Random access actuation of nanowire grid metamaterial

While metamaterials offer engineered static optical properties, future artificial media with dynamic random-access control over shape and position of meta-molecules will provide arbitrary control of light propagation. The simplest example of such a reconfigurable metamaterial is a nanowire grid metasurface with subwavelength wire spacing. Recently we demonstrated computationally that such a metadevice with individually controlled wire positions could be used as dynamic diffraction grating, beam steering module and tunable focusing element. Here we report on the nanomembrane realization of such a nanowire grid metasurface constructed from individually addressable plasmonic chevron nanowires with a 230 nm × 100 nm cross-section, which consist of gold and silicon nitride. The active structure of the metadevice consists of 15 nanowires each 18 μm long and is fabricated by a combination of electron beam lithography and ion beam milling. It is packaged as a microchip device where the nanowires can be individually actuated by control currents via differential thermal expansion

Tunable compact THz devices based on graphene and other 2D material metasurfaces

Since the isolation of graphene in 2004, a large amount of research has been directed at 2D materials and their applications due to their unique characteristics. Compared with the noble metal plasmons in the visible and near-infrared frequencies, graphene can support surface plasmons in the lower frequencies of terahertz (THz) and midinfrared. Especially, the surface conductivity of graphene can be tuned by either chemical doping or electrostatic gating. As a result, the idea of designing graphene metasurfaces is attractive because of its ultra-broadband response and tunability. It has been demonstrated theoretically and experimentally that the third-order nonlinearity of graphene at the THz frequency range is exceptionally strong, and graphene has smaller losses with respect to noble metals. These features make graphene a promising candidate to enhance nonlinear effects at the far-infrared and THz frequencies. In this thesis, we present several designs to explore electromagnetic applications of graphene metasurface. Theoretical and simulation studies are carried out to design tunable THz polarizers, amplifiers, coherent perfect absorbers and to achieve enhanced nonlinear effect. These studies on the applications of monolayer graphene demonstrate prospective potentials of graphene in THz sensing, imaging, modulators, and nonlinear THz spectroscopy. Adviser: Christos Argyropoulo

Novel techniques for quasi three-dimensional nanofabrication of Transformation Optics devices

Current nanofabrication is almost exclusively limited to top-down, two-dimensional techniques. As technology moves more deeply into the nano-scale regime, fabrication of new devices with quasi three-dimensional geometries shows great potential. One excellent example of an emerging field that requires this type of non-conformal 3D fabrication technique is the field of Transformation Optics. This field involves transforming and manipulating the optical space through which light propagates. Arbitrarily manipulating the optical space requires advanced fabrication techniques, which are not possible with current two-dimensional fabrication technologies. One step toward quasi three-dimensional nanofabrication involves employing angled deposition allowing new growth mechanisms, and enabling a new realm of quasi three-dimensional fabrication.^ Transformation optics also has potential for having a huge impact on one of the most fundamental and impactful aspects of optics - the capability of fully controlling and manipulating the phase of light. For this purpose, dielectric metamaterial arrays can be fabricated, altering the phase of light transmitted through the structures, while maintaining a high transmittance (low reflection). By fabricating these structures with a high-index material (such as silicon), a large gradient in phase can be implemented by adjusting the material\u27s effective filling fraction. Using these dielectric metamaterial arrays, anomalous refraction and focusing is demonstrated in films with thicknesses less than one wavelength

Quantum information processing with tunable and low-loss superconducting circuits

The perhaps most promising platform for quantum information processing is the circuit-QED architecture based on superconducting circuits representing quantum bits. These circuits must be made with low losses so that the quantum information is retained for as long as possible. We developed fabrication processes achieving state-of-the-art coherence times of over 100 \ub5s. We identified the primary source of loss to be parasitic two-level systems by studying fluctuations of qubit relaxation times.Using our high-coherence circuits, we implemented a quantum processor built on fixed-frequency qubits and frequency-tunable couplers. The tunable couplers were lumped-element LC resonators, where the inductance came from a superconducting quantum interference device (SQUID). We achieved a controlled-phase gate with a fidelity of 99% by parametric modulation of the coupler frequency. Using this device, and another similar to it, we demonstrated two different quantum algorithms, the quantum approximate optimization algorithm, and density matrix exponentiation. We achieved high algorithmic fidelities, aided by our carefully calibrated gates.Additionally, we researched parametric oscillations using frequency-tunable resonators. Previously, degenerate parametric oscillations have been demonstrated by modulation of the resonant frequency at twice that frequency. We use this phenomenon to implement a readout method for a superconducting qubit with a fidelity of 98.7%. We demonstrated correlated radiation in nondegenerate parametric oscillations by modulating at the sum of two resonant frequencies of a multimode resonator. We showed an excellent quantitative agreement between the classical properties of the oscillations with a theoretical model. Moreover, we studied higher-order modulation at up to five times their resonant frequencies. These types of parametric oscillation states might be used as a quantum resource for continuous-variable quantum computing

Superconducting Circuit Architectures Based on Waveguide Quantum Electrodynamics

Quantum science and technology provides new possibilities in processing information, simulating novel materials, and answering fundamental questions beyond the reach of classical methods. Realizing these goals relies on the advancement of physical platforms, among which superconducting circuits have been one of the leading candidates offering complete control and read-out over individual qubits and the potential to scale up. However, most circuit-based multi-qubit architectures only include nearest-neighbor (NN) coupling between qubits, which limits the efficient implementation of low-overhead quantum error correction and access to a wide range of physical models using analog quantum simulation. This challenge can be overcome by introducing non-local degrees of freedom. For example, photons in a shared channel between qubits can mediate long-range qubit-qubit coupling arising from light-matter interaction. In addition, constructing a scalable architecture requires this channel to be intrinsically extensible, in which case a one-dimensional waveguide is an ideal structure providing the extensible direction as well as strong light-matter interaction. In this thesis, we explore superconducting circuit architectures based on light-matter interactions in waveguide quantum electrodynamics (QED) systems. These architectures in return allow us to study light-matter interaction, demonstrating strong coupling in the open environment of a waveguide by employing sub-radiant states resulting from collective effects. We further engineer the waveguide dispersion to enter the topological photonics regime, exploring interactions between qubits that are mediated by photons with topological properties. Finally, towards the goals of quantum information processing and simulation, we settle into a multi-qubit architecture where the photon-mediated interaction between qubits exhibits tunable range and strength. We use this multi-qubit architecture to construct a lattice with tunable connectivity for strongly interacting microwave photons, synthesizing a quantum many-body model to explore chaotic dynamics. The architectures in this thesis introduce scalable beyond-NN coupling between superconducting qubits, opening the door to the exploration of many-body physics with long-range coupling and efficient implementation of quantum information processing protocols.</p

Molecular Beam Epitaxy of InAs, GaSb, AlSb Structures for Interband Cascade Devices

The interband cascade (IC) family of devices has been extended beyond mid-infrared lasers to include photovoltaic (PV) and photodetector (PD) devices. These devices utilize the transition between conduction and valence bands for photon emission or absorption in the infrared region. The cascade structure recycles electrons to generate or collect multiple photons per electron. Epitaxial growths of the device structures are challenging because they consist of hundreds of quantum wells and require atomic layer precision in thickness control. Molecular beam epitaxy (MBE) was used to grow these structures with InAs, GaSb, AlSb, and their alloys on InAs or GaSb substrates. IC laser structures with InAs plasmon cladding layers were grown on InAs substrates for wavelengths greater than 3 μm. To provide a smooth initial surface for the cascade region, the optimal conditions for growth of homoepitaxial InAs layers were investigated over a wide range of substrate temperatures and As2/In flux ratios at a growth rate of 0.66 monolayer/s (ML/s). Material quality was investigated using differential interference contrast microscopy, scanning electron microscopy, and atomic force microscopy. The geometry of oval hillock defects on the InAs layers suggested that these defects originated at the substrate surface. The InAs-based IC lasers had emission wavelengths out to 11 μm, which is the longest wavelength among interband lasers based on III–V materials. By introducing intermediate superlattice (SL) cladding layers to enhance optical confinement and reduce internal absorption loss, the first continuous wave operation of InAs-based IC lasers at room temperature was demonstrated. The threshold current density of 247 A/cm2 for emission near 4.6 μm is the lowest ever reported among semiconductor mid-infrared lasers at similar wavelengths. ICPV and ICPD devices were developed based on the architecture of IC lasers. They both consist of multiple discrete InAs/GaSb SL absorbers sandwiched between electron and hole barriers. ICPV devices can be used in thermophotovoltaic systems that convert radiant energy from a heat source into electricity. Strain-balanced InAs/GaSb SL structures were achieved by adjusting the group-V overpressure during MBE growth. Two- and three-stage ICPV devices operated at room temperature with substantial open-circuit voltages at a cutoff wavelength of 5.3 μm, the longest ever reported for room-temperature PV devices. The interfaces of InAs/GaSb SLs were studied with the goal of improving the PDs designed for the long-wavelength infrared region. Two ICPD structures with different SL interfaces were grown by MBE, one with a ~1.2 ML-thick InSb layer inserted intentionally only at the GaSb-on-InAs interfaces and another with a ~0.6 ML-thick InSb layer inserted at both InAs-on-GaSb and GaSb-on-InAs interfaces. The material quality of the PD structures was similar according to differential interference contrast microscopy, atomic force microscopy, and x-ray diffraction measurements. The device performances were not substantially different with a detectivity of 3.7×10^10 Jones for 78 K at 8 μm and both operated up to 250K. This good performance implies that the interface quality was reasonably controlled for both interface arrangements. The arrangement of dividing a thick continuous InSb layer at the GaSb-on-InAs interface into thinner InSb layers at both interfaces can be used to achieve strain balance in SL detectors for even longer wavelengths

High-Throughput, Continuous Nanopatterning Technologies for Display and Energy Applications.

The motivation of this work is to enable continuous patterning of nanostructures on flexible substrates to push nanoscale lithography to an entirely new level with drastically increased throughput. The Roll-to-Roll Nanoimprint Lithography (R2RNIL) technology presented in this work retains the high-resolution feature capabilities of traditional NIL, but with an increase in throughput by at least one or two orders of magnitude. We demonstrated large-area (4” wide) continuous imprinting of nanogratings by using a newly developed apparatus capable of roll-to-roll imprinting on flexible substrates (R2RNIL) and roll-to-plate imprinting on rigid substrates (R2PNIL). In addition, analytical models were developed to predict the residual layer thickness in dynamic R2RNIL. As a potential application, high-performance metal wire-grid polarizers have also been fabricated utilizing R2RNIL. Another research focus involved Direct Metal Imprinting (DMI) to create discrete nano-scale metal gratings. DMI uses a polymer cushion layer between a thin metal layer and a hard substrate, which enables room-temperature nanoimprinting of the metal by overcoming troublesome hard-to-hard surface contact issues while preserving the Si mold. We also introduced a novel nanofabrication technique, Dynamic Nano-Inscribing (DNI) for creating truly continuous nanograting patterns by using the sharp edge of a tilted Si mold on a variety of metals or polymer materials, creating linewidths down to 50 nm at extremely high speeds (~100 mm/sec) under ambient conditions. Additionally, a new nanograting fabrication method, Localized Dynamic Wrinkling (LDW) has been developed. LDW enables the continuous formation of micro/nano-scale gratings by simply sliding a flat edge of a cleaved Si wafer over the metal film. LDW shares the same basic principle as the buckling (wrinkling) phenomenon but the moving edge of the tilted Si wafer exerts stress on a metal coated polymer and sequentially generates localized winkles in the metal film in a dynamic fashion. The period in LDW can be controlled by several processing parameters and shows good agreement with a theoretical model. Finally, we developed a Dynamic Nano-Cutting (DNC) process using high-frequency indentations on a moving substrate to sequentially create nanograting patterns. DNC provides perfectly straight lines with real-time period modulation, which is difficult to achieve by other nanomanufacturing techniques.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/76015/1/happyash_1.pd

Superconducting quantum circuits for hybrid architectures

Im Bestreben nach neuen Quantentechnologien gehören supraleitende Quantenschaltkreise (SQS) zu den weltweit führenden Hardware-Plattformen, und finden bereits Anwendung in den Bereichen der Quanteninformationsverarbeitung, Quantenkommunikation und –kryptographie, sowie in der Quantensensorik. Obwohl die Kohärenz solcher Schaltkreise in den vergangenen zwei Jahrzehnten enorm gesteigert werden konnte, existieren konkurrierende Plattformen, die teilweise in bedeutenden Aspekten noch immer überlegen sind. Gerade deshalb erscheint eine Verknüpfung unterschiedlicher Implementierungen zu einer Quantenhybridarchitektur reizvoll, mit dem Ziel, die Stärken der individuellen Plattformen zu kombinieren und gleichzeitig vorhandene Schwächen auszugleichen. In diesem Zusammenhang habe ich im Rahmen meiner Dissertation eine nichtlineare Induktivität für die Verwendung in SQSs entwickelt, die, basierend auf dem ungeordneten Supraleiter „granulares Aluminium“ (grAl), auch in hohen Magnetfeldern verwendet werden kann, was eine Grundvoraussetzung für die Anwendbarkeit in Hybridstrukturen darstellt. Als Machbarkeitsnachweise habe ich den konventionellen Josephson-Kontakt in einem Transmon-Qubit mit dieser grAl-Induktivität ausgetauscht, und die Mikrowelleneigenschaften des Systems im Magnetfeld charakterisiert. Um das Signal-Rausch-Verhältnis der Messung zu verbessern, habe ich zudem einen nicht-entarteten parametrischen Verstärker entwickelt, der auf langen Ketten von Josephson-Kontakten basiert. Die Neuheit des zugrundeliegenden Konzeptes ist dabei die Verwendung von mehreren Eigenmodpaaren der Josephson-Kette, um den Frequenzbereich zwischen 1 und 10 GHz möglichst mit einem einzigen Verstärker abzudecken

Strategic Latency Unleashed: The Role of Technology in a Revisionist Global Order and the Implications for Special Operations Forces

The article of record may be found at https://cgsr.llnl.govThis work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344. The views and opinions of the author expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC. ISBN-978-1-952565-07-6 LCCN-2021901137 LLNL-BOOK-818513 TID-59693This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE-AC52-07NA27344. The views and opinions of the author expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC. ISBN-978-1-952565-07-6 LCCN-2021901137 LLNL-BOOK-818513 TID-5969