exoplanetary obliquities can be excited due to the rich dynamics resulting from the interaction between tides and spin-orbit resonances. I will use these results to assess the prospects of substantially oblique exoplanets in a few important systems of interest. I will also discuss my results on spin evolution in dynamically-formed binary black hole mergers, which are similar in many ways to the planetary dynamics.

Abstract: Trapped ion systems are a strong candidate for quantum information processing due to the long lifetimes of their internal electronic states, which can be treated as two-level quantum system called a qubit. Trapped ions and atoms are unique among other physical quantum information platforms because their position is not fixed, and they can be spatially manipulated with electric fields. This characteristic is widely used in logic-passive operations such as ion loading and transport between different regions in a trap, but it is not often actively incorporated into qubit manipulations. This thesis describes research into techniques that take advantage of transport operations to produce one- and two-qubit operations on two co-trapped calcium-40 ions. The first technique involves single-ion addressing achieved via sequences of laser pulses and modulations of the confining electric field potential; I describe my contributions to lowering the motional heating during the potential modulations and applying the single-ion addressing technique to perform quantum process tomography. The second transport-enhanced technique is the first demonstration of a two-qubit entangling gate performed on ions during transport; I outline the experimental methods used to characterize and tailor the transport to achieve entanglement during the interaction.

Abstract: Ultra-cold fermions loaded in optical lattices have become ideal systems to study related electronic phase diagrams and transport properties, because they provide a clean and well controlled playground to change various lattice parameters and external fields at the turn of a knob. It is now possible to create artificial magnetic fields in optical lattices that mimic electronic materials exhibiting integer and fractional quantum Hall effects. The synthetic magnetic flux values created in optical lattices are sufficiently large to allow for the experimental exploration of the intricacies of Harper’s model and the Hofstadter butterfly, as well as the experimental determination of Chern numbers. For ultracold fermions in optical lattices, artificial magnetic fields enable studies of topological insulators that break time-reversal symmetry, such as quantum Hall systems, while artificial spin-orbit fields allow for studies of topological insulators that do not break time-reversal symmetry, such as quantum spin Hall systems. Both types of topological insulators are characterized by Berry curvatures and Chern numbers, which have been measured experimentally using time-of-flight techniques, inspired by theoretical proposals, and using dynamics of the center of mass of the atomic cloud, also motivated by theoretical work. However, studies of ultracold fermions may go beyond the quantum simulation of spin-1/2 topological insulators under typical condensed matter conditions, because artificial magnetic, spin-orbit, and Zeeman fields may be adjusted independently. The thesis develop the topological properties and discuss the quantum Hall responses of SU(N) fermions in two-dimensional lattices, when artificial magnetic flux and color-orbit coupling are present.

Abstract

Periodic networks on the verge of mechanical instability, called Maxwell lattices, are known to exhibit zero-frequency modes localized to their boundary. Importantly, these zero modes are protected against disorder by their reciprocal-space topology so that the edge-selectivity is referred to as the topological polarization of the lattice. Here, we investigate a class of mechanical bilayers as a model system for designing topologically protected edge modes that couple in-plane extensional modes to out-of-plane flexural modes, a paradigm that we refer to as omnimodal polarization. We develop a design principle that utilizes mirror-symmetric kagome bilayers, which inherit the topological polarization of their constitutive planar monolayers. The coupling between these layers results in the omnimodal polarization of the bilayer, whereby extensional and flexural edge modes localize on the same edge, by antisymmetric actuation of the in-plane edge modes. We expand upon these theoretical results by fabricating a mirror-symmetric kagome bilayer with elastic beams via additive manufacturing. We show that the frequency of the edge modes scale with the bending stiffness of the beams until they hybridize with the bulk modes and delocalize. Finally, we confirm this simultaneous edge- and frequency-selectivity via finite element analysis and laser-vibrometry experiments.

Abstract: Biological systems can use seemingly simple rhythmic body and/or limb undulations to traverse their natural terrains. We are particularly interested in the regime of locomotion in highly damped environments, which we refer to as geometric locomotion. In geometric locomotion, net translation is generated from properly coordinated self-deformation to counter drag forces. The scope of geometric locomotion is broad across scales with diverse morphologies. For example, at the macroscopic scale, legged animals such as fire salamanders (Salamandra salamandra), display high maneuverability by properly coordinating their body bending and leg movements. At the microscopic scale, nematode worms, such as C. elegans, can manipulate body undulation patterns to facilitate effective locomotion in diverse environments. These movements often require proper coordination of animal limbs and body; more importantly, such coordination patterns are environment dependent. In robotic locomotion, however, the state-of-the-art gait design and feedback control algorithms are computationally costly and typically not transferable across platforms (body-morphologies and environments), thus limiting the versatility and performance capabilities of engineering systems. While it is challenging to directly replicate the success in biological systems to robotic systems, the study of biological locomotors can establish simple locomotion models and principles to guide the robotics control process. The overarching goal of this thesis is to connect the observations in biological systems to the optimization problems in robotics applications. In the last 30 years, a framework called “geometric mechanics” has been developed as a general scheme to link locomotor performance to the patterns of “self-deformation”. This geometric approach replaces laborious calculation with illustrative diagrams. Unfortunately, this geometric approach was limited to low degree-of-freedom systems while assuming idealized contact models with the environment. This thesis develops and advances the geometric mechanics framework to overcome both of these limitations; and thereby throws insights into understanding a variety of animal behaviors as well as controlling robots, from short-limb elongate quadrupeds to body-undulatory multi-legged centipedes.

Abstract: Narrow linewidth atomic transitions provide opportunities for the development of various quantum technologies. Thulium has an unfulfilled 4f orbital with an electronic configuration similar to Yb3+ which is used in several solid-state optical applications. The fine structure of thulium atom is split into a ground state 2F7/2 and an excited state 2F5/2 which is at an energy of 8771 cm-1 above the ground state. Because the 4f orbital remains submerged underneath the fully filled 5s, 5p and 6s orbitals lying close to the nucleus, the magnetic dipole transition at 1140 nm has very narrow linewidth and in previous works, it was found that the transition was not broadened significantly when trapped in liquid and solid helium. Motivated by this fact that the narrow linewidth transitions observed in thulium coming from the inner shell transitions might have possible applications in building atomic sensors, thulium atoms are studied by trapping them in the solid crystals of argon and neon at cryogenic temperatures. An experimental setup is built to trap the thulium atoms in the “matrix” of argon and neon, and the samples are prepared on a sapphire substrate and on the tip of a cold multimode fiber. With a home-built high-resolution spectrometer for emission spectroscopy and the method of laser absorption spectroscopy, we demonstrated that the magnetic dipole transition is in fact split into multiple components because of the crystal field from argon/neon. In addition to that, we found that the thulium atoms are trapped in multiple trapping sites which are reproducible giving emissions at different wavelengths. We found there was homogeneously broadened lines in thulium without any significant inhomogeneous broadening. The experimental setup, sample preparation methods, and results from high-resolution spectroscopy to reveal the internal structure of the thulium atoms will be discussed.

Abstract: "DeepCore, a densely instrumented sub-detector of IceCube, extends IceCube’s energy reaches down to about 10 GeV, enabling the search for astrophysical transient neutrino sources. I aim to utilize a newly developed event selection and dataset for both a triggered and an untriggered all-sky search for potential astrophysical neutrino origins.

For the first analysis presented in this thesis, gamma-ray bursts (GRBs) are proposed as neutrinos emitters. Despite predictions for multi-GeV neutrino emissions from collisions of drifting neutrons in sub-photospheric GRB emissions or particle acceleration in internal shocks, the energy range studied in this study had received little attention. I present the results of a search for tens of GeV neutrinos in coincidence with GRBs using IceCube-DeepCore. This analysis was conducted on eight years of IceCube-DeepCore data and in coincidence with 2,268 GRBs. I first look for correlations between neutrino events and GRBs using six overlapping time windows centered on the prompt phase of each GRB. These time windows range from ±5 s to ±250 s. Individual p-values are combined using a binomial test to look for a potential subgroup of GRBs that could be neutrino sources by identifying an excess of GRBs with p-values less than a certain threshold. There is no evidence of neutrino emission in either search. Fermi GBM bn140807500 is the most significant individual burst, with a p-value of 0.01 corrected for testing 2268 GRBs. The binomial test does not identify any additional GRBs and yields a p-value of 0.65 when all thresholds are considered. The ongoing IceCube Upgrade is expected to improve angular resolution and energy reconstruction of events, improving the sensitivity of future studies.

Astrophysical neutrino sources that cannot be observed using multi-wavelength photons, such as choked-GRBs, are candidate targets for the second untriggered analysis shown in this thesis. I expand the previous DeepCore transient half-sky search to an all-sky time-dependent search using the same newly developed dataset used in the above analysis, focusing only on short-lived sources with a flare duration of 102 - 105 seconds. This thesis shows all-sky sensitivities to potential neutrino transients with energies ranging from 10 GeV to 300 GeV. I demonstrate that DeepCore can be used to conduct reliable all-sky searches for short-lived astrophysical sources. IceCube-DeepCore is expected to be used for all-sky searches on larger timescale sources with future extensions to the standard likelihood method explored in this thesis."

Abstract: Despite a long and rich history of scientific investigation, fluid turbulence remains one of the most challenging problems in science and engineering. One of the key outstanding questions concerns the role of coherent structures that describe frequently observed patterns embedded in turbulence. It has been suggested, but not proven, that coherent structures correspond to unstable, recurrent solutions of the governing equations of fluid dynamics. In this talk, I will present the first experimental evidence that three-dimensional turbulent flow mimics the spatial and temporal structure of multiple such solutions episodically but repeatedly. These results provide compelling evidence that coherent structures, grounded in the governing equations, can be harnessed to predict how turbulent flows evolve.