2,204 research outputs found
High fidelity all-optical control of quantum dot spins: detailed study of the adiabatic approach
Confined electron spins are preferred candidates for embodying quantum
information in the solid state. A popular idea is the use of optical excitation
to achieve the ``best of both worlds'', i.e. marrying the long spin decoherence
times with rapid gating. Here we study an all-optical adiabatic approach to
generating single qubit phase gates. We find that such a gate can be extremely
robust against the combined effect of all principal sources of decoherence,
with an achievable fidelity of 0.999 even at finite temperature. Crucially this
performance can be obtained with only a small time cost: the adiabatic gate
duration is within about an order of magnitude of a simple dynamic
implementation. An experimental verification of these predictions is
immediately feasible with only modest resources
A generalized multi-polaron expansion for the spin-boson model: Environmental entanglement and the biased two-state system
We develop a systematic variational coherent state expansion for the
many-body ground state of the spin-boson model, in which a quantum two-level
system is coupled to a continuum of harmonic oscillators. Energetic constraints
at the heart of this technique are rationalized in terms of polarons
(displacements of the bath states in agreement with classical expectations) and
antipolarons (counter-displacements due to quantum tunneling effects). We
present a comprehensive study of the ground state two-level system population
and coherence as a function of tunneling amplitude, dissipation strength, and
bias (akin to asymmetry of the double well potential defining the two-state
system). The entanglement among the different environmental modes is
investigated by looking at spectroscopic signatures of the bipartite
entanglement entropy between a given environmental mode and all the other
modes. We observe a drastic change in behavior of this entropy for increasing
dissipation, indicative of the entangled nature of the environmental states. In
addition, the entropy spreads over a large energy range at strong dissipation,
a testimony to the wide entanglement window characterizing the underlying Kondo
state. Finally, comparisons to accurate numerical renormalization group
calculations and to the exact Bethe Ansatz solution of the model demonstrate
the rapid convergence of our variationally-optimized multi-polaron expansion,
suggesting that it should also be a useful tool for dissipative models of
greater complexity, as relevant for numerous systems of interest in quantum
physics and chemistry.Comment: 17 pages, 14 figure
Stabilizing Spin Coherence Through Environmental Entanglement in Strongly Dissipative Quantum Systems
The key feature of a quantum spin coupled to a harmonic bath---a model
dissipative quantum system---is competition between oscillator potential energy
and spin tunneling rate. We show that these opposing tendencies cause
environmental entanglement through superpositions of adiabatic and
antiadiabatic oscillator states, which then stabilizes the spin coherence
against strong dissipation. This insight motivates a fast-converging
variational coherent-state expansion for the many-body ground state of the
spin-boson model, which we substantiate via numerical quantum tomography.Comment: 5 pages, 3 figures, supplementary file attached. This article
supersedes arXiv:1301.743
A general approach to quantum dynamics using a variational master equation: Application to phonon-damped Rabi rotations in quantum dots
We develop a versatile master equation approach to describe the
non-equilibrium dynamics of a two-level system in contact with a bosonic
environment, which allows for the exploration of a wide range of parameter
regimes within a single formalism. As an experimentally relevant example, we
apply this technique to the study of excitonic Rabi rotations in a driven
quantum dot, and compare its predictions to the numerical Feynman integral
approach. We find excellent agreement between the two methods across a
generally difficult range of parameters. In particular, the variational master
equation technique captures effects usually considered to be non-perturbative,
such as multi-phonon processes and bath-induced driving renormalisation, and
can give reliable results even in regimes in which previous master equation
approaches fail.Comment: 5 pages, 2 figures. Published version, revised title, minor changes
to the tex
A Reliable Reinforcement Learning for Resource Allocation in Uplink NOMA-URLLC Networks
In this paper, we propose a deep state-action-reward-state-action (SARSA) λ learning approach for optimising the uplink resource allocation in non-orthogonal multiple access (NOMA) aided ultra-reliable low-latency communication (URLLC). To reduce the mean decoding error probability in time-varying network environments, this work designs a reliable learning algorithm for providing a long-term resource allocation, where the reward feedback is based on the instantaneous network performance. With the aid of the proposed algorithm, this paper addresses three main challenges of the reliable resource sharing in NOMA-URLLC networks: 1) user clustering; 2) Instantaneous feedback system; and 3) Optimal resource allocation. All of these designs interact with the considered communication environment. Lastly, we compare the performance of the proposed algorithm with conventional Q-learning and SARSA Q-learning algorithms. The simulation outcomes show that: 1) Compared with the traditional Q learning algorithms, the proposed solution is able to converges within 200 episodes for providing as low as 10-2 long-term mean error; 2) NOMA assisted URLLC outperforms traditional OMA systems in terms of decoding error probabilities; and 3) The proposed feedback system is efficient for the long-term learning process
Optimasi Produk Plastik pendekatan Taguchi Mixed Level pada Faktor Interaksi Injeksi Molding
Penelitian parameter injeksi molding diperlukan untuk meminimalkan produk cacat penyusutan (shrinkage). Diharapkan perbaikan penelitian yang mengintegrasikan metode Taguchi untuk mengoptimalkan parameter injeksi serta interaksi yang mungkin terjadi. Berdasarkan uraian tersebut permasalahan yang dibahas adalah bagaimana mendapatkan parameter terbaik untuk optimasi produk plastik menggunakan pendekatan taguchi mixed level dengan 6 faktor faktor interaksi injeksi molding dan variasi level. Metode Taguchi merupakan suatu metode pengendalian kualitas sebelum proses berlangsung, orthogonal array yang akan digunakan L18(2135) sesuai dengan jumlah faktor sebanyak 6 dan menggunakan mixed level. Variabel respon shrinkage diukur dari plastik tray yang terbuat dari campuran polimer atau poliblend. Faktor yang digunakan yaitu dengan memvariasikan injection speed (kecepatan injeksi), melting temperature (suhu leleh), injection pressure (tekanan injeksi), holding pressure (tekanan penahanan), holding time (waktu penahanan) dan cooling time (waktu pendinginan). Parameter optimal tanpa efek interaksi dengan kondisi optimum adalah kecepatan injeksi (90 %rpm), suhu leleh (240 °C), tekanan injeksi (110 bar), tekanan penahanan (96 bar), waktu penahanan (5 detik), dan pendinginan waktu (10 detik). Parameter optimal dengan efek interaksi kondisi optimum yaitu suhu leleh (240 ° C), tekanan injeksi (110 bar), tekanan penahanan (80 bar), waktu penahanan (5 detik), dan waktu pendinginan (10 detik). Kontribusi parameter dengan interaksi adalah suhu leleh (56,65%), interaksi suhu leleh dan tekanan injeksi (15,75%), waktu pendinginan (11,12%), dan kekuatan tekanan (7,83%)
Creating excitonic entanglement in quantum dots through the optical Stark effect
We show that two initially non-resonant quantum dots may be brought into
resonance by the application of a single detuned laser. This allows for control
of the inter-dot interactions and the generation of highly entangled excitonic
states on the picosecond timescale. Along with arbitrary single qubit
manipulations, this system would be sufficient for the demonstration of a
prototype excitonic quantum computer.Comment: 4 pages, 3 figures; published version, figure 3 improved, corrections
to RWA derive
Resource Allocation in Uplink NOMA-IoT Networks: A Reinforcement-Learning Approach
Non-orthogonal multiple access (NOMA) exploits the potential of the power domain to enhance the connectivity for the Internet of Things (IoT). Due to time-varying communication channels, dynamic user clustering is a promising method to increase the throughput of NOMA-IoT networks. This paper develops an intelligent resource allocation scheme for uplink NOMA-IoT communications. To maximise the average performance of sum rates, this work designs an efficient optimization approach based on two reinforcement learning algorithms, namely deep reinforcement learning (DRL) and SARSA-learning. For light traffic, SARSA-learning is used to explore the safest resource allocation policy with low cost. For heavy traffic, DRL is used to handle traffic-introduced huge variables. With the aid of the considered approach, this work addresses two main problems of fair resource allocation in NOMA techniques: 1) allocating users dynamically and 2) balancing resource blocks and network traffic. We analytically demonstrate that the rate of convergence is inversely proportional to network sizes. Numerical results show that: 1) Compared with the optimal benchmark scheme, the proposed DRL and SARSA-learning algorithms have lower complexity with acceptable accuracy and 2) NOMA-enabled IoT networks outperform the conventional orthogonal multiple access based IoT networks in terms of system throughput
Clinics in diagnostic imaging (102)
A 19-year-old man presented with cough and haemoptysis of ten days duration. He also had mild right hypochondrial pain. Chest radiograph and computed tomography (CT) showed a rounded soft tissue density opacity with an air crescent sign. CT showed multiple cystic lesions in the liver with a daughter cyst in its lateral wall. Diagnosis of hydatid disease of lung and liver was made. The contents of the liver cyst were aspirated, hypertonic saline instilled, re-aspirated, and absolute alcohol injected. Hydatid disease is endemic in certain parts of the world. Although the lungs and liver are most frequently affected, the disease can arise in any part of the body and should be kept in differential diagnosis whenever a cystic lesion is encountered. Hydatid cysts typically demonstrate characteristic imaging findings, however, the appearances may become complicated due to cyst rupture or secondary infection. Ultrasonography is the imaging modality of choice particularly in hepatic disease. CT best demonstrates cyst wall calcification and cyst infection
In Vitro Antioxidant and In Vivo Hepatoprotective Activity of Leave Extract of Raphanus Sativus in Rats Using CCL4 Model
Background: Raphanus sativus is reported to have a variety of biological activities. This work screened the hepato-protective and antioxidant activity of ethanol (ERS), and aqueous (ARS), extracts of leaves of Raphanus sativus in Carbon tetrachloride (CCl4), model in rats.Material and Methods: The extracts were subjected to antioxidant tests (Total reducing power and Total phenolic content), and preliminary phytochemical screening. A pilot study was done on 100 and 300 mg/kg extracts, form which 300 mg was chosen for further experiments. The albino rats (200-250 grams), were divided into 5 groups of 6 animals each (n=6). There were three control groups comprising of normal control (normal saline -1ml/kg), negative control group (CCl4 1ml/kg in olive oil in a ratio of 1:1 v/v), and positive control group (Silymarin 50mg/kg). The Test drugs were given in a dose of 300 mg/kg for both ERS and ARS extract for 7 days. Biochemical parameters (AST, ALT, Alkaline phosphatase, Total Bilirubin), histo-pathological examination of liver and in vivo antioxidant tests [CAT, GSH and MDA] were done.Results: The phytochemical study showed the presence of flavanoids, terpenoids, alkaloids, saponins and sterols. A dose dependent increase in the oxidative potential was observed in both the extracts with total phenolic content 70.1 and 44.4 GAE/g extract for ERS and ARS respectively. ERS 300mg/kg showed a significant (p<0.001) increase in levels of AST, ALT and alkaline phosphatase as compared to negative control (percentage hepatoprotection =45.3%) while ARS 300 mg/kg (p<.01) group showed 30% hepatoprotection. The GSH (p<0.001) and CAT (p<0.05) in ERS and ARS were significantly increased while MDA levels were decreased (P< 0.01), as compared negative control. The findings were confirmed histo-pathological examination.Conclusion: The ethanol and aqueous extract of Raphanus sativus have partial hepatoprotection against CCl4 toxicity.Key words: Raphanus sativus, hepatoprotection, CCl4, antioxidant
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