Time-dependent Coupling Parameter Research Articles

Quantum Control of a Nonlinear Time-Dependent Interaction of a Damped Three-Level Atom

We investigate some new aspects of the nonlinear interaction between a three-level Ξ-type atom and bimodal field. The photon-assisted atomic phase damping, detuning parameter, Kerr nonlinearity and the time-dependent coupling have been considered. The general solution has been obtained by using the Schrődinger equation when the atom and the field are initially prepared in the excited state and coherent state, respectively. The atomic population inversion and concurrence are discussed. It is shown that the time-dependent coupling parameter and the detuning parameter can be considered as quantum controller parameters of the atomic population inversion and quantum entanglement in the considered model.

Characteristics of the temporal behavior of quantum Fisher information and entanglement between radiation field and two atoms under atomic motion effect

The influence of time dependence on the model which consists of two qubits interacting with a two-mode electromagnetic field of the parametric amplifier type is investigated. The analytical solution of the wave function is obtained. The quantum Fisher information, entanglement and population inversion for a time-dependent system are analyzed. The photon statistics of a single-mode are quantified by the evolution of the Mandel parameter. Our results showed that there exists a positive relationship between the time-dependent parameter and entanglement. In other words, the time-dependent parameter due to the degree of entanglement is increased. Also, the quantum quantifier is strongly affected by the time-dependent coupling parameter in the absence and presence of the detuning parameter. This enables new parameters to control the degree of entanglement and quantum Fisher information, especially in quantum communication.

On the Interaction Between a Time-Dependent Field and a Two-Level Atom: Path Integral Treatment

We use the coherent state path integral and a Schwinger model for the spin to solve the generalized Jaynes-Cummings model with a time-dependent coupling parameter of the photons-field. The propagators are given explicitly as perturbation series. These are summed up exactly. The wave functions are deduced.

Combined Molecular Dynamics Simulation and Rouse Model Analysis of Static and Dynamic Properties of Unentangled Polymer Melts with Different Chain Architectures

Chain architecture effect on static and dynamic properties of unentangled polymers is explored by molecular dynamics simulation and Rouse mode analysis based on graph theory. For open chains, although they generally obey ideal scaling in chain dimensions, local structure exhibits nonideal behavior due to the incomplete excluded volume (EV) screening, the reduced mean square internal distance (MSID) can be well described by Wittmer’ theory for linear chains and the resulting chain swelling is architecture dependent, i.e., the more branches a bit stronger swelling. For rings, unlike open chains they are compact in term of global sizes. Due to EV effect and nonconcatenated constraints their local structure exhibits a quite different non-Gaussian behavior from open chains, i.e., reduced MSID curves do not collapse to a single master curve and fail to converge to a chain-length-independent constant, which makes the direct application of Wittmer’s theory to rings quite questionable. Deviation from ideality is further evidenced by limited applicability of Rouse prediction to mode amplitude and relaxation time at high modes as well as the non-constant and mode-dependent scaled Rouse mode amplitudes, while the latter is architecture-dependent and even molecular weight dependent for rings. The chain relaxation time is architecture-dependent, but the same scaling dependence on chain dimensions does hold for all studied architectures. Despite mode orthogonality at static state, the role of cross-correlation in orientation relaxation increases with time and the time-dependent coupling parameter rises faster for rings than open chains even at short time scales it is lower for rings.

Dynamical dark sectors and neutrino masses and abundances

We investigate generalized interacting dark matter-dark energy scenarios with a time-dependent coupling parameter, allowing also for freedom in the neutrino sector. The models are tested in the phantom and quintessence regimes, characterized by an equation of state $w_x<-1$ and $w_x>-1$, respectively. Our analyses show that for some of the scenarios the existing tensions on the Hubble constant $H_0$ and on the clustering parameter $S_8$ can be significantly alleviated. The relief is either due to \textit{(a)} a dark energy component which lies within the phantom region; or \textit{(b)} the presence of a dynamical coupling in quintessence scenarios. The inclusion of massive neutrinos into the interaction schemes does not affect neither the constraints on the cosmological parameters nor the bounds on the total number or relativistic degrees of freedom $N_{\rm eff}$, which are found to be extremely robust and, in general, strongly consistent with the canonical prediction $N_{\rm eff}=3.045$. The most stringent bound on the total neutrino mass $M_{\nu}$ is $M_{\nu}<0.116$ eV and it is obtained within a quintessence scenario in which the matter mass-energy density is only mildly affected by the presence of a dynamical dark sector coupling.

New features of non-linear time-dependent two-level atoms

Abstract In this paper, two-level atoms interacting with a single-mode radiation field alongside important properties are presented. The model presented discusses multi-photon process and it has also a nonlinear Kerr-medium and Stark-shift. In addition, the coupling parameter is discussed in a time-dependent fashion. The results show that Stark-shift, time-dependent coupling parameter, and nonlinear Kerr-medium play significant roles regarding the evolution of the von-Neumann entropy and the system's geometric phases. We've used accessible parameters to examine these observations, and some new results are obtained. Remarkably, the geometric phase shows high sensitivity to any change of the considered parameters.

A moving three-level Λ-type atom in a dissipative cavity

In this paper, we consider a three-level Λ-type atom interacting with a two-mode of electromagnetic cavity field surrounded by a nonlinear Kerr-like medium, the atom and the field are suffering decay rates (i.e. the cavity is not ideal) when the multi-photon processes is considered. Also, the atom and the field are assumed to be coupled with a modulated time-dependent coupling parameter under the rotating wave approximation. The wave function and the probability amplitudes are obtained, when the atom initially prepared in the superposition states and the field initially in the coherent states, by solving the time-dependent Schrodinger equation by taking a proper approximation to the system of differential equations. An analytical expression of the atomic reduced density operator is given. We studied the degree of entanglement, between the field and atom, measure (DEM) via the concurrence, Shannon information entropy, momentum increment and diffusion, and finally we investigated the effects of decay rates and the time-dependent parameters on Husimi Q-function.

Entanglement Dynamics of a Three-level Atom in a Momentum Eigenstate Interacting with Non-linear Effect

We consider a general Hamiltonian for a system which consists of a three level lambda configuration atom interacting with a one-mode cavity field. Besides the intensity-dependent coupling the model includes multi-photon process as well as a non-linear Kerr-Like medium effect. Furthermore, the atom and the field are assumed to be coupled with modulated coupling parameter which depends explicitly on time. The atom is initially prepared in a superposition state and field in a coherent state. Under a rotating wave approximation where fast oscillations are ignored, an exact solution for the wave function in Schrodinger equation is obtained. The momentum increment, the momentum diffusion and the field entropy are calculated. The results shown that in existence of the time dependent coupling parameter leads to a time delaying in the interaction which is twice the delay time for the independent case. The general conclusions reached are illustrated by numerical results.

Coupling functions in networks of oscillators

Networks of interacting oscillators abound in nature, and one of the prevailing challenges in science is how to characterize and reconstruct them from measured data. We present a method of reconstruction based on dynamical Bayesian inference that is capable of detecting the effective phase connectivity within networks of time-evolving coupled phase oscillators subject to noise. It not only reconstructs pairwise, but also encompasses couplings of higher degree, including triplets and quadruplets of interacting oscillators. Thus inference of a multivariate network enables one to reconstruct the coupling functions that specify possible causal interactions, together with the functional mechanisms that underlie them. The characteristic features of the method are illustrated by the analysis of a numerically generated example: a network of noisy phase oscillators with time-dependent coupling parameters. To demonstrate its potential, the method is also applied to neuronal coupling functions from single- and multi-channel electroencephalograph recordings. The cross-frequency δ, α to α coupling function, and the θ, α, γ to γ triplet are computed, and their coupling strengths, forms of coupling function, and predominant coupling components, are analysed. The results demonstrate the applicability of the method to multivariate networks of oscillators, quite generally.

Two coupled oscillators in the form of a frequency converter in interaction with a single atom via two-photon processes

We consider the problem of a two-level atom with degenerate two-photon transitions interacting with a single-mode radiation field in the presence of a parametric frequency-converter term. A Hamiltonian representing such a system contains three time-dependent coupling parameters. We obtain an exact solution of the wave function in the Schrodinger picture, using the canonical transform and under a certain choice of the coupling parameters. We use the results obtained to discuss the atomic inversion as well as the linear entropy in addition to both the variance and entropy squeezing. We show that the system at a certain time is sensitive to variations in both the detuning parameter Δ and the ratio of the coupling parameter g.

Time-Dependent Orientation Coupling in Equilibrium Polymer Melts

The motion in concentrated polymer systems is described by either the Rouse or the reptation model, which both assume that the relaxation of each polymer chain is independent of the surrounding chains. This, however, is in contradiction with several experiments. In this Letter, we propose a universal description of orientation coupling in polymer melts in terms of the time-dependent coupling parameter κ(t). We use molecular dynamics simulations to show that the coupling parameter increases with time, reaching about 50% at long times, independently of the chain length or blend composition. This leads to predictions of component dynamics in mixtures of different molecular weights from the knowledge of monodisperse dynamics for unentangled melts. Finally, we demonstrate that entanglements do not play a significant role in the observed coupling.

Creation of entanglement and implementation of quantum logic gate operations using a three-dimensional photonic crystal single-mode cavity

We solve the Jaynes-Cummings Hamiltonian with time-dependent coupling parameters under dipole and rotating-wave approximation for a three-dimensional (3D) photonic crystal (PC) single mode cavity with a sufficiently high quality (Q) factor. We then exploit the results to show how to create a maximally entangled state of two atoms, and how to implement several quantum logic gates: a dual-rail Hadamard gate, a dual-rail NOT gate, and a SWAP gate. The atoms in all of these operations are syncronized, which is not the case in previous studies [1,2] in PCs. Our method has the potential for extension to N-atom entanglement, universal quantum logic operations, and the implementation of other useful, cavity QED based quantum information processing tasks.

Entropy squeezing of time dependent single-mode Jaynes–Cummings model in presence of non-linear effect

A general Hamiltonian for a system which consists of a two-level atom interacting with electromagnetic field is considered. Besides the Stark shift the model includes multi-photon process as well as a non-linear Kerr-like medium effect. Furthermore the field and the atom are assumed to be coupled with modulated coupling parameter which depends explicitly on time. Under an approximation where fast oscillations are ignored, an exact solution for the wave function in Schrödinger picture is given. The atomic inversion as well as the entropy squeezing are considered and it has been shown that existence of the time dependent coupling parameter leads to a time delaying in the interaction which is twice the delay time for the independent case.

Quantum treatment of the time-dependent coupled oscillators

The Hamiltonian for a system of two coupled oscillators with time-dependent coupling parameter and the phase pump is considered. The wavefunction in Schrödinger picture and the Green function are calculated. The squeezing phenomena as well as the Glauber second-order correlation function is discussed. Statistical investigation for the quasi-probability distribution function (P-representation, W-Wigner and Q-functions) are given.