Quantum electrodynamics of a superconductor-insulator phase transition

A chain of Josephson junctions implements one of the simplest many-body models undergoing a superconductor-insulator (SI) quantum phase transition between states with zero and infinite resistance. Apart from zero resistance, the superconducting state is necessarily accompanied by a sound-like mode due to collective oscillations of the phase of the complex-valued order parameter. Exciting this phase mode results in transverse photons propagating along the chain. Surprisingly little is known about the fate of this mode upon entering the insulating state, where the order parameter's amplitude remains non-zero, but the phase ordering is "melted" by quantum fluctuations. Here we report momentum-resolved radio-frequency spectroscopy of collective modes in nanofabricated chains of Al/AlOx/Al tunnel junctions. We find that the phase mode survives remarkably far into the insulating regime, such that $\textrm{M}\Omega$-resistance chains carry $\textrm{GHz}$-frequency alternating currents as nearly ideal superconductors. The insulator reveals itself through broadening and random frequency shifts of collective mode resonances, originated from intrinsic interactions. By pushing the chain parameters deeper into the insulating state, we achieved propagation with the speed of light down to $8\times 10^5~\textrm{m/s}$ and the wave impedance up to $23~\textrm{k}\Omega$. The latter quantity exceeds the predicted critical impedance by an order of magnitude, which opens the problem of quantum electrodynamics of a Bose glass insulator for both theory and experiment. Notably, the effective fine structure constant of such a 1D vacuum exceeds a unity, promising transformative applications to quantum science and technology.Comment: Revised with new experiments and theor

Protecting a superconducting qubit from energy decay by selection rule engineering

Quantum control of atomic systems is largely enabled by the rich structure of selection rules in the spectra of most real atoms. Their macroscopic superconducting counterparts have been lacking this feature, being limited to a single transition type with a large dipole. Here we report a superconducting artificial atom with tunable transition dipoles, designed such that its forbidden (qubit) transition can dispersively interact with microwave photons due to the virtual excitations of allowed transitions. Owing to this effect, we have demonstrated an in-situ tuning of qubit's energy decay lifetime by over two orders of magnitude, exceeding a value of $2~\textrm{ms}$, while keeping the transition frequency fixed around $3.5~\textrm{GHz}

Indoors is fine, but outdoors is even better. Qualitative studies of outdoor education.

Bacheloroppgave, grunnskolelærerutdanning, 2018.Norsk: I denne bacheloroppgave tar jeg for meg undersøkelse av hvordan uteskole påvirker interessen for matematikk. Forskningen er basert på intervju av 6 elever som ble gjennomført i etterkant av uteskoledagen. I oppgaven ser jeg generelt på uteskole og ser også på uteskolematematikk med geometri som tema. Det jeg kom frem til viser at selv om forholdet til oppgaver og interesse for matematikk varierte, har elevene vist et positivt forhold til uteskole og har gitt uttrykk for at de likte oppgavene de hadde ute. Det at de opplever undervisningen som noe interessant og morsomt, vil motivasjonen deres øke og de vil yte mer. Interessen for matematikk gir et godt utgangspunkt for læring.Engelsk: This bachelor thesis is a research about how does outdoor education affect interest for mathematics. Research is based on interview with 6 pupils and was completed few days after the class had their outdoor education day. The study focused outdoor education generally as well as about mathematics outside the classroom, where the topic was geometry. The results of the study were that even though the levels in math were different, the informants were positive to outdoor education. It revealed that the pupils liked to have education outside the classroom. Pupils expressed that this kind of education is interesting and funny, which will affect their motivation, effort and determination. To be interested in mathematics gives a god foundation to build knowledge on

Atomistic and Cellular Analysis of Start Phosphatidylinositol Transfer Proteins in the Context of the Phospholipid Extraction Mechanism and Phosphoinositide Signaling in the Parasite Toxoplasma

Phosphatidylinositol transfer proteins (PITPs) are essential regulators of the interface between phosphoinositide (PIP) signaling and membrane trafficking in eukaryotic cells. Genetic derangement of PITPs in multicellular organisms results in pathologies such as neurodegeneration, metabolic diseases, and vision and neurosensory defects. How PITPs sense multiple metabolic inputs to specify a membrane signaling event is key to our understanding of these pathologies and of PIP networks in general. To that end, we describe a novel multi-domain PITP of the START structural family: PITP Multidomain Protein (PIMP) is encoded by the eukaryotic parasite Toxoplasma, and associated with specialized parasite organelles called dense granules. Dense granules are secretory organelles that traffic Toxoplasma proteins during parasite infection of the mammalian host. PIMP links a PITP domain to an oxysterol binding protein (OSBP) domain. PITP and OSBP orthologs in other eukaryotes are expressed as separate proteins known to antagonize each other in specific PIP signaling pathways. We report that PIMP is a bona fide PITP in vivo and in vitro, and its binding and extraction of phosphatidylinositol (PtdIns) from membranes is required for this function. Furthermore, PIMP binds phosphatidylcholine as a counter-ligand to PtdIns, and senses specific higher order PIPs, PtdIns4P and PtdIns(4,5)P2 through a conserved plekstrin homology (PH) domain. We describe how Toxoplasma codes its secretory system with unique PtdIns4P pools, and define PIMP as a sensor of PIP pools on dense granules. Thus PIMP is a dense granule protein that represents a novel platform for the integration of multiple metabolic inputs with PtdIns4P signaling. The mechanism by which the PIMP PITP domain, or indeed any START PITP, extracts phospholipids from bilayers is unknown. We performed molecular dynamics simulations using the mammalian PITPα as a START PITP model. We report atomistic detail of the trajectory of phospholipids into the START PITP binding pocket. Overall, this work analyzes START PITP function on the atomistic and cellular levels, and offers possible explanations for how these proteins organize specific PIP signaling events.Doctor of Philosoph

An analysis of Atlantic Water in the Arctic Ocean using the Arctic Subpolar Gyre State Estimate and observations

Submitted in partial fulfillment of the requirements for the degree of Master of Science in Physical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2020.The Atlantic Water (AW) Layer in the Arctic Subpolar gyre sTate Estimate (ASTE), a regional, medium-resolution coupled ocean-sea ice state estimate, is analyzed for the first time using bounding isopycnals. A surge of AW, marked by rapid increases in mean AW Layer potential temperature and AW Layer thickness, begins two years into the state estimate (2004) and traverses the Arctic Ocean along boundary current pathways at approximately 2 cm/s. The surge also alters AW flow direction and speed including a significant reversal in flow direction along the Lomonosov Ridge. The surge results in a new quasi-steady AW flow from 2010 through the end of the state estimate period in 2017. The time-mean AW circulation during this time period indicates a significant amount of AW spreads over the Lomonosov Ridge rather than directly returning along the ridge to Fram Strait. A three-layer depiction of ASTE’s overturning circulation within the AO indicates AW is converted to colder, fresher Surface Layer water at a faster rate than is transformed to Bottom Water (1.2 Sv vs. 0.4 Sv). Observed AW properties compared to ASTE output indicate increasing misfit during the simulated period with ASTE’s AW Layer generally being warmer and thicker than in observations.This research was funded via the United States Navy’s Civilian Institution Program with the MIT/WHOI Joint Program (JP). The thesis supervisor’s participation in this project was supported by National Science Foundation-Grant #PLR-1603660 and by Office of Naval Research-Grant #N000141612381. This project, specifically ASTE developed by Dr. An T. Nguyen, is also supported by National Science Foundation-Grant #PLR-1603903

An analysis of Atlantic water in the Arctic Ocean using the Arctic subpolar gyre state estimate and observations

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Grabon, J. S., Toole, J. M., Nguyen, A. T., & Krishfield, R. A. An analysis of Atlantic water in the Arctic Ocean using the Arctic subpolar gyre state estimate and observations. Progress in Oceanography, 198, (2021): 102685, https://doi.org/10.1016/j.pocean.2021.102685.The Atlantic Water (AW) Layer in the Arctic Subpolar gyre sTate Estimate Release 1 (ASTE R1), a data-constrained, regional, medium-resolution coupled ocean-sea ice model, is analyzed for the period 2004–2017 in combination with available hydrographic data. The study, focusing on AW defined as the waters between two bounding isopycnals, examines the time-average, mean seasonal cycle and interannual variability of AW Layer properties and circulation. A surge of AW, marked by rapid increases in mean AW Layer potential temperature and AW Layer thickness, begins two years into the state estimate and traverses the Arctic Ocean along boundary current pathways at a speed of 1–2 cm/s. The surge also alters AW circulation, including a reversal in flow direction along the Lomonosov Ridge, resulting in a new quasi-steady AW circulation from 2010 through the end of the state estimate period. The time-mean AW circulation during this latter time period indicates that a significant amount of AW spreads over the Lomonosov Ridge rather than directly returning along the ridge to Fram Strait. A three-layer depiction of the time-averaged ASTE R1 overturning circulation within the Arctic Ocean reveals that more AW is converted to colder, fresher Surface Layer water than is transformed to Deep and Bottom Water (1.2 Sv vs. 0.4 Sv). ASTE R1 also exhibits an increase in the volume of AW over the study period at a rate of 1.4 Sv, with near compensating decrease in Deep and Bottom Water volume. Observed AW properties compared to ASTE R1 output reveal increasing misfit during the simulated period with the ASTE R1 AW Layer generally being warmer and thicker than in observations.This work is based on the dissertation of the lead author submitted in partial requirement of a M.S. degree from the Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program in Oceanography. The lead author’s participation was funded by the United States Navy’s Civilian Institution (CIVINS) Program. The contributions to this study by the junior authors were supported by the National Science Foundation (JMT and RAK grant PLR-1603660; ATN grant NSF-OPP-1603903)

Mammalian diseases of phosphatidylinositol transfer proteins and their homologs

Inositol and phosphoinositide signaling pathways represent major regulatory systems in eukaryotes. The physiological importance of these pathways is amply demonstrated by the variety of diseases that involve derangements in individual steps in inositide and phosphoinositide production and degradation. These diseases include numerous cancers, lipodystrophies and neurological syndromes. Phosphatidylinositol transfer proteins (PITPs) are emerging as fascinating regulators of phosphoinositide metabolism. Recent advances identify PITPs (and PITP-like proteins) to be coincidence detectors, which spatially and temporally coordinate the activities of diverse aspects of the cellular lipid metabolome with phosphoinositide signaling. These insights are providing new ideas regarding mechanisms of inherited mammalian diseases associated with derangements in the activities of PITPs and PITP-like proteins

Inelastic scattering of a photon by a quantum phase-slip

Spontaneous decay of a single photon is a notoriously inefficient process in nature irrespective of the frequency range. We report that a quantum phase-slip fluctuation in high-impedance superconducting waveguides can split a single incident microwave photon into a large number of lower-energy photons with a near unit probability. The underlying inelastic photon-photon interaction has no analogs in non-linear optics. Instead, the measured decay rates are explained without adjustable parameters in the framework of a new model of a quantum impurity in a Luttinger liquid. Our result connects circuit quantum electrodynamics to critical phenomena in two-dimensional boundary quantum field theories, important in the physics of strongly-correlated systems. The photon lifetime data represents a rare example of verified and useful quantum many-body simulation.Comment: minor revision for clarity, supplementary material is available at www.superconducting-circuits.co

Tomographic and tension analysis of polypropylene reinforced with carbon fiber fabric by injection molding

The use of thermoplastic materials has had significant growth in recent years. However, with great mechanical requirements, thermoplastics have limitations to their use. To improve these restrictions, these materials are reinforced to obtain better properties. Polypropylene is one of the most versatile polymers and is used in almost all modern industries. Thus, the aim of this study is to create composite materials that offer performance for various industrial fields using carbon fiber fabric reinforcement, which is an inexpensive material widely used by the aerospace, automotive, and marine industries. The samples are produced by the over-injection molding of polypropylene. The investigation is focused on the impact of two critical control parameters in the injection molding process: temperature and pressure. Twelve experiments have therefore been considered, taking into account the combination of three factors: the presence or absence of carbon fiber fabric reinforcement, three levels of temperature (200 °C, 220 °C, and 240 °C), and two injection pressures (5000 kPa and 10,000 kPa). To evaluate the influence of these factors, three analyses were carried out: first, on the samples’ shrinkage using a portable metrology-grade 3D laser scanner; second, on the internal defects using computed tomography (CT); and third, on the mechanical properties with tensile tests. From the results obtained, it is observed that the mold shrinkage fell slightly when PP samples were reinforced with carbon fiber, with both materials (PP and carbon-fiber-reinforced PP) having linear behavior with temperature. It is also noticed that polypropylene behaves as a crystalline material when processed at higher temperatures and pressures. From tests on the mechanical properties, it is concluded that the mean yield strength of PP-CF for injection temperatures of 220 °C and 240 °C represents an increase of 43% compared to the non-reinforced material