The European Physical Journal D最新文献

In quantum phase estimation, the Heisenberg limit provides the ultimate accuracy over quasi-classical estimation procedures. However, realizing this limit hinges upon both the detection strategy employed for output measurements and the characteristics of the input states. This study delves into quantum phase estimation using s-spin coherent states superposition. Initially, we delve into the explicit formulation of spin coherent states for a spin (s=3/2). Both the quantum Fisher information and the quantum Cramer–Rao bound are meticulously examined. We analytically show that the ultimate measurement precision of spin cat states approaches the Heisenberg limit, where uncertainty decreases inversely with the total particle number. Moreover, we investigate the phase sensitivity introduced through operators (e^{izeta {S}_{z}}), (e^{izeta {S}_{x}}) and (e^{izeta {S}_{y}}), subsequently comparing the resultants findings. In closing, we provide a general analytical expression for the quantum Cramér–Rao bound applied to these three parameter-generating operators, utilizing general s-spin coherent states. We remarked that attaining Heisenberg-limit precision requires the careful adjustment of insightful information about the geometry of s-spin cat states on the Bloch sphere. Additionally, as the number of s-spin increases, the Heisenberg limit decreases, and this reduction is inversely proportional to the s-spin number.

The effects of absorption and saturation on soliton states in Kerr-type nonlinear layers are theoretically investigated. In addition to the usual gray and bright soliton structures observed in nonlinear slabs, a flat soliton, i.e., a particular soliton excitation with electric field amplitude independent of the position within the layer, is researched in cases of self-defocusing and self-focusing nonlinearities. Effects caused by the combination of absorption and saturation, such as the shift and extinction of the flat soliton peak, the decrease in the amplitude of the electric field within the nonlinear layer, and the suppression of the multistable behavior of the transmission coefficient in the vicinity of the soliton peaks, are discussed. The present theoretical results are compared and found in good quantitative agreement with previous experimental measurements.

We present a progress report on the development of PyXstar, a Python package to manage the data (input, output, intermediate, atomic database, and model-grids) associated with the xstar code for treating photoionized and collisionally ionized plasmas. The PyXstar modular structure and database retrieval scheme are described, and its functionality is illustrated with Python functions and classes for performing database searches. We briefly compare PyXstar with two other Python spectrum modeling tools: PyNeb and PyAtomDB.

The existing notion of the shared entangled state-assisted remote preparation of unitary operator (equivalently the existing notion of quantum remote control) using local operation and classical communication is generalized to a scenario where under the control of a supervisor two users can jointly implement arbitrary unitaries (one unknown unitary operation by each or equivalently a single unitary decomposed into two unitaries of the same dimension and given to two users) on an unknown quantum state available with a geographically separated user. It is explicitly shown that the task can be performed using a four-qubit hyperentangled state, which is entangled simultaneously in both spatial and polarization degrees of freedom of photons. The proposed protocol which can be viewed as primitive for distributed photonic quantum computing is further generalized to the case that drops the restrictions on the number of controllers and the number of parties performing unitaries and allows both the numbers to be arbitrary. It is also shown that all the existing variants of quantum remote control schemes can be obtained as special cases of the present scheme.

Superradiant phase transition and entanglement entropy in the Dicke model with a squeezed light are investigated. We find a special rotation coordinate system mapping the original Hamiltonian into an effective dual-oscillator Hamiltonian in the thermodynamic limit. We analytically derive the eigenenergy and eigenstate of the ground state. The ground state is demonstrated to undergo superradiant phase transition at a nonlinear critical boundary collectively induced by the squeezed driving and qubit-field coupling. This phase boundary requires neither large qubit-field detuning nor strong squeezed driving. An exact expression of the ground-state entropy is obtained. We demonstrate that the squeezed light enhances the qubit-field entanglement entropy linearly.

A theoretical inquiry delves into the presence of multiple solitons and breather configurations within a nonuniform, inhomogeneous, unmagnetized dusty plasma characterized by universally polarized force. This system encompasses ions, electrons, positively and negatively charged dust particles, distributed in accordance with a superthermal distribution. Employing the reductive perturbation technique (RPT), the Gardner equation (GE) is derived from the fundamental hydrodynamical model equations. The multi-solitons of the GE are synthesized utilizing the Hirota bilinear method (HBM), which further facilitates the exploration of breather solutions via the appropriate selection of complex wave numbers. The system exhibits both compressive and rarefactive multi-solitons. Moreover, the behavior of breather structures varies depending on associated plasma parameters; occasionally, they overlap, while at other times, they remain entirely disjoint. This research holds relevance for investigating the propagation of finite-amplitude waves in natural phenomena such as the atmosphere, oceans, optic fibers, and signal processing.

Figures display the interaction between two-solitons (a), and breather structures (b), of the Gardner equation in dusty plasma with polarized force for the parameter values (k_i = 5, k_e = 2.5, mu _i = 0.7, mu _e = 0.3, mu = 10, rho = 1.01, sigma _i = 0.1, R = 0.5, Z = 0.01), respectively. The manuscript presents some graphs to illustrate the propagation and interaction between two-soliton solutions, as well as the propagation of various breather structures in dusty plasma under polarized force. We explore the presented wave solutions using the symbolic computation software Mathematica. The diversity in two-solitons and breather structures depends on the plasma parameter and the choice of wave number, real or complex. This work analyzes, through graphical representation, how the plasma system affects the above nonlinear structures.

In this theoretical investigation, we have performed comprehensive quantum calculations to explore the pressure broadening effects on the (D_{1}left( 3,stext { }^{2}S_{1/2}-3ptext { }^{2}P_{1/2}right) ) and (D_{2}left( 3,s text { }^{2}S_{1/2}-3ptext { }^{2}P_{3/2}right) ) lines of the Mg( ^{+}) magnesium ion when surrounded by ground-state He helium atoms. Our objective is to delineate the profiles of these pressure-broadened resonance lines and scrutinize their behavior in response to binary collisions between Mg(^{+}) ions and He atoms. To accomplish this goal, we developed precise potential energy curves for the ground (X ^{2}Sigma _{1/2}^{+}) and the excited (A^{2}Pi _{1/2},A^{2}Pi _{3/2}) and B (^{2}Sigma _{1/2}^{+}), along with the associated transition dipole moments, using data derived from advanced ab initio methodologies such as SA-CASSCF, MRCI, and SO coupling, with Davidson and BSSE corrections. Our investigation encompasses a temperature range from 4000 to (12000 ,textrm{K}) and wavelengths spanning from 200 to (450,textrm{nm}). The theoretical profiles primarily exhibit dominant free-free transitions. Notably, around the (235,textrm{nm}) wavelength region, a satellite peak appears in the blue wing, attributed to the B (^{2}Sigma _{1/2}^{+}longleftarrow X ^{2}Sigma _{1/2}^{+}) transitions. We have confirmed agreement between our theoretical findings and prior research.

A Fabry–Perot interferometry was used to measure with a precision of about (10^{-4}) the Landé factor values of the levels issued from the 5s5p, 5s6d, 5s6s and 5s7p configurations of cadmium. Fully relativistic MCDHF calculations taking into account Breit and QED effects were performed to interpret the results of the experiment performed on the cadmium isotope 114. In addition to the four experimental Landé (g_J) values, new theoretical results for 12 levels are reported for the first time.