1,394 research outputs found
Microwave band on-chip coil technique for single electron spin resonance in a quantum dot
Microwave band on-chip microcoils are developed for the application to single
electron spin resonance measurement with a single quantum dot. Basic properties
such as characteristic impedance and electromagnetic field distribution are
examined for various coil designs by means of experiment and simulation. The
combined setup operates relevantly in the experiment at dilution temperature.
The frequency responses of the return loss and Coulomb blockade current are
examined. Capacitive coupling between a coil and a quantum dot causes photon
assisted tunneling, whose signal can greatly overlap the electron spin
resonance signal. To suppress the photon assisted tunneling effect, a technique
for compensating for the microwave electric field is developed. Good
performance of this technique is confirmed from measurement of Coulomb blockade
oscillations.Comment: 7 pages, 8 figures, Accepted for publication in Rev. Sci. Instrum.
The bibliography file is update
Spin-Echo Measurements for an Anomalous Quantum Phase of 2D Helium-3
Previous heat-capacity measurements of our group had shown the possible
existence of an anomalous quantum phase containing the zero-point vacancies
(ZPVs) in 2D He. The system is monolayer He adsorbed on graphite
preplated with monolayer He at densities () just below the 4/7
commensurate phase (). We carried out
pulsed-NMR measurements in order to examine the microscopic and dynamical
nature of this phase. The measured decay of spin echo signals shows the
non-exponential behaviour. The decay curve can be fitted with the double
exponential function, but the relative intensity of the component with a longer
time constant is small (5%) and does not depend on density and temperature,
which contradicts the macroscopic fluid and 4/7 phase coexistence model. This
slowdown is likely due to the mosaic angle spread of Grafoil substrate and the
anisotropic spin-spin relaxation time in 2D systems with respect to the
magnetic field direction. The inverse value deduced from the major echo
signal with a shorter time constant, which obeys the single exponential
function, decreases linearly with decreasing density from , supporting the
ZPV model.Comment: 4 pages, 6 figure
Surface tension in an intrinsic curvature model with fixed one-dimensional boundaries
A triangulated fixed connectivity surface model is investigated by using the
Monte Carlo simulation technique. In order to have the macroscopic surface
tension \tau, the vertices on the one-dimensional boundaries are fixed as the
edges (=circles) of the tubular surface in the simulations. The size of the
tubular surface is chosen such that the projected area becomes the regular
square of area A. An intrinsic curvature energy with a microscopic bending
rigidity b is included in the Hamiltonian. We found that the model undergoes a
first-order transition of surface fluctuations at finite b, where the surface
tension \tau discontinuously changes. The gap of \tau remains constant at the
transition point in a certain range of values A/N^\prime at sufficiently large
N^\prime, which is the total number of vertices excluding the fixed vertices on
the boundaries. The value of \tau remains almost zero in the wrinkled phase at
the transition point while \tau remains negative finite in the smooth phase in
that range of A/N^\prime.Comment: 12 pages, 8 figure
Phase transitions of an intrinsic curvature model on dynamically triangulated spherical surfaces with point boundaries
An intrinsic curvature model is investigated using the canonical Monte Carlo
simulations on dynamically triangulated spherical surfaces of size upto N=4842
with two fixed-vertices separated by the distance 2L. We found a first-order
transition at finite curvature coefficient \alpha, and moreover that the order
of the transition remains unchanged even when L is enlarged such that the
surfaces become sufficiently oblong. This is in sharp contrast to the known
results of the same model on tethered surfaces, where the transition weakens to
a second-order one as L is increased. The phase transition of the model in this
paper separates the smooth phase from the crumpled phase. The surfaces become
string-like between two point-boundaries in the crumpled phase. On the
contrary, we can see a spherical lump on the oblong surfaces in the smooth
phase. The string tension was calculated and was found to have a jump at the
transition point. The value of \sigma is independent of L in the smooth phase,
while it increases with increasing L in the crumpled phase. This behavior of
\sigma is consistent with the observed scaling relation \sigma \sim (2L/N)^\nu,
where \nu\simeq 0 in the smooth phase, and \nu=0.93\pm 0.14 in the crumpled
phase. We should note that a possibility of a continuous transition is not
completely eliminated.Comment: 15 pages with 10 figure
Metabolic profiles of six African cultivars of cassava (Manihot esculenta Crantz) highlight bottlenecks of root yield
Open Access Article; Published online: 17 Jan 2020Cassava is an important staple crop in sub‐Saharan Africa, due to its high productivity even on nutrient poor soils. The metabolic characteristics underlying this high productivity are poorly understood including the mode of photosynthesis, reasons for the high rate of photosynthesis, the extent of source/sink limitation, the impact of environment, and the extent of variation between cultivars. Six commercial African cassava cultivars were grown in a greenhouse in Erlangen, Germany, and in the field in Ibadan, Nigeria. Source leaves, sink leaves, stems and storage roots were harvested during storage root bulking and analyzed for sugars, organic acids, amino acids, phosphorylated intermediates, minerals, starch, protein, activities of enzymes in central metabolism and yield traits. High ratios of RuBisCO:phosphoenolpyruvate carboxylase activity support a C3 mode of photosynthesis. The high rate of photosynthesis is likely to be attributed to high activities of enzymes in the Calvin–Benson cycle and pathways for sucrose and starch synthesis. Nevertheless, source limitation is indicated because root yield traits correlated with metabolic traits in leaves rather than in the stem or storage roots. This situation was especially so in greenhouse‐grown plants, where irradiance will have been low. In the field, plants produced more storage roots. This was associated with higher AGPase activity and lower sucrose in the roots, indicating that feedforward loops enhanced sink capacity in the high light and low nitrogen environment in the field. Overall, these results indicated that carbon assimilation rate, the K battery, root starch synthesis, trehalose, and chlorogenic acid accumulation are potential target traits for genetic improvement
Gallot-Tanno Theorem for closed incomplete pseudo-Riemannian manifolds and applications
We extend the Gallot-Tanno Theorem to closed pseudo-Riemannian manifolds. It
is done by showing that if the cone over a manifold admits a parallel symmetric
tensor then it is Riemannian. Applications of this result to the
existence of metrics with distinct Levi-Civita connections but having the same
unparametrized geodesics and to the projective Obata conjecture are given. We
also apply our result to show that the holonomy group of a closed
-manifold does not preserve any nondegenerate splitting of
.Comment: minor correction
Charge degree of freedom and single-spin fluid model in YBa_2Cu_4O_8
We present a 17O nuclear magnetic resonance study in the stoichiometric
superconductor YBa_2Cu_4O_8. A double irradiation method enables us to show
that, below around 180 K, the spin-lattice relaxation rate of plane oxygen is
not only driven by magnetic, but also significantly by quadrupolar
fluctuations, i.e. low-frequency charge fluctuations. In the superconducting
state, on lowering the temperature, the quadrupolar relaxation diminishes
faster than the magnetic one. These findings show that, with the opening of the
pseudo spin gap, a charge degree of freedom of mainly oxygen character is
present in the electronic low-energy excitation spectrum.Comment: 4 pages, 3 figures, REVTE
Wigner formula of rotation matrices and quantum walks
Quantization of a random-walk model is performed by giving a qudit (a
multi-component wave function) to a walker at site and by introducing a quantum
coin, which is a matrix representation of a unitary transformation. In quantum
walks, the qudit of walker is mixed according to the quantum coin at each time
step, when the walker hops to other sites. As special cases of the quantum
walks driven by high-dimensional quantum coins generally studied by Brun,
Carteret, and Ambainis, we study the models obtained by choosing rotation as
the unitary transformation, whose matrix representations determine quantum
coins. We show that Wigner's -dimensional unitary representations of
rotations with half-integers 's are useful to analyze the probability laws
of quantum walks. For any value of half-integer , convergence of all moments
of walker's pseudovelocity in the long-time limit is proved. It is generally
shown for the present models that, if is even, the probability measure
of limit distribution is given by a superposition of terms of scaled
Konno's density functions, and if is odd, it is a superposition of
terms of scaled Konno's density functions and a Dirac's delta function at the
origin. For the two-, three-, and four-component models, the probability
densities of limit distributions are explicitly calculated and their dependence
on the parameters of quantum coins and on the initial qudit of walker is
completely determined. Comparison with computer simulation results is also
shown.Comment: v2: REVTeX4, 15 pages, 4 figure
Electrically driven single electron spin resonance in a slanting Zeeman field
The rapidly rising fields of spintronics and quantum information science have
led to a strong interest in developing the ability to coherently manipulate
electron spins. Electron spin resonance (ESR) is a powerful technique to
manipulate spins that is commonly achieved by applying an oscillating magnetic
field. However, the technique has proven very challenging when addressing
individual spins. In contrast, by mixing the spin and charge degrees of freedom
in a controlled way through engineered non-uniform magnetic fields, electron
spin can be manipulated electrically without the need of high-frequency
magnetic fields. Here we realize electrically-driven addressable spin rotations
on two individual electrons by integrating a micron-size ferromagnet to a
double quantum dot device. We find that the electrical control and spin
selectivity is enabled by the micro-magnet's stray magnetic field which can be
tailored to multi-dots architecture. Our results demonstrate the feasibility of
manipulating electron spins electrically in a scalable way.Comment: 25 pages, 6 figure
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