Abstract: In recent years, neutral atom tweezer arrays have emerged as a promising platform for quantum computing. Among various atomic species, alkaline-earth(-like) atoms—particularly ytterbium—offer unique advantages arising from their rich internal structure. In this talk, I will present progress from my PhD work, demonstrating how these features can be harnessed to build a useful quantum computer in the future. This includes the generation of high-fidelity entanglement between metastable-state qubits and the implementation of mid-circuit erasure conversion for quantum error correction. I will also discuss our ongoing efforts to further improve two-qubit gate fidelity by leveraging detailed numerical models tailored to the ytterbium platform.

A surprising discovery has been compact systems of Earth to super- Earth-sized planets. While compact systems are common, their origin is debated. A prevalent assumption is that compact systems formed after the infall of gas and solids to the circumstellar disk ended. However, observational evidence suggests accretion may commence earlier. We propose that compact systems are surviving remnants of planet accretion during the end stages of infall. In disk regions undergoing infall, a planet's mass is regulated by a balance between growth due to the supply of solids, and inward gas-driven orbital migration that becomes faster as the planet grows, replicating the intra-system planetary-size-similarly. We show that infall-produced planets can survive until the gas disk disperses and migration ends, and that the mass of surviving compact systems is regulated to between a few x 10^-5 and 10^-4 stellar mass. This provides an explanation for the remarkably similar mass ratios of known compact systems.

The quantum 2.0 revolution is well underway, with a tantalizing future just over the horizon wherein computing, networking, sensing, and even time-keeping will be unimaginably more capable than they are today. The promise of this future hinges on the ability to control, entangle, and measure both individual qubits and large systems of them. Many of the most promising physical qubit systems being developed for these purposes are atomic in nature, i.e. trapped neutral atoms, trapped ions, and artificial atoms in crystals. These atomic qubits interact almost exclusively with visible or even UV photons, requiring incredibly precise phase, frequency, and amplitude conditioning of and modulation of those photons to control them. While these systems have advanced by leaps and bounds over the last decade by focusing on small-scale implementations with a few to a few thousand qubits using “tabletop” optical controls, all of them are now bottlenecked by the inability to scale these controls to the qubit counts required for true scientific, technological, and societal utility, which will require several orders of magnitude more qubits with no degradation in performance.

In this talk, I will describe my group’s past, present, and future efforts to clear this bottleneck by hijacking the most scalable manufacturing processes known to man—those used to manufacture complimentary metal-oxide semiconductor (CMOS) electronic integrated circuits—to make very large-scale optical control circuits. To do this, we have developed a novel photonic integrated circuit (PIC) architecture that uses integrated piezoelectric force actuators to deform dielectric waveguides made of common CMOS insulators: silicon nitride, silicon dioxide, and aluminum oxide. I will show that this piezo-optomechanical PIC architecture provides electronic control of all the necessary degrees of freedom for photons across the entire visible spectrum and far enough into the ultraviolet to address the most important qubit species. Critically, the PIC platform has high modulation bandwidth, works from room temperature to cryogenic temperatures, handles optical power up to (at least) several watts, and has low power dissipation, self-heating, and cross-talk, paving the way towards utility scale quantum information processing with atomic qubits.

Abstract: A new zoo consisting of dozens of heavy subatomic particles that contain more than three quarks and antiquarks have been discovered beginning in 2003.  Although they must be described by the fundamental quantum field theory QCD, the pattern of these exotic heavy hadrons remained unexplained for more than 20 years.  I will present a simple proposal for the pattern based on the Born-Oppenheimer approximation for QCD.  There are simple calculations in lattice QCD that would corroborate the pattern.  The quantitative description of these exotic heavy hadrons requires the diabatic representation of the Born-Oppenheimer approximation, which has led to dramatic advances in atomic and molecular physics in recent decades.

Atomic electron tomography (AET) enables the determination of 3D atomic structures by acquiring a sequence of 2D TEM projection measurements of a particle and then computationally solving for its underlying 3D representation. AET is a challenging and labor-intensive experiment! In this talk, we offer two computational methods to alleviate these challenges and make the reconstruction procedure more robust.

First, we describe a method that solves directly for the locations and properties of individual atoms from projection measurements. This is in contrast to classical tomography algorithms that first solve for a volume and then extract the atomic structure. We parameterize a particle as a collection of atoms each represented by a Gaussian. We show that this parameterization imparts a strong prior on the reconstruction that avoids physically implausible artifacts often present in volumetric reconstructions due to noise and missing wedge effects. These reconstruction improvements further translate to higher fidelity atomic structure identification.

Second, we tackle the problem of carbon contamination: over the time it takes to capture the tomographic projection series, amorphous carbon often accumulates on the sample surface, making it difficult to reconstruct the underlying static sample and causing laboriously collected datasets to be discarded. We use implicit neural representations, which compactly represent large 3D+time data cubes and impose flexible space-time priors, to directly model and solve for the 3D temporal dynamics of the sample  This allows us to computationally remove the contamination and recover an uncorrupted reconstruction of the static sample of interest. 

NASA science missions are often complex systems of systems, involving various stakeholders, including the United States’ Congress. To ensure a clear and concise communication of expectations, requirements, and constraints, NASA has adopted the Science Traceability Matrix (STM). STM provides a logical flow from the decadal survey to science goals and objectives, mission and instrument requirements, and data products. STM serves as a summary of what science will be achieved and how it will be achieved, with a clear definition of what mission success will look like. In this seminar, I will present the STM from the Parker Solar Probe (PSP), including requirements relating to the plasma instrument for which I am a co-investigator. I will describe how our team used the STM to map the mission’s top-level requirements to mission success criteria and helped to eliminate any single point of failure that could end the mission prematurely. I will then present my own research on magnetic switchbacks in the PSP magnetic and plasma observations and their role in solar wind acceleration and heating. I will conclude the seminar by discussing how my research on the temporal evolution of switchbacks in the solar wind led to a new STM, and helped to chart a multidisciplinary path to designing a ground-breaking science mission concept, titled Space Weather Investigation Frontier (SWIFT), with the potential to improve space weather forecasting lead times by up to 40%.

Linear spectroscopy is used to learn about transitions from the ground states of systems. Nonlinear spectroscopies, such as transient absorption (TA) spectroscopy, first excite the system and then probe after some time delay, giving dynamical information about excited states and spectral information about their excitations. If the pump pulses are strong enough, then some molecules are excited multiple times, and the signal has contributions from singly excited molecules mixed with those from multiply excited molecules. Such mixed signals are hard to interpret, so TA spectra are often acquired with a sufficiently weak pump pulse that the higher-order contributions can be neglected. But the signal-to-noise ratio becomes worse when the pump is weak.

I will describe a general method to systematically separate spectroscopic orders of response by acquiring spectra with multiple pump-pulse energies, with applications in many forms of spectroscopy. This method allows acquisitions with increased pump intensities that improve signal-to-noise while systematically removing contaminations from higher-order processes. High-order responses have not previously been separable, and I will give examples of the spectral and dynamical information that they can contain, from exciton-exciton-annihilation kinetics to revealing masked signals in congested spectra. I will show experimental demonstrations from TA and two-dimensional electronic spectroscopy. I will show how to choose the pulse intensities to give the best extractions of response orders, given the noise present.

TBA

From planting crops to making trains run efficiently, clocks have been an important tool throughout most of human history. Atomic clocks, based on quantum-mechanically-defined transitions in atoms, are currently the most accurate realizations of the second and underlie important technologies such as the global positioning system (GPS) and high-speed communications. This lecture will describe how atomic clocks work and their history, with a focus on compact clocks and the applications in which they are used.

The Department of Biochemistry invites professors and scientists from other universities and institutes to present seminars at the University of Colorado Boulder throughout the academic year. These seminars provide an opportunity for faculty and students to learn about exciting current research.

TBA

Solar and stellar flares are explosive phenomena in which magnetic energy stored around starspots is suddenly released through magnetic reconnection. The radiation emitted during flares covers a broad range of wavelengths from radio to X-rays, each tracing different aspects of the flare process. In X-rays, the emission arises from hot thermal plasma heated by nonthermal electrons that travel upward from the chromosphere into the corona.

RS CVn-type binaries and protostars exhibit giant flares that are several orders of magnitude more energetic than those on the Sun, and it remains unclear whether their underlying physical processes are fundamentally the same as in solar flares. Furthermore, the impact of high-energy radiation from flares on exoplanetary environments has attracted increasing attention. In particular, X-ray emission from protostars has recently drawn significant interest from the star and planet formation community in the context of X-ray–driven chemistry, as it may strongly affect the surrounding protoplanetary disks.

In X-ray observations of stellar flares, NICER — with its combination of large effective area and high observational agility — has played a key role. Furthermore, XRISM, which has an order of magnitude higher energy resolution than NICER, was launched in 2023. In this talk, I focus on the Fe K-shell emission lines in X-ray, which are covered by both of these satellites, and introduce the physics of stellar flares and its effect on exoplanetary environments that can be inferred from their line intensities and structures.

The Department of Biochemistry invites professors and scientists from other universities and institutes to present seminars at the University of Colorado Boulder throughout the academic year. These seminars provide an opportunity for faculty and students to learn about exciting current research.