Generation of quantum coherence for continuous variables between causally disconnected regions in dilaton spacetime

The quantum entanglement, discord, and coherence dynamics of two spins in the model of a spin coupled to a spin bath through an intermediate spin are studied. The effects of the important physical parameters including the coupling strength of two spins, the interaction strength between the intermediate spin and the spin bath, the number of bath spins and the temperature of the system on quantum coherence and correlation dynamics are discussed in different cases. The frozen quantum discord can be observed whereas coherence does not when the initial state is the Bell-diagonal state. At finite temperature, we find that coherence is more robust than quantum discord, which is better than entanglement, in terms of resisting the influence of environment. Therefore, quantum coherence is more tenacious than quantum correlation as an important resource.

In this work we investigate if the interaction of the Kerr–Taub–NUT spacetime with test scalar and neutrino fields can lead to the destruction of the event horizon. It turns out that both extremal and nearly extremal black holes can be destroyed by scalar and neutrino fields if the initial angular momentum of the spacetime is sufficiently large relative to its mass and NUT charge. This is the first example in which a classical field satisfying the null energy condition can actually destroy an extremal black hole. For scalar fields, the modes that can lead to the destruction of the horizon are restricted to a narrow range due to superradiance. Since superradiance does not occur for neutrino fields, the destruction of the horizon by neutrino fields is generic, and it cannot be fixed by backreaction effects. We also show that the extremal black holes that can be destroyed by scalar fields correspond to naked singularities in the Kerr limit, in accord with the previous results which imply that extremal Kerr black holes cannot be destroyed by scalar test fields.

The theory of nonlinear electrodynamics has got a lot of attentions in recent years. It was shown that Born-Infeld nonlinear electrodynamics is not the only modification of the linear Maxwell's field which keeps the electric field of a charged point particle finite at the origin, and other type of nonlinear Lagrangian such as exponential and logarithmic nonlinear electrodynamics can play the same role. In this paper, we generalize the study on the exponential nonlinear electrodynamics by adding a scalar dilaton field to the action. By suitably choosing the coupling of the matter field to the dilaton field, we vary the action and obtain the corresponding field equations. Then, by making a proper ansatz, we construct a new class of charged dilaton black hole solutions coupled to the exponential nonlinear electrodynamics field in the presence of two Liouville-type potentials for the dilaton field. Due to the presence of the dilaton field, the asymptotic behavior of these solutions are neither flat nor (A)dS. In the limiting case where the nonlinear parameter $\beta^2$ goes to infinity, our solution reduces to the Einstein-Maxwell dilaton black holes. We obtain the mass, temperature, entropy and electric potential of these solutions. We also study the behaviour of the electric field as well as the electric potential of these black holes near the origin. We find that the electric field has a finite value \textit{near} the origin, which is the same as the electric field of Born-Infeld nonlinear electrodynamics, but it can diverge exactly at $r=0$ depending on the model parameters. We also investigate the effects of the dilaton field on the behaviour of the electric field and electric potential. Finally, we check the validity of the first law of black hole thermodynamics on the black hole horizon.

The quantumness of Dirac particles for quantized fields in a dilatonic black hole is estimated by means of quantum channel. A general Bloch vector representation of quantum channel in black hole spacetimes beyond single mode approximation is developed. The nonclassicality of Dirac particles can be measured by the minimization of quantum coherence over all orthonormal basis sets. The quantumness of the channel decreases as the dilaton field increases. The interplay between the external reservoir noise and dilaton black hole on the dynamical behavior of quantum coherence and steerability is investigated in the Pauli basis. The external environment is modeled by a random telegraph noise channel. The monotonous decay of quantum nonlocality occurs in the weak coupling case. The degradation and revival of quantum nonlocality are observed in the strong coupling condition. It is found that quantum fluctuation effects of the external reservoir can protect quantum coherence and steerability from the information loss of the black hole.

The radical departure from classical physics implies quantum coherence, i.e., coherent superposition of eigenstates of Hermitian operators. In resource theory, quantum coherence is a resource for quantum operations. Typically the stochastic phenomenon induces decoherence effects. However, in the present work, we prove that nonunitary evolution leads to the generation of quantum coherence in some cases. Specifically, we consider the neutrino propagation in the dissipative environment, namely in a magnetic field with a stochastic component, and focus on neutrino flavour, spin and spin-flavour oscillations. We present exact analytical results for quantum coherence in neutrino oscillations quantified in terms of the relative entropy. Starting from an initial zero coherence state, we observe persistent oscillations of coherence during the dissipative evolution of an ultra-high energy neutrino in a random interstellar magnetic field. We found that after dissipative evolution, the initial spin-polarized state entirely “thermalizes”, and in the final steady state, the spin-up/down states have the same probabilities. On the other hand, neutrino flavour states also “thermalize”, but the populations of two flavour states do not equate to each other. The initial flavour still dominates in the final steady state.

We test whether static charged dilaton black holes in [Formula: see text] dimensions can be turned into naked singularities by sending in test particles from infinity. We derive that overcharging is possible and generic for both extremal and nearly extremal black holes. Our analysis also implies that nearly extremal charged dilaton black holes can be continuously driven to extremality and beyond, unlike nearly extremal Ban̆ados–Teitelboim–Zanelli, Kerr and Reissner–Nordström black holes which are overspun or overcharged by a discrete jump. Thus, the weak form of the cosmic censorship conjecture and the third law of black hole thermodynamics are both violated in the interaction of charged dilaton black holes in [Formula: see text] dimensions, with test particles. We also derive that there exist no points, where the heat capacity vanishes or diverges in the transition from black holes to naked singularities. The phase transitions that could potentially prevent the formation of naked singularities do not occur.

The dynamic phase transition of charged dilaton black holes is investigated in this paper. The Gibbs free energy landscape is introduced, and the corresponding is calculated for the dilaton black hole. We numerically solve the Fokker-Planck equation constrained by only the reflecting boundary condition. The effects of dilaton gravity on the probabilistic evolution of dilaton black holes are explored. Firstly, the horizon radius difference between a large dilaton black hole and a small dilaton black hole increases with the parameter . Secondly, with increasing , the system needs much more time to achieve a stationary distribution. Finally, the values attained for and vary with . Additionally, by resolving the Fokker-Planck equation constrained by both the reflecting boundary condition and absorbing boundary condition, we investigate the first passage process of dilaton black holes. The initial peak decays more slowly with increasing , which can also be observed via the slowing decay of (the sum of the probability of the black hole system not having completed a first passage by time t). Moreover, the time corresponding to the single peak of the first passage time distribution is found to increase with the parameter . Considering these observations, the dilaton field is found to slow down the dynamic phase transition process between a large black hole and a small black hole.

This study investigates the dynamics of quantum correlations and coherence in an open hybrid superconducting (SC) qubit-cavity system, focusing on quantum discord (QD), entanglement of formation and JS coherence. The results show that the initial cavity state, Ising interactions, qubit-cavity detuning, and SC qubit-cavity couplings significantly affects the quantum behavior of the system. Furthermore, the study highlights that increasing qubit–qubit interaction coupling via Ising interactions and tuning the qubit-cavity detuning have strong effects on quantum correlations, with QD showing greater resilience compared to entanglement, especially in noisy environments. These results highlight the importance of controlling both the initial cavity state and the interaction strengths to optimize quantum correlations and coherence. The insights gained from this study are a valuable contribution to the development of robust quantum systems that improve strategies for SC quantum processors and the broader field of quantum computing.

We considered the behaviour of Dirac fermion modes in the background of Euclidean dilaton black hole with an Abelian Higgs vortex passing through it. Fermions were coupled to the fields due to the superconducting string model. The case of nonextremal and extremal charged black hole in the theory with arbitrary coupling constant between dilaton field and U(1)-gauge field were considered. We elaborated the cases of zero and non-zero Dirac fermion modes. One finds the evidence that the system under consideration can support fermion fields acting like superconducting hair on black hole in the sence that nontrivial spinor field configuration can be carried by Euclidean spherically symmetric charged dilaton black hole. It was revealed that the localization of Dirac fermion modes depended on the cosmic string winding number and the value of black hole surface gravity.

We investigate the dynamics of quantum coherence among multiple diamond nitrogen–vacancy centers (NVCs) coupled to a microsphere whispering-gallery-mode (WGM) cavity under external driving, through numerically simulating the Markovian quantum master equation. We show that quantum coherence (both normal quantum coherence and relative entropy) displays a series of damped oscillations under various experimental situations, which reflects the intricate interplay and competition between the dissipative effects and NVC-WGM coupling. Our results also show that normal quantum coherence is an upper bound for relative entropy. The feasibility of our proposal is supported by currently available experimental techniques.

Using coupled harmonic oscillators model, we numerical analyze the entanglement entropy of massless scalar field in Gafinkle–Horowitz–Strominger (GHS) dilaton spacetime and Gibbons–Maeda (GM) dilaton spacetime. By numerical fitting, we find that the entanglement entropy of the dilaton black holes receive contribution from dilaton charge and is proportional to the area of the event horizon. It is interesting to note that the results of numerical fitting are coincide with ones obtained by using brick wall method and Euclidean path integral approach.

We investigate the interplay between quantum thermodynamics, quantum correlations, and quantum coherence within the framework of the Unruh–DeWitt (UdW) detector model. By analyzing both the steady and dynamical states of various quantum resources-including steerability, entanglement, quantum discord, and coherence-we study how these resources evolve under Markovian and non-Markovian environments. Furthermore, the hierarchical structure relating quantum correlations and quantum coherence is established. We also examine the thermodynamic performance of a quantum heat engine, highlighting the influence of memory effects and classical correlations on heat exchange, work extraction, and efficiency.

In this paper a system consisting of two electron spins has been prepared initially in a singlet state using the chemical compass model is considered. It is assumed that each electron spin interacts symmetrically and/or asymmetrically with its respective private nuclear environment in the presence of an external magnetic field. We discussed the effect of the interaction parameters and the external magnetic field on some quantifiers of quantum correlations as entanglement, coherence, Bell inequality, as well as the steerability inequality. It is shown that within a certain range of external magnetic fields, the quantum coherence and entanglement behave similarly. The Bell and the steerable inequalities predicted a similar behavior for symmetric and asymmetric interactions. Moreover, as one increases the external magnetic field, the lower bounds of both inequalities have improved. The usefulness of using the spin state as quantum channel to teleport a two-qubit system has examined where the Bell inequality could be above its classical bounds by controlling the interaction parameters. It is shown that by tuning the coupling parameters the fidelity of the teleported state exceeds the classical bounds, as well as the long-lived stationary fidelity could be achieved during the interaction time.

Quantum coherence is a fundamental aspect of quantum physics and plays a central role in quantum information science. This essential property of the quantum states could be fragile under the influence of the quantum operations. The extent to which quantum coherence is diminished depends both on the channel and the incoherent basis. Motivated by this, we propose a measure of nonclassicality of a quantum channel as the average quantum coherence of the state space after the channel acts on, minimized over all orthonormal basis sets of the state space. Utilizing the squared $l_1$-norm of coherence for the qubit channels, the minimization can be treated analytically and the proposed measure takes a closed form of expression. If we allow the channels to act locally on a maximally entangled state, the quantum correlation is diminished making the states more classical. We show that the extent to which quantum correlation is preserved under local action of the channel cannot exceed the quantumness of the underlying channel. We further apply our measure to the quantum teleportation protocol and show that a nonzero quantumness for the underlying channel provides a necessary condition to overcome the best classical protocols.

The standard theory of NMR relaxation in liquids (with molecular motion described as a classical Brownian motion, and including intermolecular spin–spin couplings) is re-examined, taking great care not to drop significant contributions from the dipolar coupling between distant molecules. This results in ‘‘modified Bloch–Redfield equations’’ for the spins in a single molecule, valid at all spin temperatures, which contain both the usual relaxation terms and a coupling of each spin with a classical average dipolar field. Delicate issues raised in this derivation, like the neglect of quantum correlations between spins on different molecules at (repeated) initial times, are discussed with the help of exact calculations (for all spin temperatures) performed on a simplified model which includes equal couplings between all N spins of a system. The same model is used to compare the merits of different forms of ‘‘high temperature’’ approximation. We also propose an iterative scheme for solving the ‘‘modified Bloch–Redfield equations,’’ in which the starting point is the well understood solution of the problem without dipolar field. Finally, a short discussion is given of the relation between ‘‘quantum correlations’’ and ‘‘quantum coherences’’ in the perspective of multiple-pulse and multiple-quantum experiments. These two notions are very simply related in the strict first approximation of weak order, and have often not been clearly distinguished. However, in the second order approximation, which is required whenever dipolar field effects manifest themselves, unrelated spins may display observable coherences although they are not coupled (hence not correlated).