Quantum Computing

Quantum mechanics---the theory describing the fundamental workings of nature---is famously counterintuitive: it predicts that a particle can be in two places at the same time, and that two remote particles can be inextricably and instantaneously linked. These predictions have been the topic of intense metaphysical debate ever since the theory's inception early last century. However, supreme predictive power combined with direct experimental observation of some of these unusual phenomena leave little doubt as to its fundamental correctness. In fact, without quantum mechanics we could not explain the workings of a laser, nor indeed how a fridge magnet operates. Over the last several decades quantum information science has emerged to seek answers to the question: can we gain some advantage by storing, transmitting and processing information encoded in systems that exhibit these unique quantum properties? Today it is understood that the answer is yes. Many research groups around the world are working towards one of the most ambitious goals humankind has ever embarked upon: a quantum computer that promises to exponentially improve computational power for particular tasks. A number of physical systems, spanning much of modern physics, are being developed for this task---ranging from single particles of light to superconducting circuits---and it is not yet clear which, if any, will ultimately prove successful. Here we describe the latest developments for each of the leading approaches and explain what the major challenges are for the future.Comment: 26 pages, 7 figures, 291 references. Early draft of Nature 464, 45-53 (4 March 2010). Published version is more up-to-date and has several corrections, but is half the length with far fewer reference

Advanced Quantum Electronic and Spin Systems: Artificial Graphene and Nitrogen-Vacancy Centers in Diamond

When nature is observed at the nanoscale, quantum physics is typically the most accurate model to describe and predict its behavior. Furthermore, quantum effects are increasingly at the core of the operation of new advanced electronic and photonic devices, which, in some cases, are designed on the basis of controlling quantum systems. This thesis focuses on two such systems, united by the methods used to realize them. These methods represent the cutting-edge of nanofabrication, which is the structuring of matter at ultra-small dimensions with a degree of precision and control that has not been previously attained. Pushing these methods to their limits enables the emergence of unique phenomena in the quantum systems explored here. The first system involves the realization of artificial graphene in an AlGaAs/GaAs quantum heterostructure. The appearance of massless charge carriers in graphene, which are described by the relativistic Dirac equation, originates from the linear energy-momentum dispersion of the electronic states in proximity to the K and K’ points of the hexagonal Brillouin zone. This unique quantum behavior is a direct result of the honeycomb symmetry of the graphene lattice. The prospect of reproducing this physics in an adjustable, artificial honeycomb lattice, known as artificial graphene, offers a platform for the exploration of novel quantum regimes of massless Dirac fermions beyond the limits imposed by the inability to manipulate the lattice of the natural material. The electronic properties of a two-dimensional electron gas whose density is modulated by a periodic potential with honeycomb symmetry have been predicted to generate massless Dirac-fermions with tunable Fermi velocity. This thesis reports the observation of a graphene-like band structure in a modulation-doped AlGaAs/GaAs quantum well engineered with a honeycomb lateral surface superlattice. This was accomplished by reactive ion etching of the surface to within a few tens of nanometers from the quantum well. A metal hard-mask, patterned by electron beam lithography combined with metal deposition and lift-off, was used to form a honeycomb artificial lattice with a variable lattice period, down to 40 nm. This is a three-fold reduction with respect to the smallest reported to date in pertinent literature. The BCl3-based shallow etching produces cylindrical pillars below which the two-dimensional electron gas is expected to form quantum dots, where the electron density is higher than in the surrounding etched regions. Low-temperature resonant inelastic light scattering measurements reveal new electronic transitions. An accurate interpretation of these can be found in the joint density of states derived from the calculated graphene-like linearly-dispersed energy bands, induced by the honeycomb potential modulation. The second system comprises the nanoscale engineering of individual electron spin qubits in diamond. Spin systems in solid-state have been intensively investigated as an outstanding pathway towards quantum information processing. One of the advantages of solid-state spintronics is the possibility of applying nanofabrication techniques commonly used by the semiconductor industry to produce and integrate spin qubits. The negatively charged nitrogen-vacancy (NV-) center in diamond stands out because of its optically addressable spin, which shows long coherence time and viable spin initiation, manipulation and read-out. A central challenge has been the positioning of NV- centers with nanometer scale control, that would allow for efficient and consistent dipolar coupling and the integration within an optoelectronic device. I demonstrate a method for chip-scale fabrication of arrays of closely-spaced NV- centers with record spatial localization of approximately 10 nm in all three dimensions and controllable inter-NV spacing as small as 40 nm. This is the highest spatial resolution realized to date in positioning NV- centers at the nanoscale with high throughput, and approaches the length scale of strong dipolar coupling. This method used masked implantation of nitrogen in an ultra-pure CVD-grown diamond substrate through nano-apertures in a thin gold film, patterned via electron-beam lithography and dry etching. The high-density and high-atomic weight of gold results in a mask which is significantly thinner than polymer films used in other works, whilst still successfully impeding ion penetration, with a mask contrast of more than 40 dB. This process allows for the creation of apertures with lower aspect ratio which are therefore easier to pattern in close proximity to one another, i.e., within the dipolar coupling range. The position and spin coherence properties of the resulting near-surface NVs were measured through wide-field super-resolution optically detected magnetic resonance imaging, Hahn echo and CPMG pulsed microwave spectroscopy. The patterning methodology demonstrated here is optimally suited to functional integration with plasmonic nanostructures, which can enhance our ability to control single-photon emission with the prospect of creating near-surface nanoscale sensors of electric or magnetic fields and quantum optoelectronic devices

A pairwise substitutional fault tolerance technique for the cube-connected cycles architecture

[[abstract]]With all of the salient features of hypercubes, the cube-connected cycles (CCC) structure is an attractive parallel computation network suited for very large scale integration (VLSI) implementation because of its layout regularity. Unfortunately, the classical CCC structure tends to suffer from considerable performance degradation in the presence of faults. The authors deal with a fault-tolerant CCC structure obtained by incorporating a spare PE in each cycle and by adding extra links among PE's to realize dimensional substitutes for failed PE's in the immediate lower dimension. A unique feature of this design lies in that a faulty PE and its laterally connected PE are always replaced at the same time by their immediate vertical successor pair, achieving pairwise substitution to elegantly maintain the rigid full CCC structure after faulty PE's arise. The proposed structure improves reliability substantially without incurring large overhead in layout area. This design is compared with earlier fault-tolerant CCC designs in terms of normalized reliability, which takes area overhead into account. An extension to this fault-tolerant structure is also discussed[[booktype]]電子

Using MapReduce Streaming for Distributed Life Simulation on the Cloud

Distributed software simulations are indispensable in the study of large-scale life models but often require the use of technically complex lower-level distributed computing frameworks, such as MPI. We propose to overcome the complexity challenge by applying the emerging MapReduce (MR) model to distributed life simulations and by running such simulations on the cloud. Technically, we design optimized MR streaming algorithms for discrete and continuous versions of Conway’s life according to a general MR streaming pattern. We chose life because it is simple enough as a testbed for MR’s applicability to a-life simulations and general enough to make our results applicable to various lattice-based a-life models. We implement and empirically evaluate our algorithms’ performance on Amazon’s Elastic MR cloud. Our experiments demonstrate that a single MR optimization technique called strip partitioning can reduce the execution time of continuous life simulations by 64%. To the best of our knowledge, we are the first to propose and evaluate MR streaming algorithms for lattice-based simulations. Our algorithms can serve as prototypes in the development of novel MR simulation algorithms for large-scale lattice-based a-life models.https://digitalcommons.chapman.edu/scs_books/1014/thumbnail.jp

Bibliography of Lewis Research Center technical publications announced in 1993

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1993. All the publications were announced in the 1993 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Nuclear Fusion Programme: Annual Report of the Association Karlsruhe Institute of Technology/EURATOM ; January 2011 - December 2011 (KIT Scientific Reports ; 7621)

The Karlsruhe Institute of Technology (KIT) is working in the framework of the European Fusion Programme on key technologies in the areas of superconducting magnets, microwave heating systems (Electron-Cyclotron-Resonance-Heating, ECRH), the deuterium-tritium fuel cycle, He-cooled breeding blankets, a He-cooled divertor and structural materials, as well as refractory metals for high heat flux applications including a major participation in the preparation of the international IFMIF project

Additive Manufacturing Research and Applications

This Special Issue book covers a wide scope in the research field of 3D-printing, including: the use of 3D printing in system design; AM with binding jetting; powder manufacturing technologies in 3D printing; fatigue performance of additively manufactured metals, such as the Ti-6Al-4V alloy; 3D-printing methods with metallic powder and a laser-based 3D printer; 3D-printed custom-made implants; laser-directed energy deposition (LDED) process of TiC-TMC coatings; Wire Arc Additive Manufacturing; cranial implant fabrication without supports in electron beam melting (EBM) additive manufacturing; the influence of material properties and characteristics in laser powder bed fusion; Design For Additive Manufacturing (DFAM); porosity evaluation of additively manufactured parts; fabrication of coatings by laser additive manufacturing; laser powder bed fusion additive manufacturing; plasma metal deposition (PMD); as-metal-arc (GMA) additive manufacturing process; and spreading process maps for powder-bed additive manufacturing derived from physics model-based machine learning

Tenth European Powder Diffraction Conference – Geneva, September 1-4, 2006

Zeitschrift für Kristallographie. Supplement Volume 26 presents the complete Proceedings of all contributions to the X European Powder Diffraction Conference in Geneva 2006: Method Development and Application, Instrumental Software Development, Materials Supplement Series of Zeitschrift für Kristallographie publishes Proceedings and Abstracts of international conferences on the interdisciplinary field of crystallography

Particle Physics Reference Library

This second open access volume of the handbook series deals with detectors, large experimental facilities and data handling, both for accelerator and non-accelerator based experiments. It also covers applications in medicine and life sciences. A joint CERN-Springer initiative, the “Particle Physics Reference Library” provides revised and updated contributions based on previously published material in the well-known Landolt-Boernstein series on particle physics, accelerators and detectors (volumes 21A,B1,B2,C), which took stock of the field approximately one decade ago. Central to this new initiative is publication under full open access