5,887 research outputs found
Industrial applications of electron accelerators
This paper addresses the industrial applications of electron accelerators for modifying the physical, chemical or biological properties of materials and commercial products by treatment with ionizing radiation. Many beneficial effects can be obtained with these methods, which are known as radiation processing. The earliest practical applications occurred during the 1950s, and the business of radiation processing has been expanding since that time. The most prevalent applications are the modification of many different plastic and rubber products and the sterilization of single-use medical devices. Emerging applications are the pasteurization and preservation of foods and the treatment of toxic industrial wastes. Industrial accelerators can now provide electron energies greater than 10 MeV and average beam powers as high as 700 kW. The availability of high-energy, high-power electron beams is stimulating interest in the use of X-rays (bremsstrahlung) as an alternative to gamma rays from radioactive nuclides
On the shot-noise limit of a thermal current
The noise power spectral density of a thermal current between two macroscopic
dielectric bodies held at different temperatures and connected only at a
quantum point contact is calculated. Assuming the thermal energy is carried
only by phonons, we model the quantum point contact as a mechanical link,
having a harmonic spring potential. In the weak coupling, or weak-link limit,
we find the thermal current analog of the well-known electronic shot-noise
expression.Comment: 4 pages, 1 figur
Superconducting Qubits Coupled to Nanoelectromechanical Resonators: An Architecture for Solid-State Quantum Information Processing
We describe the design for a scalable, solid-state
quantum-information-processing architecture based on the integration of
GHz-frequency nanomechanical resonators with Josephson tunnel junctions, which
has the potential for demonstrating a variety of single- and multi-qubit
operations critical to quantum computation. The computational qubits are
eigenstates of large-area, current-biased Josephson junctions, manipulated and
measured using strobed external circuitry. Two or more of these phase qubits
are capacitively coupled to a high-quality-factor piezoelectric
nanoelectromechanical disk resonator, which forms the backbone of our
architecture, and which enables coherent coupling of the qubits. The integrated
system is analogous to one or more few-level atoms (the Josephson junction
qubits) in an electromagnetic cavity (the nanomechanical resonator). However,
unlike existing approaches using atoms in electromagnetic cavities, here we can
individually tune the level spacing of the ``atoms'' and control their
``electromagnetic'' interaction strength. We show theoretically that quantum
states prepared in a Josephson junction can be passed to the nanomechanical
resonator and stored there, and then can be passed back to the original
junction or transferred to another with high fidelity. The resonator can also
be used to produce maximally entangled Bell states between a pair of Josephson
junctions. Many such junction-resonator complexes can assembled in a
hub-and-spoke layout, resulting in a large-scale quantum circuit. Our proposed
architecture combines desirable features of both solid-state and cavity quantum
electrodynamics approaches, and could make quantum information processing
possible in a scalable, solid-state environment.Comment: 20 pages, 14 separate low-resolution jpeg figure
Hot electrons in low-dimensional phonon systems
A simple bulk model of electron-phonon coupling in metals has been
surprisingly successful in explaining experiments on metal films that actually
involve surface- or other low-dimensional phonons. However, by an exact
application of this standard model to a semi-infinite substrate with a free
surface, making use of the actual vibrational modes of the substrate, we show
that such agreement is fortuitous, and that the model actually predicts a
low-temperature crossover from the familiar T^5 temperature dependence to a
stronger T^6 log T scaling. Comparison with existing experiments suggests a
widespread breakdown of the standard model of electron-phonon thermalization in
metals
Phase rigidity breaking in open Aharonov-Bohm ring coupled to a cantilever
The conductance and the transmittance phase shifts of a two-terminal
Aharonov-Bohm (AB) ring are analyzed in the presence of mechanical
displacements due to coupling to an external can- tilever. We show that phase
rigidity is broken, even in the linear response regime, by means of inelastic
scattering due to phonons. Our device provides a way of observing continuous
variation of the transmission phase through a two-terminal
nano-electro-mechanical system (NEMS). We also propose measurements of phase
shifts as a way to determine the strength of the electron-phonon coupling in
NEMS.Comment: 7 pages, 8 figure
Spintronics of a Nanoelectromechanical Shuttle
We consider effects of the spin degree of freedom on the nanomechanics of a
single-electron transistor (SET) containing a nanometer-sized metallic cluster
suspended between two magnetic leads. It is shown that in such a
nanoelectromechanical SET(NEM-SET) the onset of an electromechanical
instability leading to cluster vibrations and "shuttle" transport of electrons
between the leads can be controlled by an external magnetic field. Different
stable regimes of this spintronic NEM-SET operation are analyzed. Two different
scenarios for the onset of shuttle vibrations are found.Comment: 4 pages, 3 figure
Quantum Shuttle Phenomena in a Nanoelectromechanical Single-Electron Transistor
An analytical analysis of quantum shuttle phenomena in a
nanoelectromechanical single-electron transistor has been performed in the
realistic case, when the electron tunnelling length is much greater than the
amplitude of the zero point oscillations of the central island. It is shown
that when the dissipation is below a certain threshold value, the vibrational
ground state of the central island is unstable. The steady-state into which
this instability develops is studied. It is found that if the electric field
between the leads is much greater than a characteristic value , the quasiclassical shuttle picture is recovered, while if a new quantum regime of shuttle vibrations occurs. We show
that in the latter regime small quantum fluctuations result in large (i.e.
finite in the limit ) shuttle vibrations.Comment: 5 pages, 1 figur
Dynamics of a suspended nanowire driven by an ac Josephson current in an inhomogeneous magnetic field
We consider a voltage-biased nanoelectromechanical Josephson junction, where
a suspended nanowire forms a superconducting weak-link, in an inhomogeneous
magnetic field. We show that a nonlinear coupling between the Josephson current
and the magnetic field generates a Laplace force that induces a whirling motion
of the nanowire. By performing an analytical and a numerical analysis, we
demonstrate that at resonance, the amplitude-phase dynamics of the whirling
movement present different regimes depending on the degree of inhomogeneity of
the magnetic field: time independent, periodic and chaotic. Transitions between
these regimes are also discussed.Comment: 7 pages, 5 figure
Noise-enabled precision measurements of a Duffing nanomechanical resonator
We report quantitative experimental measurements of the nonlinear response of
a radiofrequency mechanical resonator, with very high quality factor, driven by
a large swept-frequency force. We directly measure the noise-free transition
dynamics between the two basins of attraction that appear in the nonlinear
regime, and find good agreement with those predicted by the one-dimensional
Duffing equation of motion. We then measure the response of the transition
rates to controlled levels of white noise, and extract the activation energy
from each basin. The measurements of the noise-induced transitions allow us to
obtain precise values for the critical frequencies, the natural resonance
frequency, and the cubic nonlinear parameter in the Duffing oscillator, with
direct applications to high sensitivity parametric sensors based on these
resonators.Comment: 5 pages, 5 figure
Nonlinear modal interactions in clamped-clamped mechanical resonators
A theoretical and experimental investigation is presented on the intermodal
coupling between the flexural vibration modes of a single clamped-clamped beam.
Nonlinear coupling allows an arbitrary flexural mode to be used as a
self-detector for the amplitude of another mode, presenting a method to measure
the energy stored in a specific resonance mode. Experimentally observed complex
nonlinear dynamics of the coupled modes are quantitatively captured by a model
which couples the modes via the beam extension; the same mechanism is
responsible for the well-known Duffing nonlinearity in clamped-clamped beams.Comment: 5 pages, 3 figure
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