Vortices and Quasiparticles in Superconducting Microwave Resonators

Superconducting resonators with high quality factors are of great interest in many areas. However, the quality factor of the resonator can be weakened by many dissipation channels including trapped magnetic flux vortices and nonequilibrium quasiparticles which can significantly impact the performance of superconducting microwave resonant circuits and qubits at millikelvin temperatures. Quasiparticles result in excess loss, reducing resonator quality factors and qubit lifetimes. Vortices trapped near regions of large microwave currents also contribute excess loss. However, vortices located in current-free areas in the resonator or in the ground plane of a device can actually trap quasiparticles and lead to a reduction in the quasiparticle loss. In this thesis, we will describe experiments involving the controlled trapping of vortices for reducing quasiparticle density in the superconducting resonators. We provide a model for the simulation of reduction of nonequilibrium quasiparticles by vortices. In our experiments, quasiparticles are generated either by stray pair-breaking radiation or by direct injection using normal-insulator-superconductor (NIS)-tunnel junctions

Air Quality Implications of Future Scenarios for Oil and Natural Gas Production and Use in the Western United States

Since 2005, electricity generation in the United States has shifted from coal to increasing reliance on natural gas power plants and renewable sources while the production of oil and gas has increased to satisfy the increased demand. This shift in the energy landscape has air quality implications for local and regional air quality in the U.S., especially in the Rocky Mountain (RM) region which has abundant supplies of oil and gas and a large share of electricity generation from coal. This study aims to examine the prospective impacts of energy shifts in this region on electricity generation, emissions, ozone, and human health from 2011 to 2030. We focus on the RM region since it has several areas facing challenges to meet the National Ambient Air Quality Standard (NAAQS) for ozone. This study builds up on a previous study by McLeod et al. (2014) who applied the MARKAL (MARKet ALlocation) model and EPA&rsquo;s 9-region U.S. energy system database to investigate several future scenarios, finding the least cost means of satisfying demand for energy in each scenario and the associated annual emissions in the U.S. and the RM region out to the year 2050. We adapted four scenarios from McLeod et al.&rsquo;s study. The baseline scenario assumes a supply and prices of natural gas based on reference projections made in 2013 while the greenhouse gas (GHG) fees scenario assumes a supply of natural gas similar to the baseline scenario but applies fees to the emissions of CO2 and CH4. Two contrasting scenarios are the cheap gas scenario which assumes a high supply of natural gas at lower prices while the costly gas scenario assumes a low supply of natural gas at higher prices. We downscale emissions from electricity generation temporally and spatially to capture the effects of changes in the small-scale emissions on the local and regional air quality. The electricity generation mix is estimated using the PLEXOS dispatch model on an hourly basis for a one-year period. The estimated generation from coal and natural gas power plants in each scenario is combined with unit specific emissions rates to determine the future emissions from power plants. Annual oil and gas production in the RM region are downscaled to the basin level to determine basin specific scaling factors used to estimate future emissions scenarios from oil and gas production. The estimated emissions from power plants and oil and gas production as well as emissions from other energy sectors are processed with the SMOKE software package and then incorporated into the CAMx chemistry and transport model to determine the change in ozone associated with changes in emissions in the different scenarios. A health benefits analysis tool, BenMAP-CE, is used with the ozone modeling results to determine the human health impacts and their monetary value associated with the change in ozone. We find that electricity production in the western U.S. from coal and natural gas increases from 2011 to 2030 along with generation from renewable energy as electricity demand increases from population growth. Contrary, to the trend in generation, NOx emissions from electricity production decrease by 33% over the same period as a result of retirement of old inefficient coal-fired plants, power plant refueling, and emissions control application. Within the western U.S, electricity generation and emissions vary by state and time of the year. Oil and gas production increases from 2011 to 2030 corresponding to increased demand, hence NOx and VOC emissions from oil and gas production increase by 5% and 58%, respectively, despite the emissions reductions from regulations imposed on the oil and gas sector. The net tradeoffs in these emissions trends lead to reductions in the summer MDA8 ozone as high as 8 ppb from 2011 to 2030, especially downwind of power plants and oil and gas basins in the 4 km CAMx domain. However, elevated ozone persists in urban areas such as Denver and Salt Lake City during peak time periods. The reduction in ozone from 2011 to 2030 is estimated to result in 303 to 360 reductions in premature deaths per year in the 4 km CAMx domain, in addition to reductions of morbidities associated with ozone. Between scenarios, electricity generation from natural gas displaces some coal generation in the cheap gas scenario compared to the 2030 baseline scenario, while renewable energy capacity expansion, particularly wind energy, displaces generation from coal and natural gas in the costly gas and the GHG fees scenarios. A similar trend is observed in the oil and gas production with production increasing in the cheap gas scenario and decreasing in the costly gas and the GHG fees scenarios. In the western U.S, total annual NOx emissions from electricity generation decrease in all scenarios from the baseline scenario by 7% to 40% while NOx emissions from oil and gas production increase 27% in the cheap gas scenario and decrease 21% and 16% in the costly gas and the GHG fees scenarios, respectively. Changes in the annual total VOC emissions are a 37% increase with the cheap gas scenario and reductions of 25% and 22% in the costly gas and GHG fees scenarios, respectively. For the 4 km CAMx domain, these trends in emissions lead to a modest overall spring and summer MDA8 ozone increase from the baseline to the cheap gas scenario with a maximum increase of 1.5 ppb. In contrast, ozone decreases from the baseline to the GHG fees scenario, with a maximum decrease in MDA8 ozone of 2 ppb. Correspondingly, health effects benefits are estimated from the GHG fees scenario with premature deaths decreasing by 27 to 32 per year compared to the 2030 baseline. The cheap gas scenario offsets some of the health benefits gained in the 2030 baseline scenario.</p

Engineering the Level Structure of a Giant Artificial Atom in Waveguide Quantum Electrodynamics

Engineering light-matter interactions at the quantum level has been central to the pursuit of quantum optics for decades. Traditionally, this has been done by coupling emitters, typically natural atoms and ions, to quantized electromagnetic fields in optical and microwave cavities. In these systems, the emitter is approximated as an idealized dipole, as its physical size is orders of magnitude smaller than the wavelength of light. Recently, artificial atoms made from superconducting circuits have enabled new frontiers in light-matter coupling, including the study of "giant" atoms which cannot be approximated as simple dipoles. Here, we explore a new implementation of a giant artificial atom, formed from a transmon qubit coupled to propagating microwaves at multiple points along an open transmission line. The nature of this coupling allows the qubit radiation field to interfere with itself leading to some striking giant-atom effects. For instance, we observe strong frequency-dependent couplings of the qubit energy levels to the electromagnetic modes of the transmission line. Combined with the ability to in situ tune the qubit energy levels, we show that we can modify the relative coupling rates of multiple qubit transitions by more than an order of magnitude. By doing so, we engineer a metastable excited state, allowing us to operate the giant transmon as an effective lambda system where we clearly demonstrate electromagnetically induced transparency.Comment: 12 pages, 8 figure

Observation of Three-Photon Spontaneous Parametric Down-Conversion in a Superconducting Parametric Cavity

Spontaneous parametric down-conversion (SPDC) has been a key enabling technology in exploring quantum phenomena and their applications for decades. For instance, traditional SPDC, which splits a high-energy pump photon into two lower-energy photons, is a common way to produce entangled photon pairs. Since the early realizations of SPDC, researchers have thought to generalize it to higher order, e.g., to produce entangled photon triplets. However, directly generating photon triplets through a single SPDC process has remained elusive. Here, using a flux-pumped superconducting parametric cavity, we demonstrate direct three-photon SPDC, with photon triplets generated in a single cavity mode or split between multiple modes. With strong pumping, the states can be quite bright, with flux densities exceeding 60 photons per second per hertz. The observed states are strongly non-Gaussian, which has important implications for potential applications. In the single-mode case, we observe a triangular star-shaped distribution of quadrature voltages, indicative of the long-predicted "star state." The observed state shows strong third-order correlations, as expected for a state generated by a cubic Hamiltonian. By pumping at the sum frequency of multiple modes, we observe strong three-body correlations between multiple modes, strikingly, in the absence of second-order correlations. We further analyze the third-order correlations under mode transformations by the symplectic symmetry group, showing that the observed transformation properties serve to "fingerprint" the specific cubic Hamiltonian that generates them. The observed non-Gaussian, third-order correlations represent an important step forward in quantum optics and may have a strong impact on quantum communication with microwave fields as well as continuous-variable quantum computation

Investigation of the impact of crystal sizes of Metal-Organic Frameworks on their heterogeneous catalytic activity for oxidation reactions

Metal-organic frameworks (MOFs) are porous crystalline materials comprised of metal nodes spanned by organic linkers with desirable properties for catalysis, such as high metal content and surface areas. MOFs crystals grow through self-assembly of their key components. Coordination modulation offers an efficient way to control crystal growth and was utilized in this work for the synthesis of HKUST-1 (Hong Kong University of Science and Technology)- a framework that consists of copper ions and 1,3,5-benzene tricarboxylic acid (BTC)-to scale the micron to nanometer regimes. By varying equivalents of benzoic and dodecanoic acid, HKUST-1 crystals with sizes ranging from 220 nm to 1.5 μm were synthesized. The diffusion of reactants to the active surface area within porous catalyst particles is a crucial step in liquid-phase organic oxidation reactions. Using reaction-diffusion theory, as-synthesized crystal sizes were then used to model diffusion and reaction within HKUST-1 crystals. The transport of reactants to the active surface areas by diffusion limited impaired the conversion of cyclooctene when sizes were larger than 300 nm

Investigation of the impact of crystal sizes of Metal-Organic Frameworks on their heterogeneous catalytic activity for oxidation reactions

Metal-organic frameworks (MOFs) are porous crystalline materials comprised of metal nodes spanned by organic linkers with desirable properties for catalysis, such as high metal content and surface areas. MOFs crystals grow through self-assembly of their key components. Coordination modulation offers an efficient way to control crystal growth and was utilized in this work for the synthesis of HKUST-1 (Hong Kong University of Science and Technology)- a framework that consists of copper ions and 1,3,5-benzene tricarboxylic acid (BTC)-to scale the micron to nanometer regimes. By varying equivalents of benzoic and dodecanoic acid, HKUST-1 crystals with sizes ranging from 220 nm to 1.5 μm were synthesized. The diffusion of reactants to the active surface area within porous catalyst particles is a crucial step in liquid-phase organic oxidation reactions. Using reaction-diffusion theory, as-synthesized crystal sizes were then used to model diffusion and reaction within HKUST-1 crystals. The transport of reactants to the active surface areas by diffusion limited impaired the conversion of cyclooctene when sizes were larger than 300 nm

Investigation of the impact of crystal sizes of Metal-Organic Frameworks on their heterogeneous catalytic activity for oxidation reactions

Metal-organic frameworks (MOFs) are porous crystalline materials comprised of metal nodes spanned by organic linkers with desirable properties for catalysis, such as high metal content and surface areas. MOFs crystals grow through self-assembly of their key components. Coordination modulation offers an efficient way to control crystal growth and was utilized in this work for the synthesis of HKUST-1 (Hong Kong University of Science and Technology)- a framework that consists of copper ions and 1,3,5-benzene tricarboxylic acid (BTC)-to scale the micron to nanometer regimes. By varying equivalents of benzoic and dodecanoic acid, HKUST-1 crystals with sizes ranging from 220 nm to 1.5 μm were synthesized. The diffusion of reactants to the active surface area within porous catalyst particles is a crucial step in liquid-phase organic oxidation reactions. Using reaction-diffusion theory, as-synthesized crystal sizes were then used to model diffusion and reaction within HKUST-1 crystals. The transport of reactants to the active surface areas by diffusion limited impaired the conversion of cyclooctene when sizes were larger than 300 nm

Observation of Three-Photon Spontaneous Parametric Down-Conversion in a Superconducting Parametric Cavity

Spontaneous parametric down-conversion (SPDC) has been a key enabling technology in exploring quantum phenomena and their applications for decades. For instance, traditional SPDC, which splits a high-energy pump photon into two lower-energy photons, is a common way to produce entangled photon pairs. Since the early realizations of SPDC, researchers have thought to generalize it to higher order, e.g., to produce entangled photon triplets. However, directly generating photon triplets through a single SPDC process has remained elusive. Here, using a flux-pumped superconducting parametric cavity, we demonstrate direct three-photon SPDC, with photon triplets generated in a single cavity mode or split between multiple modes. With strong pumping, the states can be quite bright, with flux densities exceeding 60 photons per second per hertz. The observed states are strongly non-Gaussian, which has important implications for potential applications. In the single-mode case, we observe a triangular star-shaped distribution of quadrature voltages, indicative of the long-predicted “star state.” The observed state shows strong third-order correlations, as expected for a state generated by a cubic Hamiltonian. By pumping at the sum frequency of multiple modes, we observe strong three-body correlations between multiple modes, strikingly, in the absence of second-order correlations. We further analyze the third-order correlations under mode transformations by the symplectic symmetry group, showing that the observed transformation properties serve to “fingerprint” the specific cubic Hamiltonian that generates them. The observed non-Gaussian, third-order correlations represent an important step forward in quantum optics and may have a strong impact on quantum communication with microwave fields as well as continuous-variable quantum computation