Search

In the present work, we investigate the gravitational lensing effects of two quantum-modified black hole models recently proposed in effective quantum gravity. The light deflection angles in both the weak field limit and the strong field limit are calculated. Furthermore, we use the data of the supermassive black holes SgrA* and M87* and calculate the lensing observables in the strong field limit. We find that the quantum parameter plays a role analogous to the electric charge in the weak gravitational lensing, whereas in the strong field limit, the effect of the quantum parameter on the deflection angle, the angular separation and the relative magnification is opposite to that of the electric charge, the scalar charge and the quantum parameters in some gravity theories. The results indicate the discrepancies between the classical black holes and the two quantum-modified black hole models that depend on the quantum correction, making them a valuable tool for differentiating between these black hole models.

Recently, an interesting \textit{doppelg\"ange} black hole solution is obtained in the string-inspired Euler-Heisenberg theory, where the black holes have the same radii but share different charges. We found, however, they possess different ISCOs and photon spheres, and hence affect their shadow images. In this work, we investigate the optical appearances, illuminated by an optically and geometrically thin disk, are investigated, of such black hole. One finds that doppelg\"ange black holes have different optical appearances. Even the horizon radii are the same, the size of shadows are not equal. Furthermore, we found that the large magnetic charge $Q_m$ black holes give rise to novel shadow images that the usual bright rings inside shadow are not clear, The optical appearances illuminated by spherically accretions are also examined, and it can also identify two doppelg\"ange black holes., Comment: 20 pages, 13 figures, some references added

In this paper, we propose a fully nonlinear mechanism for obtaining scalarized black holes in Einstein-scalar-Gauss-Bonnet (EsGB) gravity which is beyond the spontaneous scalarization. Introducing three coupling functions $f(\varphi)$ satisfying $f''(0) = 0$, we find that Schwarzschild black hole is linearly stable against scalar perturbation, whereas it is unstable against nonlinear scalar perturbation if the coupling function includes term higher than $\varphi^6$. For a specific choice of coupling function $f(\varphi)=\alpha(\varphi^4-\beta\varphi^6)$, we obtain new black holes with scalar hair in the EsGB gravity. In this case, the coupling parameter $\alpha$ plays a major role in making different nonlinear scalarized black holes, while the other parameter $\beta$ plays a supplementary role. Furthermore, we study thermodynamic aspects of these scalarized black holes and prove the first-law of thermodynamics., Comment: 14 pages, 6 figures

Achieving precise preparation of quantum many-body states is crucial for the practical implementation of quantum computation and quantum simulation. However, the inherent challenges posed by unavoidable excitations at critical points during quench processes necessitate careful design of control fields. In this work, we introduce a promising and versatile dynamic control neural network tailored to optimize control fields. We address the problem of suppressing defect density and enhancing cat-state fidelity during the passage across the critical point in the quantum Ising model. Our method facilitates seamless transitions between different objective functions by adjusting the {optimization strategy}. In comparison to gradient-based power-law quench methods, our approach demonstrates significant advantages for both small system sizes and long-term evolutions. We provide a detailed analysis of the specific forms of control fields and summarize common features for experimental implementation. Furthermore, numerical simulations demonstrate the robustness of our proposal against random noise and spin number fluctuations. The optimized defect density and cat-state fidelity exhibit a transition at a critical ratio of the quench duration to the system size, coinciding with the quantum speed limit for quantum evolution., Comment: 14 pages, 9 figures; Accepted in Phys. Rev. A

We investigate the tachyonic instability of Kerr-Newman (KN) black hole with a rotation parameter $a$ in the Einstein-Chern-Simons-scalar theory coupled with a quadratic massive scalar field. This instability analysis corresponds to exploring the onset of spontaneous scalarization for KN black holes. First, we find no $a$-bound for $\alpha<0$ case by considering (1+1)-dimensional analytical method. A direct numerical method is adopted to explore (2+1)-dimensional time evolution of a massive scalar perturbation with positive and negative $\alpha$ to obtain threshold curves numerically. We obtain threshold curves $\alpha_{\rm th}(a)$ of tachyonic instability for positive $\alpha$ without any $a$-bounds. We expect to find the same threshold curves $\alpha_{\rm th}(a)$ of tachyonic instability for negative $\alpha$ without any $a$-bound because its linearized scalar theory is invariant under the transformation of $\alpha\to -\alpha $ and $\theta\to -\theta$. In addition, it is found that the scalar mass term suppresses tachyonic instability of KN black holes., Comment: 18 pages, 4 figures, minor changes

Quantum control plays an irreplaceable role in practical use of quantum computers. However, some challenges have to be overcome to find more suitable and diverse control parameters. We propose a promising and generalizable average-fidelity-based machine-learning-inspired method to optimize the control parameters, in which a neural network with periodic feature enhancement is used as an ansatz. In the implementation of a single-qubit gate by cat-state nonadiabatic geometric quantum computation via reverse engineering, compared with the control parameters in the simple form of a trigonometric function, our approach can yield significantly higher-fidelity ($>99.99\%$) phase gates, such as the $\pi / 8$ gate (T gate). Single-qubit gates are robust against systematic noise, additive white Gaussian noise and decoherence. We numerically demonstrate that the neural network possesses the ability to expand the model space. With the help of our optimization, we provide a feasible way to implement cascaded multi-qubit gates with high quality in a bosonic system. Therefore, the machine-learning-inspired method may be feasible in quantum optimal control of nonadiabatic geometric quantum computation., Comment: 12 pages, 8 figures

The Homotopy Analysis Method (HAM) is a useful method to derive analytical approximate solutions of black holes in modified gravity theories. In this paper, we study the Einstein-Weyl gravity coupled with Maxwell field, and obtain analytical approximation solutions for charged black holes by using the HAM. It is found that the analytical approximate solutions are sufficiently accurate in the entire spacetime outside the black hole's event horizon, and also consistent with numerical ones for charged black holes in the Einstein-Maxwell-Weyl gravity., Comment: 17 pages, 6 figures. arXiv admin note: text overlap with arXiv:2308.03506

In this paper, we discuss a fully nonlinear mechanism for the formation of scalarized rotating black holes in Einstein-scalar-Gauss-Bonnet gravity, where Kerr black holes are linearly stable, but unstable against nonlinear scalar perturbations. With the help of the pseudospectral method, we obtain a spectrum of nonlinearly scalarized rotating black hole solutions with multiple scalarized branches. Moreover, we investigate the thermodynamic properties of nonlinearly scalarized rotating black holes and find the phase transition between Kerr and these scalarized black holes., Comment: 23 pages, 8 figures and 2 tables

The spontaneous scalarization of Schwarzscild-AdS is investigated in the Einstein-scalar-Gauss--Bonnet (ESGB) theory. Firstly, we construct scalarized AdS black holes numerically. Secondly, making use of the homotopy analysis method (HAM), we obtain analytical approximate solutions for scalarized AdS black holes in the ESGB theory. It is found that scalarized AdS black holes constructed numerically are consistent with analytical approximate solutions in the whole space., Comment: 20 pages, 5 figures

Coherently driven semiconductor quantum dots are one of the most promising platforms for non-classical light sources and quantum logic gates which form the foundation of photonic quantum technologies. However, to date, coherent manipulation of single charge carriers in quantum dots is limited mainly to their lowest orbital states. Ultrafast coherent control of high-orbital states is obstructed by the demand for tunable terahertz pulses. To break this constraint, we demonstrate an all-optical method to control high-orbital states of a hole via stimulated Auger process. The coherent nature of the Auger process is proved by Rabi oscillation and Ramsey interference. Harnessing this coherence further enables the investigation of single-hole relaxation mechanism. A hole relaxation time of 161 ps is observed and attributed to the phonon bottleneck effect. Our work opens new possibilities for understanding the fundamental properties of high-orbital states in quantum emitters and developing new types of orbital-based quantum photonic devices., Comment: Manuscript with 14 pages and 6 figures plus supplementary Information comprising 15 pages and 14 figures. Nature Nanotechnology (24 July 2023)

It was confirmed that the negative modes of the Euclidean section for asymptotically flat black holes reveal the thermodynamic instability of these black holes in the grand canonical ensemble (GCE). These include Schwarzschild, Reissner-Nordstr\"{o}m, Kerr, and Kerr-Newman black holes. In this work, we develop the relation between thermodynamic instability in the GCE and tachyonic instability for asymptotically flat black holes, where the latter is the onset for obtaining black holes with scalar hair. This implies that the tachyonic instability of black holes when introducing scalar coupling to the Gauss-Bonnet term or Maxwell term reflects thermodynamic instability of these black holes in the GCE. We go on further to consider the Schwarzschild-AdS black hole., Comment: 19 pages, 5 figures

We investigate the tachyonic instability of Kerr-Newman (KN) black holes in the Einstein-Maxwell-scalar (EMS) theory with a positive coupling parameter $\alpha$. This corresponds to exploring the onset of spontaneous scalarization for KN black holes. For this purpose, we use the hyperboloidal foliation method (HFM) to solve the linearized scalar equation numerically. We obtain a 3D graph [$\log_{10}\alpha(a,Q)$] which indicates the onset surface for spontaneous scalarization of KN black holes in the EMS theory. We find that there is no lower bound on the rotational parameter $a$, but its upper bound is given by $M^2-Q^2 \ge a^2$. Also, we confirm that the high rotation enhances spontaneous scalarization of KN black holes in the EMS theory., Comment: 21 pages, 6 figures, Version accepted for publication in PRD. arXiv admin note: text overlap with arXiv:2206.11587

The motion of quantum particles homogeneously constrained to a curved surface is affected by a curvature induced geometric potential. Here, we consider the case of inhomogeneous confinement and derive the effective Hamiltonian by extending thin-layer procedure, where an extra effective potential appears. This effective potential is relevant to the ground state energy perpendicular to the surface and the morphology of the confining potential. Tiny changes in the thickness are envisioned to induce considerable magnitude of the effective potential. To demonstrate the impact of the inhomogeneity, we apply our method to investigate the coherent transport on a cylindrical surface where a confining potential with two helical ditches is imposed. Numerical analysis reveals that the inhomogeneity of the confinement significantly changes the transport properties. This study develops the method for low-dimensional constrained systems and exhibits the possibility of new degree of control for waveguiding in nanostructures.

In this paper, we consider the tachyonic instability of Kerr-Newman (KN) black holes in the Einstein-Maxwell-scalar (EMS) theory with nonminimal negative scalar coupling to Maxwell term, and then obtain a bound $(\frac{a}{r_+}\geq0.4142)$ for spin parameter $a$ of KN black hole in the limit of coupling constant $\alpha\rightarrow-\infty$ by using analytical method. In addition, we perform a $(2+1)$-dimensional time evolution of linearized scalar field perturbation on the KN black hole background by implementing the hyperboloidal foliation method numerically in the EMS theory. It recovers the \textit{spontaneous scalarization} phenomenon for KN black hole in some certain regions of the parameter spaces. We further plot corresponding threshold curves $\alpha(a)$ which describe a boundary between bald KN black holes and scalarized spinning black holes in the EMS theory., Comment: 23 pages, 6 figures

We study echoes of free massless scalar from dyonic black holes in Einstein-Maxwell gravity extended with the quasi-topological electromagnetic term. These asymptotically-flat black holes all satisfy the dominant energy condition. We find that for suitable parameters, the effective potential can have double peaks and consequently echoes of quasinormal modes arise. In general the echo frequency associated with the initial wave packet released inside the two peaks is about twice the frequency of the one released outside., Comment: Latex, 20 pages, 29 plots grouped into 11 figures