12 research outputs found
Triangular and Honeycomb Lattices of Cold Atoms in Optical Cavities
We consider a two-dimensional homogeneous ensemble of cold bosonic atoms
loaded inside two optical cavities and pumped by a far-detuned external laser
field. We examine the conditions for these atoms to self-organize into
triangular and honeycomb lattices as a result of superradiance. By collectively
scattering the pump photons, the atoms feed the initially empty cavity modes.
As a result, the superposition of the pump and cavity fields creates a
space-periodic light-shift external potential and atoms self-organize into the
potential wells of this optical lattice. Depending on the phase of the cavity
fields with respect to the pump laser, these minima can either form a
triangular or a hexagonal lattice. By numerically solving the dynamical
equations of the coupled atom-cavity system, we have shown that the two stable
atomic structures at long times are the triangular lattice and the honeycomb
lattice with equally-populated sites. We have also studied how to drive atoms
from one lattice structure to another by dynamically changing the phase of the
cavity fields with respect to the pump laser
Optimized Cooper pair pumps
In adiabatic Cooper pair pumps, operated by means of gate voltage modulation
only, the quantization of the pumped charge during a cycle is limited due to
the quantum coherence of the macroscopic superconducting wave function. In this
work we show that it is possible to obtain very accurate pumps in the
non-adiabatic regime by a suitable choice of the shape of the gate voltage
pulses. We determine the shape of these pulses by applying quantum optimal
control theory to this problem. In the optimal case the error, with respect to
the quantized value, can be as small as of the order of (10E-6)e: the error is
reduced by up to five orders of magnitude with respect to the adiabatic
pumping. In order to test the experimental feasibility of this approach we
consider the effect of charge noise and the deformations of the optimal pulse
shapes on the accuracy of the pump. Charge noise is assumed to be induced by
random background charges in the substrate, responsible for the observed 1/f
noise. Inaccuracies in the pulse shaping are described by assuming a finite
bandwidth for the pulse generator. In realistic cases the error increases at
most of one order of magnitude as compared to the optimal case. Our results are
promising for the realization of accurate and fast superconducting pumps.Comment: 9 pages, 10 figure
Optimized single-qubit gates for Josephson phase qubits
In a Josephson phase qubit the coherent manipulations of the computational
states are achieved by modulating an applied ac current, typically in the
microwave range. In this work we show that it is possible to find optimal
modulations of the bias current to achieve high-fidelity gates. We apply
quantum optimal control theory to determine the form of the pulses and study in
details the case of a NOT-gate. To test the efficiency of the optimized pulses
in an experimental setup, we also address the effect of possible imperfections
in the pulses shapes, the role of off-resonance elements in the Hamiltonian,
and the effect of capacitive interaction with a second qubit.Comment: 10 pages, 13 figure
Optimization of Junction and Bias Parameters in readout of Phase Qubit
The exact numerical solution of the nonlinear Ginzburg-Landau equation for
Josephson junctions is obtained, from which the nontrivial current density and
effective potential of the Josephson junction are accurately found. Tunneling
probabilities of the calculated bound states in the resulting potential well
are computed. The effects of junction and bias parameters such as thickness of
the insulating barrier, cross sectional area, bias current and magnetic field
are fully investigated using a successive perturbation approach. We define and
compute figures of merit for achieving optimal operation of phase qubits and
measurement of states. Particularly, it is predicted that Josephson junctions
with thicker barriers yield better performance in measurement of the phase
qubit. The proportion of other parameters is also studied and discussed for the
right situation of the setup. Results are in complete agreement with reported
experimental data
Large expert-curated database for benchmarking document similarity detection in biomedical literature search
Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe
Acoustic diffraction by multiple two-dimensional objects; its calculation using an approximate integral method
Presented at the 125th Meeting of the Acoustical Society of America, held in Ottawa, Ont., CanadaPeer reviewed: NoNRC publication: Ye
Vitamin D3 affects mitochondrial biogenesis through mitogen-activated protein kinase in polycystic ovary syndrome mouse model
Polycystic ovarian syndrome (PCOS) is a disorder characterized by oligomenorrhea, anovulation, and hyperandrogenism. Altered mitochondrial biogenesis can result in hyperandrogenism. The goal of this study was to examine the effect of vitamin D3 on mitochondrial biogenesis of the granulosa cells in the PCOS-induced mouse model. Vitamin D3 applies its effect via the mitogen-activated pathway kinase-extracellular signal-regulated kinases (MAPK-ERK1/2) pathway. The PCOS mouse model was induced by the injection of dehydroepiandrosterone (DHEA). Isolated granulosa cells were subsequently treated with vitamin D3, MAPK activator, and MAPK inhibitor. Gene expression levels were measured using real-time polymerase chain reaction. MAPK proteins were investigated by western blot analysis. We also determined reactive oxygen species (ROS) levels with 2�, 7�-dichlorofluorescein diacetate. Mitochondrial membrane potential (mtMP) was also measured by TMJC1. Mitochondrial biogenesis (peroxisome proliferator-activated receptor gamma coactivator 1-α and nuclear respiratory factor), antioxidant (superoxide dismutase, glutathione peroxidase, and catalase), and antiapoptotic (B-cell lymphoma-2) genes were upregulated in the PCOS mice that treated with vitamin D3 compared with the PCOS mice without any treatment. Vitamin D3 and MAPK activator-treated groups also reduced ROS levels compared with the nontreated PCOS group. In summary, vitamin D3 and MAPK activator increased the levels of mitochondrial biogenesis, MAPK pathway, and mtMP markers, while concomitantly decreased ROS levels in granulosa cells of the PCOS-induced mice. This study suggests that vitamin D3 may improve mitochondrial biogenesis through stimulation of the MAPK pathway in cultured granulosa cells of DHEA-induced PCOS mice which yet to be investigated. © 2020 Wiley Periodicals, Inc