Spin-Orbit Interaction Enabled High-Fidelity Two-Qubit Gates

We study the implications of spin-orbit interaction (SOI) for two-qubit gates (TQGs) in semiconductor spin qubit platforms. The exchange interaction governing qubit pairs is anisotropic under SOI, posing a problem for conventional TQGs derived under the Heisenberg exchange. After developing a concise form of the effective two-qubit Hamiltonian under SOI, we use it to derive properties of rotating-frame evolution. Two main observations are made. First, in contrary to past belief, we find that an appropriate amount of SOI can significantly enhance the controlled-phase gate fidelity compared to the no-SOI case. Second, SOI enables novel two-qubit dynamics, that are conventionally inaccessible through DC evolution, such as the reflection gate and the controlled-not gate

Coupling of quantum-dot states via elastic-cotunneling and crossed Andreev reflection in a minimal Kitaev chain

Recently, exciting progress has been made in using the superconducting nanowires coupled to gate-defined quantum dots (QDs) to mimic the Kiteav chain and realize the Majorana-bound states via a poor man's route. The essential ingredient is to balance the interdot elastic-cotunneling (ECT) and crossed Andreev reflection (CAR). As theoretically proposed, this can be mediated by the Andreev bound states (ABSs) formed in the superconducting nanowires. However, most of the gate-tuning asymmetric features observed in experiments can not be captured using the current theoretical models. To address this insufficiency, here, we consider a full model that explicitly includes all the details of both the QD states and the ABSs. Remarkable agreement is found with the recent experimental observations, where our model correctly reveals the gate-tuning asymmetry in ECTs and by which the average QD state energy can also be extracted. In contrast, CARs do not depend on the tuning of QD states. Moreover, armed with the tunability of ECTs and CARs with QD states, we also predict a controllable anisotropic superexchange interaction between electron spins in the two separated QDs

Two types of generalized integrable decompositions and new solitary-wave solutions for the modified Kadomtsev-Petviashvili equation with symbolic computation

The modified Kadomtsev-Petviashvili (mKP) equation is shown in this paper to be decomposable into the first two soliton equations of the 2N-coupled Chen-Lee-Liu and Kaup-Newell hierarchies by respectively nonlinearizing two sets of symmetry Lax pairs. In these two cases, the decomposed (1+1)-dimensional nonlinear systems both have a couple of different Lax representations, which means that there are two linear systems associated with the mKP equation under the same constraint between the potential and eigenfunctions. For each Lax representation of the decomposed (1+1)-dimensional nonlinear systems, the corresponding Darboux transformation is further constructed such that a series of explicit solutions of the mKP equation can be recursively generated with the assistance of symbolic computation. In illustration, four new families of solitary-wave solutions are presented and the relevant stability is analyzed.Comment: 23 page

VEGF attenuates development from cardiac hypertrophy to heart failure after aortic stenosis through mitochondrial mediated apoptosis and cardiomyocyte proliferation

<p>Abstract</p> <p>Background</p> <p>Aortic stenosis (AS) affects 3 percent of persons older than 65 years and leads to greater morbidity and mortality than other cardiac valve diseases. Surgery with aortic valve replacement (AVR) for severe symptomatic AS is currently the only treatment option. Unfortunately, in patients with poor ventricular function, the mortality and long-term outcome is unsatisfied, and only a minority of these patients could bear surgery. Our previous studies demonstrated that vascular endothelial growth factor (VEGF) protects cardiac function in myocardial infarction model through classic VEGF-PI3k-Akt and unclear mitochondrial anti-apoptosis pathways; promoting cardiomyocyte (CM) proliferation as well. The present study was designed to test whether pre-operative treatment with VEGF improves AS-induced cardiac dysfunction, to be better suitable for AVR, and its potential mechanism.</p> <p>Methods</p> <p>Adult male mice were subjected to AS or sham operation. Two weeks later, adenoviral VEGF (Ad-VEGF), enhanced green fluorescence protein (Ad-EGFP, as a parallel control) or saline was injected into left ventricle free wall. Two weeks after delivery, all mice were measured by echocardiography and harvested for further detection.</p> <p>Results</p> <p>AS for four weeks caused cardiac hypertrophy and left ventricular dysfunction. VEGF treatment increased capillary density, protected mitochondrial function, reduced CMs apoptosis, promoted CMs proliferation and eventually preserved cardiac function.</p> <p>Conclusions</p> <p>Our findings indicate that VEGF could repair AS-induced transition from compensatory cardiac hypertrophy to heart failure.</p

Quantifying immediate price impact of trades based on the kk-shell decomposition of stock trading networks

Traders in a stock market exchange stock shares and form a stock trading network. Trades at different positions of the stock trading network may contain different information. We construct stock trading networks based on the limit order book data and classify traders into $k$ classes using the $k$-shell decomposition method. We investigate the influences of trading behaviors on the price impact by comparing a closed national market (A-shares) with an international market (B-shares), individuals and institutions, partially filled and filled trades, buyer-initiated and seller-initiated trades, and trades at different positions of a trading network. Institutional traders professionally use some trading strategies to reduce the price impact and individuals at the same positions in the trading network have a higher price impact than institutions. We also find that trades in the core have higher price impacts than those in the peripheral shell.Comment: 6 pages including 3 figures and 1 tabl

Topological phase transition in a narrow bandgap semiconductor nanolayer

Narrow bandgap semiconductor nanostructures have been explored for realization of topological superconducting quantum devices in which Majorana states can be created and employed for constructing topological qubits. However, a prerequisite to achieve the topological phase transition in these nanostructures is application of a magnetic field, which could complicate the technology development towards topological quantum computing. Here we demonstrate that a topological phase transition can be achieved in a narrow bandgap semiconductor nanolayer under application of a perpendicular electric field. Based on full band structure calculations, it is shown that the topological phase transition occurs at an electric-field induced band inversion and is accompanied by a sharp change of the $\mathbb{Z}_{2}$ invariant at the critical field. We also demonstrate that the nontrivial topological phase is manifested by the quantum spin Hall edge states in a band-inverted nanolayer Hall-bar structure. We present the phase diagram of the nanolayer in the space of layer thickness and electric field strength, and discuss the optimal conditions to achieve a large topological bandgap in the electric-field induced topological phase of a semiconductor nanolayer.Comment: 6 pages, 5 figure

Enhanced cancer therapy with cold-controlled drug release and photothermal warming enabled by one nanoplatform

Stimuli-responsive nanoparticles hold great promise for drug delivery to improve the safety and efficacy of cancer therapy. One of the most investigated stimuli-responsive strategies is to induce drug release by heating with laser, ultrasound, or electromagnetic field. More recently, cryosurgery (also called cryotherapy and cryoablation), destruction of diseased tissues by first cooling/freezing and then warming back, has been used to treat various diseases including cancer in the clinic. Here we developed a cold-responsive nanoparticle for controlled drug release as a result of the irreversible disassembly of the nanoparticle when cooled to below ∼10 °C. Furthermore, this nanoparticle can be used to generate localized heating under near infrared (NIR) laser irradiation, which can facilitate the warming process after cooling/freezing during cryosurgery. Indeed, the combination of this cold-responsive nanoparticle with ice cooling and NIR laser irradiation can greatly augment cancer destruction both in vitro and in vivo with no evident systemic toxicity

Enhanced Orbital Degeneracy in Momentum Space for LaOFeAs

The Fermi surfaces (FS) of LaOFeAs (in $k_z$=0 plane) consist of two hole-type circles around $\Gamma$ point, which do not touch each other, and two electron-type co-centered ellipses around M point, which are degenerate along the M-X line. By first-principles calculations, here we show that additional degeneracy exists for the two electron-type FS, and the crucial role of F-doping and pressure is to enhance this orbital degeneracy. It is suggested that the inter-orbital fluctuation is the key point to understand the unconventional superconductivity in these materials.Comment: 4 pages, 5 figure

Scattering description of edge states in Aharonov-Bohm triangle chains

Scattering theory has been suggested as a convenient method to identify topological phases of matter, in particular of disordered systems for which the Bloch band-theory approach is inapplicable. Here we examine this idea, employing as a benchmark a one-dimensional triangle chain whose versatility yields a scattering matrix that ``flows" in parameter space among several members of the topology classification scheme. Our results show that the reflection amplitudes (from both ends of a sufficiently long chain) do indicate the appearance of edge states in {\it all} (topological and non-topological) cases. For the topological cases, the transmission has a peak at the topological phase transition, which happens at the Fermi energy. A peak still exists as one moves into the non-topological `trivial' regions, in which another transmission peak may occur at nonzero energy, at which a relevant edge state appears in the isolated chain. For finite chains, the peak in the transmission strongly depends on their coupling of the leads, and {\it not} on the phase transition of the isolated chain. In any case, {\it the appearance of a peak in the transmission is not sufficient to conclude that the system undergoes a topological phase transition.