27,189 research outputs found
Finite temperature Casimir pistons for electromagnetic field with mixed boundary conditions and its classical limit
In this paper, the finite temperature Casimir force acting on a
two-dimensional Casimir piston due to electromagnetic field is computed. It was
found that if mixed boundary conditions are assumed on the piston and its
opposite wall, then the Casimir force always tends to restore the piston
towards the equilibrium position, regardless of the boundary conditions assumed
on the walls transverse to the piston. In contrary, if pure boundary conditions
are assumed on the piston and the opposite wall, then the Casimir force always
tend to pull the piston towards the closer wall and away from the equilibrium
position. The nature of the force is not affected by temperature. However, in
the high temperature regime, the magnitude of the Casimir force grows linearly
with respect to temperature. This shows that the Casimir effect has a classical
limit as has been observed in other literatures.Comment: 14 pages, 3 figures, accepted by Journal of Physics
Enhanced five-port ring circuit reflectometer for synthetic breast tissue dielectric determination
In this study,a Six-port Reflectometer (SPR) with dielectric probe sensor is used to predict relative dielectric,Δr of normal and tumorous breast tissue in frequency range from 2.34GHz to 3.0GHz. Other than that,a superstrate with an exterior copper layer is overlaid on the surface of a primitive Five-port Ring Circuit (FPRC),which is also a denominated,enhanced superstrate FPRC. It is the main component of the SPR and is presented in this paper as well. The enhanced superstrate FPRC is capable of improving its operating bandwidth by 26% and shifting the operating centre frequency to a lower value without increasing circuit physical size. The detailed design and characteristics of the FPRC are described here. In addition,the enhanced superstrate FPRC is integrated into the SPR for one-port reflection coefficient measurement. The measurement using the SPR is benchmarked with Agilentâs E5071C Vector Network Analyzer (VNA) for one-port reflection coefficient. Maximum absolute mean error of the linear magnitude and phase measurements are recorded to be 0.03 and 5.50°,respectively. In addition,maximum absolute error of the predicted dielectric and loss factor are 1.77 and 0.61,respectively
Cross-talk compensation of hyperfine control in donor qubit architectures
We theoretically investigate cross-talk in hyperfine gate control of
donor-qubit quantum computer architectures, in particular the Kane proposal. By
numerically solving the Poisson and Schr\"{o}dinger equations for the gated
donor system, we calculate the change in hyperfine coupling and thus the error
in spin-rotation for the donor nuclear-electron spin system, as the gate-donor
distance is varied. We thus determine the effect of cross-talk - the
inadvertent effect on non-target neighbouring qubits - which occurs due to
closeness of the control gates (20-30nm). The use of compensation protocols is
investigated, whereby the extent of crosstalk is limited by the application of
compensation bias to a series of gates. In light of these factors the
architectural implications are then considered.Comment: 15 pages, 22 figures, submitted to Nanotechnolog
Entanglement and statistics in Hong-Ou-Mandel interferometry
Hong-Ou-Mandel interferometry allows one to detect the presence of
entanglement in two-photon input states. The same result holds for
two-particles input states which obey to Fermionic statistics. In the latter
case however anti-bouncing introduces qualitative differences in the
interferometer response. This effect is analyzed in a Gedankenexperiment where
the particles entering the interferometer are assumed to belong to a
one-parameter family of quons which continuously interpolate between the
Bosonic and Fermionic statistics.Comment: 7 pages, 3 figures; minor editorial changes and new references adde
A possible minimal gauge-Higgs unification
A possible minimal model of the gauge-Higgs unification based on the higher
dimensional spacetime M^4 X (S^1/Z_2) and the bulk gauge symmetry SU(3)_C X
SU(3)_W X U(1)_X is constructed in some details. We argue that the Weinberg
angle and the electromagnetic current can be correctly identified if one
introduces the extra U(1)_X above and a bulk scalar triplet. The VEV of this
scalar as well as the orbifold boundary conditions will break the bulk gauge
symmetry down to that of the standard model. A new neutral zero-mode gauge
boson Z' exists that gains mass via this VEV. We propose a simple fermion
content that is free from all the anomalies when the extra brane-localized
chiral fermions are taken into account as well. The issues on recovering a
standard model chiral-fermion spectrum with the masses and flavor mixing are
also discussed, where we need to introduce the two other brane scalars which
also contribute to the Z' mass in the similar way as the scalar triplet. The
neutrinos can get small masses via a type I seesaw mechanism. In this model,
the mass of the Z' boson and the compactification scale are very constrained as
respectively given in the ranges: 2.7 TeV < m_Z' < 13.6 TeV and 40 TeV < 1/R <
200 TeV.Comment: 20 pages, revised versio
Resonant Coherent Phonon Spectroscopy of Single-Walled Carbon Nanotubes
Using femtosecond pump-probe spectroscopy with pulse shaping techniques, one
can generate and detect coherent phonons in chirality-specific semiconducting
single-walled carbon nanotubes. The signals are resonantly enhanced when the
pump photon energy coincides with an interband exciton resonance, and analysis
of such data provides a wealth of information on the chirality-dependence of
light absorption, phonon generation, and phonon-induced band structure
modulations. To explain our experimental results, we have developed a
microscopic theory for the generation and detection of coherent phonons in
single-walled carbon nanotubes using a tight-binding model for the electronic
states and a valence force field model for the phonons. We find that the
coherent phonon amplitudes satisfy a driven oscillator equation with the
driving term depending on photoexcited carrier density. We compared our
theoretical results with experimental results on mod 2 nanotubes and found that
our model provides satisfactory overall trends in the relative strengths of the
coherent phonon signal both within and between different mod 2 families. We
also find that the coherent phonon intensities are considerably weaker in mod 1
nanotubes in comparison with mod~2 nanotubes, which is also in excellent
agreement with experiment.Comment: 21 pages, 22 figure
Polarization dependence of coherent phonon generation and detection in highly-aligned single-walled carbon nanotubes
We have investigated the polarization dependence of the generation and
detection of radial breathing mode (RBM) coherent phonons (CP) in
highly-aligned single-walled carbon nanotubes. Using polarization-dependent
pump-probe differential-transmission spectroscopy, we measured RBM CPs as a
function of angle for two different geometries. In Type I geometry, the pump
and probe polarizations were fixed, and the sample orientation was rotated,
whereas, in Type II geometry, the probe polarization and sample orientation
were fixed, and the pump polarization was rotated. In both geometries, we
observed a very nearly complete quenching of the RBM CPs when the pump
polarization was perpendicular to the nanotubes. For both Type I and II
geometries, we have developed a microscopic theoretical model to simulate CP
generation and detection as a function of polarization angle and found that the
CP signal decreases as the angle goes from 0 degrees (parallel to the tube) to
90 degrees (perpendicular to the tube). We compare theory with experiment in
detail for RBM CPs created by pumping at the E44 optical transition in an
ensemble of single-walled carbon nanotubes with a diameter distribution
centered around 3 nm, taking into account realistic band structure and
imperfect nanotube alignment in the sample
Metal oxide-graphene field-effect transistor: interface trap density extraction model
A simple to implement model is presented to extract interface trap density of graphene field effect transistors. The presence of interface trap states detrimentally affects the device drain current-gate voltage relationship Ids-Vgs. At the moment, there is no analytical method available to extract the interface trap distribution of metal-oxide-graphene field effect transistor (MOGFET) devices. The model presented here extracts the interface trap distribution of MOGFET devices making use of available experimental capacitance-gate voltage Ctot-Vgs data and a basic set of equations used to define the device physics of MOGFET devices. The model was used to extract the interface trap distribution of 2 experimental devices. Device parameters calculated using the extracted interface trap distribution from the model, including surface potential, interface trap charge and interface trap capacitance compared very well with their respective experimental counterparts. The model enables accurate calculation of the surface potential affected by trap charge. Other models ignore the effect of trap charge and only calculate the ideal surface potential. Such ideal surface potential when used in a surface potential based drain current model will result in an inaccurate prediction of the drain current. Accurate calculation of surface potential that can later be used in drain current model is highlighted as a major advantage of the model
Preparing multi-partite entanglement of photons and matter qubits
We show how to make event-ready multi-partite entanglement between qubits
which may be encoded on photons or matter systems. Entangled states of matter
systems, which can also act as single photon sources, can be generated using
the entangling operation presented in quant-ph/0408040. We show how to entangle
such sources with photon qubits, which may be encoded in the dual rail,
polarization or time-bin degrees of freedom. We subsequently demonstrate how
projective measurements of the matter qubits can be used to create entangled
states of the photons alone. The state of the matter qubits is inherited by the
generated photons. Since the entangling operation can be used to generate
cluster states of matter qubits for quantum computing, our procedure enables us
to create any (entangled) photonic quantum state that can be written as the
outcome of a quantum computer.Comment: 10 pages, 4 figures; to appear in Journal of Optics
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