313 research outputs found
Carbon nanotube collimators: fabrications and applications
Apparatus, methods, systems and devices for fabricating individual CNT collimators. Micron size fiber coated CNT samples are synthesized with chemical vapor deposition method and then the individual CNT collimators are fabricated with focused ion beam technique. Unfocused electron beams are successfully propagated through the CNT collimators. The CNT nano-collimators are used for applications including single ion implantation and in high-energy physics, and allow rapid, reliable testing of the transmission of CNT arrays for transport of molecules
Development of a Compact Neutron Source based on Field Ionization Processes
The authors report on the use of carbon nanofiber nanoemitters to ionize
deuterium atoms for the generation of neutrons in a deuterium-deuterium
reaction in a preloaded target. Acceleration voltages in the range of 50-80 kV
are used. Field emission of electrons is investigated to characterize the
emitters. The experimental setup and sample preparation are described and first
data of neutron production are presented. Ongoing experiments to increase
neutron production yields by optimizing the field emitter geometry and surface
conditions are discussed.Comment: 4 pages, 5 figures; IVNC 201
A C*-Algebra for Quantized Principal U(1)-Connections on Globally Hyperbolic Lorentzian Manifolds
The aim of this work is to complete our program on the quantization of connections on arbitrary principal U(1)-bundles over globally hyperbolic Lorentzian manifolds. In particular, we show that one can assign via a covariant functor to any such bundle an algebra of observables which separates gauge equivalence classes of connections. The C 17 -algebra we construct generalizes the usual CCR-algebras since, contrary to the standard field-theoretic models, it is based on a presymplectic Abelian group instead of a symplectic vector space. We prove a no-go theorem according to which neither this functor, nor any of its quotients, satisfies the strict axioms of general local covariance. As a byproduct, we prove that a morphism violates the locality axiom if and only if a certain induced morphism of cohomology groups is non-injective. We then show that fixing any principal U(1)-bundle, there exists a suitable category of sub-bundles for which a quotient of our functor yields a quantum field theory in the sense of Haag and Kastler. We shall provide a physical interpretation of this feature and we obtain some new insights concerning electric charges in locally covariant quantum field theory
Quantum non-demolition measurements of single donor spins in semiconductors
We propose a technique for measuring the state of a single donor electron
spin using a field-effect transistor induced two-dimensional electron gas and
electrically detected magnetic resonance techniques. The scheme is facilitated
by hyperfine coupling to the donor nucleus. We analyze the potential
sensitivity and outline experimental requirements. Our measurement provides a
single-shot, projective, and quantum non-demolition measurement of an
electron-encoded qubit state.Comment: 8+ pages. 4 figures. Published versio
Einselection and Decoherence from an Information Theory Perspective
We introduce and investigate a simple model of conditional quantum dynamics.
It allows for a discussion of the information-theoretic aspects of quantum
measurements, decoherence, and environment-induced superselection
(einselection).Comment: Proceedings of the Planck constant centenary meeting. Uses
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Phonon Induced Spin Dephasing Time of Nitrogen Vacancy Centers in Diamond from First Principles
Spin qubits with long dephasing times are an essential requirement for the
development of new quantum technologies and have many potential applications
ranging from quantum information processing to quantum memories and quantum
networking. Here we report a theoretical study and the calculation of the spin
dephasing time of defect color centers for the negatively charged nitrogen
vacancy center in diamond. We employ ab initio density functional theory to
compute the electronic structure, and extract the dephasing time using a
cumulant expansion approach. We find that phonon-induced dephasing is a
limiting factor for T2 at low temperatures, in agreement with recent
experiments that use dynamical decoupling techniques. This approach can be
generalized to other spin defects in semiconductors, molecular systems, and
other band gapped materials
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Fundamentals of Focused Ion Beam Nanostructural Processing: Below, At, and Above the Surface
This article considers the fundamentals of what happens in a solid when it is impacted by a medium-energy gallium ion. The study of the ion/sample interaction at
the nanometer scale is applicable to most focused ion beam (FIB)–based work even if
the FIB/sample interaction is only a step in the process, for example, micromachining or microelectronics device processing.Whereas the objective in other articles in this issue is to use the FIB tool to characterize a material or to machine a device or transmission electron microscopy sample, the goal of the FIB in this article is to have the FIB/sample interaction itself become the product.To that end, the FIB/sample interaction is
considered in three categories according to geometry:below, at, and above the surface. First, the FIB ions can penetrate the top atom layer(s) and interact below the surface. Ion implantation and ion damage on flat surfaces have been comprehensively examined; however, FIB applications require the further investigation of high doses in three-dimensional profiles.Second, the ions can interact at the surface, where a morphological instability can lead to ripples and surface self-organization, which can depend on boundary conditions for site-specific and compound FIB processing. Third, the FIB may interact above the surface (and/or produce secondary particles that
interact above the surface).Such ion beam–assisted deposition, FIB–CVD (chemical vapor deposition), offers an elaborate complexity in three dimensions with an FIB using a gas injection system. At the nanometer scale, these three regimes—below, at, and above the surface—can require an interdependent understanding to be judiciously controlled by the FIB.Engineering and Applied Science
Short-Pulse, Compressed Ion Beams at the Neutralized Drift Compression Experiment
We have commenced experiments with intense short pulses of ion beams on the
Neutralized Drift Compression Experiment (NDCX-II) at Lawrence Berkeley
National Laboratory, with 1-mm beam spot size within 2.5 ns full-width at half
maximum. The ion kinetic energy is 1.2 MeV. To enable the short pulse duration
and mm-scale focal spot radius, the beam is neutralized in a 1.5-meter-long
drift compression section following the last accelerator cell. A
short-focal-length solenoid focuses the beam in the presence of the volumetric
plasma that is near the target. In the accelerator, the line-charge density
increases due to the velocity ramp imparted on the beam bunch. The scientific
topics to be explored are warm dense matter, the dynamics of radiation damage
in materials, and intense beam and beam-plasma physics including select topics
of relevance to the development of heavy-ion drivers for inertial fusion
energy. Below the transition to melting, the short beam pulses offer an
opportunity to study the multi-scale dynamics of radiation-induced damage in
materials with pump-probe experiments, and to stabilize novel metastable phases
of materials when short-pulse heating is followed by rapid quenching. First
experiments used a lithium ion source; a new plasma-based helium ion source
shows much greater charge delivered to the target.Comment: 4 pages, 2 figures, 1 table. Submitted to the proceedings for the
Ninth International Conference on Inertial Fusion Sciences and Applications,
IFSA 201
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