Dynamics of electromagnetic field in two-level doped systems

The dynamics of solitons of self-inducted transparency is theoretically and numerically investigated in the case when atoms described in the two-level approximation fit into a medium with ferroelectric properties. The interaction between electromagnetic pulses in the medium and two-level dopant atoms is considered.     

Protecting quantum coherence of two-level atoms from vacuum fluctuations of electromagnetic field

In the framework of open quantum systems, we study the dynamics of a static polarizable two-level atom interacting with a bath of fluctuating vacuum electromagnetic field and explore under which conditions the coherence of the open quantum system is unaffected by the environment. For both a single-qubit and two-qubit systems, we find that the quantum coherence cannot be protected from noise when the atom interacts with a non-boundary electromagnetic field. However, with the presence of a boundary, the dynamical conditions for the insusceptible of quantum coherence are fulfilled only when the atom is close to the boundary and is transversely polarizable. Otherwise, the quantum coherence can only be protected in some degree in other polarizable direction.     

Ultrashort pulses of an electromagnetic field in a planar waveguide array with two-level systems

A planar homogeneous waveguide array with two-level systems has been considered. The evolution of an electromagnetic field is described by the Maxwell-Bloch equations taking into account the action of the fields of neighboring waveguides beyond the slow-envelope approximation. It has been shown that the model in the continuous approximation is reduced to an integrable system of equations, including the case of a nonzero static dipole moment. The model can be used to analyze the nonlinear mechanism of the compression of pulses and the conditions of overcoming of the diffraction limit.     

Ultrashort pulses of an electromagnetic field in a planar waveguide array with two-level systems

JETP Letters - A planar homogeneous waveguide array with two-level systems has been considered. The evolution of an electromagnetic field is described by the Maxwell-Bloch equations taking into...     

Theory of absorption of electromagnetic radiation by highly inhomogeneous two-component systems

Calculations are made of the permittivity of a composite formed by a mixture of a dielectric matrix and macroscopic magnetic inclusions. It is shown that the dielectric loss tangent in this material is a complex function of their concentration x, and this function is determined. The dependence of the absorption maximum on x is determined and it is shown that the maximum is only observed in the presence of foreign inclusions. Conditions for the existence of an absorption maximum are obtained for the two most interesting physical cases. A method of calculating the components of the depolarization tensor is proposed for a thin-film composite. Zh. Tekh. Fiz. 69, 89–94 (July 1999)     

Nonlinear interaction between a two-level atom and a weak polychromatic field

The interaction between two-level media and a polychromatic field is considered in the limit of small field amplitudes. The obtained third-order corrections allow us to describe a nonlinear response to the field and intermodal interaction. The obtained polarization spectra are compared to numerical solutions to the density matrix equation in the rotating wave approximation. The results can be used in nonlinear comb spectroscopy.     

Time optimal control of two-level quantum systems

The objective of time-optimal control that helps to minimize relaxation losses, is the evolution of a quantum state from a given initial mixed state to a final target mixed state in minimum time. In this paper, we study a time-optimal control problem of the dynamic of a pure two-level system with unbounded control using Pontryagin's minimum principle and obtain the minimal time for some initial and final states. The results will apply to basically all qubit systems that one can consider such as NMR spectroscopy, trapped ions, superconducting qubits, etc. We also show that these results hold for pure states, and only the direction $\hat{n}$ is important in the evolution of a quantum state. In this work, the problem of computing minimum time to produce any unitary transformation $U_f\in SU(2)$ is reduced to finding the minimum time to steer the system from an initial to a final state.     

Features of absorption of a weak electromagnetic wave in nanowires

Interband and intersubband optical transitions in quantum wires are studied theoretically with allowance for scattering of carriers both by long-wavelength acoustic fluctuations and by a rough surface. The frequency dependence of the coefficient of light absorption is shown to be described by a bell-shaped curve, the half-width of which depends on the temperature and radius of the nanowire. The theoretical results are compared with experimental data on optical properties of Bi nanowires. In particular, it is shown that scattering of carriers by a rough surface at low temperatures must be taken into account for a satisfactory agreement between the theory and experiment.     

太赫兹电磁场照射下量子线中的纳米电子力

研究两端连接电子库的量子线在太赫兹(THz)电磁场横向辐射下的电子力学问题. 在自由电子近似下求得了弹道区二能级电子波函数解析表达式,发现电子概率在两个能态间随线轴坐标作Rabi振荡, 其幅度与外场强度和频率有关. 利用热力学统计算符方法并利用波函数计算出了传导电子对量子线中张力贡献的大小. 其计算结果可表示成与外场无关和与外场有关的两部分之和,前者与已有的实验观测和理论计算结果一致, 而与外场参量有关的部分可用量子相干理论解释. 关键词： 量子线 THz电磁场 纳米电子力     

Exciton states and excitonic absorption spectra in a cylindrical quantum wire under transverse electric field

The temperature dependence of the resistance in trilayer graphene is observed under different applied gate voltages. At small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs, characteristic of a semimetal. At large gate voltages excitation of electron-hole pairs is suppressed, and the resistance increases with increasing temperature because of the enhanced electron-phonon scattering, characteristic of a metal. We find that the simple model with overlapping conduction and valence bands, each with quadratic dispersion relations, is unsatisfactory. Instead, we conclude that impurities in the substrate that create local puddles of higher electron or hole densities are responsible for the residual conductivity at low temperatures. The best fit is obtained using a continuous distribution of puddles. From the fit the average of the electron and hole effective masses can be determined.     

Linear feedforward control of two-level quantum system by modulated external field

We propose a model of feedforward (open-loop) optical control of two-level atom in the linear form. This model allows to express the general form of solution for the atomic level populations via the arbitrary shapes of the control signal. Then we make numerical investigations of different shapes for the optical control signal.     

Polynomial pseudosupersymmetry underlying a two-level atom in an external electromagnetic field

We study chains of transformations introduced in B.F. Samsonov and V.V. Shamshutdinova: J. Phys. A: Math. Gen. 38 (2005) 4715, in order to obtain electric fields with a time-dependent frequency for which the equation of motion of a two-level atom in the presence of these fields can be solved exactly. We show that a polynomial pseudosupersymmetry may be associated to such chains. Presented at the 3rd International Workshop “Pseudo-Hermitian Hamiltonians in Quantum Physics”, Istanbul, Turkey, June 20–22, 2005.     

Exciton binding energy and excitonic absorption spectra in a parabolic quantum wire under transverse electric field

The effects of transverse electric field on the energy levels of electron and heavy hole, exciton binding energy and excitonic absorption spectra of GaAs parabolic quantum wire are theoretically investigated in detail. The results indicate that the electron and hole energy levels, exciton binding energy, excitonic absorption coefficient and absorption energy becomes smaller with the increase of electric field. That is more significant at the condition of weaker parabolic confinement potential. The phenomena can be explained by the separation of overlap integral of the electron and hole at the ground states.     

Intersubband optical absorption in two-level quantum wells embedded in a planar microcavity

A theoretical analysis of the optical absorption including both the linear and third-order non-linearity arising from intersubband transitions in two-level quantum wells, which are embedded in a planar microcavity, has been performed. Starting from the Maxwell–Lorentz equations, the expressions of the field in each layer are explicitly given, and the field in the quantum wells is determined via an integral equation, in which the third-order non-linearity is included. Then, by matching the boundary conditions, the field in the quantum-well microcavity structure is rigorously determined, and the absorption coefficient is thus obtained. Detailed numerical calculations show that the optical intersubband absorption can be significantly modified due to the coupling between the quantum wells and the microcavity. This revised version was published online in November 2006 with corrections to the Cover Date.     

Frequency shifts in emission and absorption by resonant systems ot two-level atoms

The frequency shifts in emission and absorption arising from resonant many-body interactions in a system of two-level atoms are discussed from several points of view: (1) in the language of superradiance, Dicke states, quantum electrodynamics and perturbation theory; (2) in the classical-path treatment of gaseous emission, with emphasis on the impact approximation; (3) by means of diagrams related to the temperature-Green's function formalism; (4) in the semiclassical model using the macroscopic Bloch vector; (5) through ordinary classical electromagnetic theory in a linear medium.     

周期多层量子阱结构的光吸收特性与电场分布

研究周期多层量子阱(MQW)结构的线性光学吸收特性与共振入射脉冲能量宽度、结构层数以 及周期的关系.结果表明:窄共振脉冲激发下的Bragg结构在层数达到某一值后,总吸收由随层 数单调增加变为单调减少;在非Bragg排列条件下则一直单调增加.通过对结构内电磁场强度 分布情况的分析解释了以上结果的来源,并指出吸收的Bragg压缩效应的实验条件. 关键词： 多量子阱 周期结构 吸收特性