6,766 research outputs found
Phonon emission and arrival times of electrons from a single-electron source
In recent charge-pump experiments, single electrons are injected into quantum Hall edge channels at energies significantly above the Fermi level. We consider here the relaxation of these hot edge-channel electrons through longitudinal-optical-phonon emission. Our results show that the probability for an electron in the outermost edge channel to emit one or more phonons en route to a detector some microns distant along the edge channel suffers a double-exponential suppression with increasing magnetic field. This explains recent experimental observations. We also describe how the shape of the arrival-time distribution of electrons at the detector reflects the velocities of the electronic states post phonon emission. We show how this can give rise to pronounced oscillations in the arrival-time-distribution width as a function of magnetic field or electron energy
Picosecond coherent electron motion in a silicon single-electron source
Understanding ultrafast coherent electron dynamics is necessary for
application of a single-electron source to metrological standards, quantum
information processing, including electron quantum optics, and quantum sensing.
While the dynamics of an electron emitted from the source has been extensively
studied, there is as yet no study of the dynamics inside the source. This is
because the speed of the internal dynamics is typically higher than 100 GHz,
beyond state-of-the-art experimental bandwidth. Here, we theoretically and
experimentally demonstrate that the internal dynamics in a silicon
singleelectron source comprising a dynamic quantum dot can be detected,
utilising a resonant level with which the dynamics is read out as
gate-dependent current oscillations. Our experimental observation and
simulation with realistic parameters show that an electron wave packet
spatially oscillates quantum-coherently at 200 GHz inside the source.
Our results will lead to a protocol for detecting such fast dynamics in a
cavity and offer a means of engineering electron wave packets. This could allow
high-accuracy current sources, high-resolution and high-speed
electromagnetic-field sensing, and high-fidelity initialisation of flying
qubits
Galactic-Center Hyper-Shell Model for the North Polar Spurs
The bipolar-hyper shell (BHS) model for the North Polar Spurs (NPS-E, -W, and
Loop I) and counter southern spurs (SPS-E and -W) is revisited based on
numerical hydrodynamical simulations. Propagations of shock waves produced by
energetic explosive events in the Galactic Center are examined. Distributions
of soft X-ray brightness on the sky at 0.25, 0.7, and 1.5 keV in a +/-50 deg x
+/-50 deg region around the Galactic Center are modeled by thermal emission
from high-temperature plasma in the shock-compressed shell considering
shadowing by the interstellar HI and H2 gases. The result is compared with the
ROSAT wide field X-ray images in R2, 4 and 6 bands. The NPS and southern spurs
are well reproduced by the simulation as shadowed dumbbell-shaped shock waves.
We discuss the origin and energetics of the event in relation to the starburst
and/or AGN activities in the Galactic Center. [ High resolution pdf is
available at http://www.ioa.s.u-tokyo.ac.jp/~sofue/htdocs/2016bhs/ ]Comment: 13 pages, 20 figures; To appear in MNRA
Pulse-induced acoustoelectric vibrations in surface-gated GaAs-based quantum devices
We present the results of a numerical investigation which show the excitation
of acoustoelectric modes of vibration in GaAs-based heterostructures due to
sharp nano-second electric-field pulses applied across surface gates. In
particular, we show that the pulses applied in quantum information processing
applications are capable of exciting acoustoelectric modes of vibration
including surface acoustic modes which propagate for distances greater than
conventional device dimensions. We show that the pulse-induced acoustoelectric
vibrations are capable of inducing significant undesired perturbations to the
evolution of quantum systems.Comment: To be published in Phys. Rev.
Needle Tip Force Estimation using an OCT Fiber and a Fused convGRU-CNN Architecture
Needle insertion is common during minimally invasive interventions such as
biopsy or brachytherapy. During soft tissue needle insertion, forces acting at
the needle tip cause tissue deformation and needle deflection. Accurate needle
tip force measurement provides information on needle-tissue interaction and
helps detecting and compensating potential misplacement. For this purpose we
introduce an image-based needle tip force estimation method using an optical
fiber imaging the deformation of an epoxy layer below the needle tip over time.
For calibration and force estimation, we introduce a novel deep learning-based
fused convolutional GRU-CNN model which effectively exploits the
spatio-temporal data structure. The needle is easy to manufacture and our model
achieves a mean absolute error of 1.76 +- 1.5 mN with a cross-correlation
coefficient of 0.9996, clearly outperforming other methods. We test needles
with different materials to demonstrate that the approach can be adapted for
different sensitivities and force ranges. Furthermore, we validate our approach
in an ex-vivo prostate needle insertion scenario.Comment: Accepted for Publication at MICCAI 201
Coulomb Blockade and Kondo Effect in a Quantum Hall Antidot
We propose a general capacitive model for an antidot, which has two localized
edge states with different spins in the quantum Hall regime. The capacitive
coupling of localized excess charges, which are generated around the antidot
due to magnetic flux quantization, and their effective spin fluctuation can
result in Coulomb blockade, h/(2e) Aharonov-Bohm oscillations, and the Kondo
effect. The resultant conductance is in qualitative agreement with recent
experimental data.Comment: 3 figures, to appear in Physical Review Letter
A numerical investigation of a piezoelectric surface acoustic wave interaction with a one-dimensional channel
We investigate the propagation of a piezoelectric surface acoustic wave (SAW)
across a GaAs/AlGaAs heterostructure surface, on which there is
fixed a metallic split-gate. Our method is based on a finite element
formulation of the underlying equations of motion, and is performed in
three-dimensions fully incorporating the geometry and material composition of
the substrate and gates. We demonstrate attenuation of the SAW amplitude as a
result of the presence of both mechanical and electrical gates on the surface.
We show that the incorporation of a simple model for the screening by the
two-dimensional electron gas (2DEG), results in a total electric potential
modulation that suggests a mechanism for the capture and release of electrons
by the SAW. Our simulations suggest the absence of any significant turbulence
in the SAW motion which could hamper the operation of SAW based quantum devices
of a more complex geometry.Comment: 8 pages, 8 figure
Electron interactions in an antidot in the integer quantum Hall regime
A quantum antidot, a submicron depletion region in a two-dimensional electron
system, has been actively studied in the past two decades, providing a powerful
tool for understanding quantum Hall systems. In a perpendicular magnetic field,
electrons form bound states around the antidot. Aharonov-Bohm resonances
through such bound states have been experimentally studied, showing interesting
phenomena such as Coulomb charging, h/2e oscillations, spectator modes,
signatures of electron interactions in the line shape, Kondo effect, etc. None
of them can be explained by a simple noninteracting electron approach.
Theoretical models for the above observations have been developed recently,
such as a capacitive-interaction model for explaining the h/2e oscillations and
the Kondo effect, numerical prediction of a hole maximum-density-droplet
antidot ground state, and spin density-functional theory for investigating the
compressibility of antidot edges. In this review, we summarize such
experimental and theoretical works on electron interactions in antidots.Comment: 73 pages, 28 figures, to be published in Physics Reports. The
resolution of some figures is reduced in this uploa
- …