34 research outputs found
Coarse-Grained Picture for Controlling Quantum Chaos
We propose a coarse-grained picture to analyze control problems for quantum
chaos systems. Using optimal control theory, we first show that almost perfect
control is achieved for random matrix systems and a quantum kicked rotor.
Second, under the assumption that the controlled dynamics is well described by
a Rabi-type oscillaion between unperturbed states, we derive an analytic
expression for the optimal field. Finally we numerically confirm that the
analytic field can steer an initial state to a target state in random matrix
systems.Comment: REVTeX4 with graphicx package, 11 pages, 10 figures; replaced
fig.1(a) and 2(a
Trade-off between power extraction maximisation and fatigue reduction in wind farms via second-order sliding mode control and min–max optimisation
Fast coherent control of nitrogen-14 spins associated with nitrogen-vacancy centers in diamonds using dynamical decoupling
A nitrogen-vacancy (NV) center in a diamond enables the access to an electron
spin, which is expected to present highly sensitive quantum sensors. Although
exploiting a nitrogen nuclear spin improves the sensitivity, manipulating it
using a resonant pulse requires a long gate time owing to its small
gyromagnetic ratio. Another technique to control nuclear spins is a conditional
rotation gate based on dynamical decoupling, which is faster but unavailable
for nitrogen spins owing to the lack of transverse hyperfine coupling with the
electron spin. In this study, we generated effective transverse coupling by
applying a weak off-axis magnetic field. An effective coupling depends on the
off-axis field; the conditional rotation gate on the nitrogen-14 spins of an NV
center was demonstrated within 4.2 {\mu}s under an 1.8% off-axis field and a
longitudinal field of approximately 280 mT. We estimated that a population
transfer from the electron to nitrogen spins can be implemented with 8.7
{\mu}s. Our method is applicable to an ensemble of NV centers, in addition to a
single NV center
Dynamical aspects of quantum entanglement for weakly coupled kicked tops
We investigate how the dynamical production of quantum entanglement for
weakly coupled, composite quantum systems is influenced by the chaotic dynamics
of the corresponding classical system, using coupled kicked tops. The linear
entropy for the subsystem (a kicked top) is employed as a measure of
entanglement. A perturbative formula for the entanglement production rate is
derived. The formula contains a correlation function that can be evaluated only
from the information of uncoupled tops. Using this expression and the
assumption that the correlation function decays exponentially which is
plausible for chaotic tops, it is shown that {\it the increment of the strength
of chaos does not enhance the production rate of entanglement} when the
coupling is weak enough and the subsystems (kicked tops) are strongly chaotic.
The result is confirmed by numerical experiments. The perturbative approach is
also applied to a weakly chaotic region, where tori and chaotic sea coexist in
the corresponding classical phase space, to reexamine a recent numerical study
that suggests an intimate relationship between the linear stability of the
corresponding classical trajectory and the entanglement production rate.Comment: 16 pages, 11 figures, submitted to Phys. Rev.
Reactive ion etching of poly(vinylidene fluoride-trifluoroethylene) copolymer for flexible piezoelectric devices
The Japanese Clinical Practice Guideline for acute kidney injury 2016
Acute kidney injury (AKI) is a syndrome which has a broad range of etiologic factors depending on different clinical settings. Because AKI has significant impacts on prognosis in any clinical settings, early detection and intervention are necessary to improve the outcomes of AKI patients. This clinical guideline for AKI was developed by a multidisciplinary approach with nephrology, intensive care medicine, blood purification, and pediatrics. Of note, clinical practice for AKI management which was widely performed in Japan was also evaluated with comprehensive literature search
Simple Synchronous and Asynchronous Algorithms for Distributed Minimax Optimization
Synchronous and asynchronous algorithms are presented for distributed minimax optimization. The objective here is to realize the minimization of the maximum of component functions over the standard multi-agent network, where each node of the network knows its own function and it exchanges its decision variable with its neighbors. In fact, the proposed algorithms are standard consensus and gossip based subgradient methods, while the original minimax optimization is recast as minimization of the sum of component functions by using a p-norm approximation. A scalable step size depending on the approximation ratio p is also presented in order to avoid slow convergence. Numerical examples illustrate that the algorithms with this step size work well even in the high approximation ratios