2,969 research outputs found
On compression rate of quantum autoencoders: Control design, numerical and experimental realization
Quantum autoencoders which aim at compressing quantum information in a
low-dimensional latent space lie in the heart of automatic data compression in
the field of quantum information. In this paper, we establish an upper bound of
the compression rate for a given quantum autoencoder and present a learning
control approach for training the autoencoder to achieve the maximal
compression rate. The upper bound of the compression rate is theoretically
proven using eigen-decomposition and matrix differentiation, which is
determined by the eigenvalues of the density matrix representation of the input
states. Numerical results on 2-qubit and 3-qubit systems are presented to
demonstrate how to train the quantum autoencoder to achieve the theoretically
maximal compression, and the training performance using different machine
learning algorithms is compared. Experimental results of a quantum autoencoder
using quantum optical systems are illustrated for compressing two 2-qubit
states into two 1-qubit states
Quantum and Classical Magnetoresistance in Ambipolar Topological Insulator Transistors with Gate-tunable Bulk and Surface Conduction
Weak antilocalization (WAL) and linear magnetoresistance (LMR) are two most commonly observed magnetoresistance (MR) phenomena in topological insulators (TIs) and often attributed to the Dirac topological surface states (TSS). However, ambiguities exist because these phenomena could also come from bulk states (often carrying significant conduction in many TIs) and are observable even in non-TI materials. Here, we demonstrate back-gated ambipolar TI field-effect transistors in (Bi0.04Sb0.96)(2)Te-3 thin films grown by molecular beam epitaxy on SrTiO3(111), exhibiting a large carrier density tunability (by nearly 2 orders of magnitude) and a metal-insulator transition in the bulk (allowing switching off the bulk conduction). Tuning the Fermi level from bulk band to TSS strongly enhances both the WAL (increasing the number of quantum coherent channels from one to peak around two) and LMR (increasing its slope by up to 10 times). The SS-enhanced LMR is accompanied by a strongly nonlinear Hall effect, suggesting important roles of charge inhomogeneity (and a related classical LMR), although existing models of LMR cannot capture all aspects of our data. Our systematic gate and temperature dependent magnetotransport studies provide deeper insights into the nature of both MR phenomena and reveal differences between bulk and TSS transport in TI related materials
Totally thoracoscopic closure of ventricular septal defect without a robotically assisted surgical system: A summary of 119 cases
ObjectivesTo summarize the clinical outcomes of totally thoracoscopic closure of a ventricular septal defect (VSD).MethodsTotally thoracoscopic VSD closure was performed in 119 patients (66 boys; mean age, 7.1 ± 3.6 years). An additional 35 patients undergoing open-chest VSD closure were selected as a control group. Using 3 port incisions in the right chest, pericardiotomy, bicaval occlusion, atriotomy, and VSD closure were performed by thoracoscopy without the aid of a robotically assisted surgical system.ResultsCardiopulmonary bypass and aortic crossclamp times were 42.2 ± 9.8 and 32.5 ± 7.3 minutes, respectively. There were no deaths but 1 patient required insertion of a permanent pacemaker as a result of postoperative atrioventricular conduction block. The length of stay in the intensive care unit (11.0 ± 2.6 vs 22.9 ± 4.9 hours, P < .01) or postoperative hospital stay (4.2 ± 1.1 vs 6.6 ± 2.1 days, P < .03) in the thoracoscopic group were shorter than in the control group. The percentage of patients who required postoperative opioid analgesics in the thoracoscopic group was lower than in the control group (31.9% vs 74.2%, P < .001). Rate of blood transfusion during the operation (17.6% vs 65.7%, P = .001) and the postoperative use of opioid analgesics (31.9% vs 74.3%, P = .003) in the thoracoscopic group was lower than in the control group. Transesophageal echocardiographic analysis 4.6 ± 2.3 months after the operation showed complete closure of the defect.ConclusionsTotally thoracoscopic closure of VSD through a 3-port entry was safe and effective
Dark information in black hole with mimetic dark matter
It has been shown that the nonthermal spectrum of Hawking radiation will lead
to information-carrying correlations between emitted particles in the
radiation. The mutual information carried by such correlations can not be
locally observed and hence is dark. With dark information, the black hole
information is conserved. In this paper, we look for the spherically symmetric
black hole solution in the background of dark matter in mimetic gravity and
investigate the radiation spectrum and dark information of the black hole. The
black hole has a similar spacetime structure to the Schwarzschild case, while
its horizon radius is decreased by the dark matter. By using the statistical
mechanical method, the nonthermal radiation spectrum is calculated. This
radiation spectrum is very different from the Schwarzschild case at its last
stage because of the effect of the dark matter. The mimetic dark matter reduces
the lifetime of the black hole but increases the dark information of the
Hawking radiation.Comment: 12 pages, 6 figures, references adde
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