Sideband manipulation of population inversion in a three-level Λ atomic system

Sideband manipulation of population inversion in a three-level A atomic configuration is investigated theoretically. Compared with the case of a nearly monochromatic field, a population inversion between an excited state and a ground state has been found in a wide sideband intensity range by increasing the difference in frequency between three components. Furthermore, the population inversion can be controlled by the sum of the relative phases of the sideband components of the trichromatic pump field with respective to the phase of the central component. Changing the sum phase from 0 to π, the population inversion between the excited state and the ground state can increase within nearly half of the sideband intensity range. At the same time, the sideband intensity range that corresponds to the system exhibiting inversion ρ00 〉 ρ11 also becomes wider evidently.     

Electromagnetically induced transparency and electromagnetically induced absorption in Y-type system

The propagation of a probe field through a four-level Y-type atomic system is described in the presence of two additional coherent radiation fields, namely, the control field and the coupling field. An expression for the probe response is derived analytically from the optical Bloch equations under steady state condition to study the absorptive properties of the system under probe field propagation through an ensemble of stationary atoms as well as in a Doppler broadened atomic vapor medium. The most striking result is the conversion of electromagnetically induced transparency(EIT) into electromagnetically induced absorption(EIA) as we start switching from weak probe regime to strong probe regime. The dependence of this conversion on residual Doppler averaging due to wavelength mismatch is also shown by choosing the coupling transition as a Rydberg transition.     

Resonant rayleigh scattering from bilayer quantum Hall phases

We observe resonant Rayleigh scattering of light from quantum Hall bilayers at Landau level filling factor nu = 1. The effect arises below 1 Kelvin when electrons are in the incompressible quantum Hall phase with strong interlayer correlations. Marked changes in the Rayleigh scattering signal in response to application of an in-plane magnetic field indicate that the unexpected temperature dependence is linked to formation of a nonuniform electron fluid close to the phase transition towards the compressible state. These results demonstrate a new realm of study in which resonant Rayleigh scattering methods probe quantum phases of electrons in semiconductor heterostructures.     

Phase Dependence of Fluorescence Spectrum of a Two-Level Atom in a Trichromatic Field

We examine the phase-dependent effects in resonance fluorescence of a two-level atom driven by a trichromatic modulated field. It is shown that the fluorescence spectrum depends crucially on the sum of relative phases of the sideband components compared to the central component, not simply on the respective phases. The appearance or disappearance of the central peak and the selective elimination of the sideband peaks are achieved simply by varying the sum phase. Once the sum phase is fixed, the spectrum keeps its features unchanged regardless of the respective relative phases.     

Absorption interferometer of two-sided cavity

We propose a scheme in which an arbitrary incidence can be made perfectly reflected/transmitted with a phase modulator. We analyze the variation of intracavity field as well as output field with closed-loop phase φ1 of the control fields and relative phase φ2 of the probe beams. With two phases, medium absorption and light interference can be controlled so that photon escape from the cavity can be manipulated, thus an intensity switching based on phase modulation can be realized. And the condition for perfect transmitter or reflector is obtained. Then based on the transmission/reflection analysis,the total absorption of this system can be investigated. Therefore our scheme can be used as an absorption interferometer to explore the optical absorption in some complicated system. The state delay of the output light intensity, which is dependent on φ1 or φ2, can be applied in the realization of quantum phase gate and subtle wave filter. And based on this scheme, we implement the state transfer between perfect transmitter/reflector and non-perfect coherent photon absorber via relative-phase modulation.     

Optical probe,local fields,and Lorentz factor in ferroelectrics

An optical probe is suggested that allows measurements of the local field and Lorentz factor (L) in ferroelectric medium. The copolymer poly (vinylidene fluoride/trifluoroethylene) is mixed with Pd-tetraphenylporphyrin (TPP-Pd) that has a very narrow absorption band. Thus, TPP-Pd serves as a molecular optical probe of the local field. During the switching of the electric field lower than the coercive one the factor L of an unpolarized ferroelectric mixture is found to be of about 1/3 that corresponds to the random distribution of molecular dipoles in the ferroelectric. With increasing field, the dipole orientation acquires a lower symmetry and L tends to zero as predicted by lattice sum calculations for vinylidene fluoride. The knowledge of the field dependence of L and the usage of the optical probe makes it possible to measure directly the local and macroscopic fields in the individual elements of various ferroelectric-dielectric heterostructures.     

Phase-controlled absorption-gain properties and optical switching in nanodiamond nitrogen-vacancy center

We study phase-controlled absorption-gain and dynamic switching behaviors in a nanodiamond nitrogen-vacancy (NV) center. The NV center is driven coherently by a weak probe laser field, a control laser field and a microwave field. To describe the transient behavior of the system, we go beyond the steady-state approximation and simultaneously solve the coupled Bloch–Maxwell equations for the NV center and the probe field on numerical grids as functions of space and time. The results show that the continuous-wave input weak probe field can be switched on and off when the relative phase of the applied field is externally varied periodically in time. The proposed scheme may have applications in the design of optical switching and optical gain devices.     

Controlling the optical bistability beyond the multi-photon resonance condition in a three-level closed-loop atomic system

We investigate the optical bistability behavior of a three-level closed-loop atomic system beyond the multi-photon resonance condition. Using the Floquet decomposition, we solve the time-dependent equations of motion, beyond the multi-photon resonance condition. By identifying the different scattering processes contributing to the medium response, it is shown that in general the optical bistability behavior of the system is not phase-dependent. The phase dependence is due to the scattering of the driving and coupling fields into the probe field at a frequency, which, in general, differs from the probe field frequency.     

Bichromatic and trichromatic manipulation of spontaneous emission in a three-level Λ system

Bichromatic and trichromatic manipulation of spontaneous emission in a three-level system in Λ configuration is studied on the basis of density matrix equation and quantum regression theorem. The spontaneous emission spectrum is numerically calculated by using harmonic expansion and matrix inversion. Two characteristic features are shown. Firstly, the central resonance peak, which is absent in the case of monochromatic excitation, is recovered for the bichromatic or trichromatic excitation. Secondly, selective elimination of the spectral lines is obtained by varying the amplitudes and phases of the trichromatic components. For the phase dependence, it is the sum of the relative phases of the two sideband components to the central component that plays a crucial role. The spontaneous emission spectrum is drastically modified once the sum phase is changed, but is kept unchanged regardless of the respective phases when the sum phase is fixed.     

Transient electromagnetically induced transparency spectroscopy of 87Rb atoms in buffer gas

We study the transient response dynamics of ⁸⁷Rb atomic vapor buffered in 8 torr Ne gas through an electromagnetically induced transparency configured in $\varLambda$-scheme. Experimentally, the temporal transmission spectra versus probe detuning by switching on and off the coupling one show complex structures. The transmitted probe light intensity drops to a minimum value when the coupling light turns off, showing a strong absorption. Even at the moment of turning on the coupling light at a subsequent delayed time, the atomic medium shows a fast transient response. To account for the transient switching feature, in the time-dependent optical Bloch equation, we must take the transverse relaxation dephasing process of atomic vapor into account, as well as the fluorescence relaxation along with the optical absorption. This work supplies a technique to quantify the transverse relaxation time scale and to sensitively monitor its variation along the environment by observing the transient dynamics of coherent medium, which is helpful in characterizing the coherent feature of the atomic medium.     

Dispersive and absorptive properties of a <Emphasis Type="Italic">Λ</Emphasis>-type atomic system with two fold lower-levels

The dispersion and the absorption properties of a driven four-level Λ-type atomic system is investigated. It is found that the interaction of double-dark states lead to controllable group velocity of the weak probe field by the intensity of driving field and the relative phase between applied fields. Moreover, the transient dispersion, absorption and the group index are also discussed. The required switching time for switching the group velocity of a weak probe field from subluminal to superluminal pulse propagation is then discussed.     

Phase switching and quantum interference in a 3-level Λ-shape bistable model

The steady state bistable behaviour of a three-level Λ-shape is examined in the presence of a control field $({\rm \Omega} +\chi \left( t\right) e^{i\varphi})$({\rm \Omega} +\chi \left( t\right) e^{i\varphi}) : Ω is the strong Rabi component, $\chi \left( t\right) $\chi \left( t\right) is the stochastic part with relative phase ϕ; with quantum interference between decay channels taken into account. One- and two-way phase switching effect for the transmitted field against the phase are predicted at fixed values for the incident input field. Also cooperative switching effect shows multistable/bistable behaviour. Quantum interference tends to diminish the dispersive effects responsible for multistable behaviour (in the input-output relation and the cooperative switching diagram) and asymmetry (in the phase switching diagram). Equivalence of the role of the stochastic part of the control field with that of the “classically” squeezed field is shown to occur only in the absence of quantum interference.     

Phase-shift extraction from twice-normalized light intensity changes recorded with random phase shifts

A simple phase-shift extraction algorithm is proposed for interferograms recorded with random phase shifts that vary over at least 2π. The phase-shift-dependent changes in the intensity at two pixels having different phases, selected from one frame, are taken out and normalized. The sum and difference of the two normalized changes are calculated, and both the changes are normalized again along the phase shifts. The normalized sum and difference become the cosine and sine of a term including the random phase shift, respectively. Thereby, the phase shifts are extracted from both twice-normalized intensity changes. An experiment using an interference microscope equipped with a piezoelectric-transducer positioner of an objective lens is conducted to estimate the validity of the algorithm. The algorithm is verified to have satisfactory results when the multiple interferograms used have a sample size of more than 15 frames recorded with random phase shifts.     

Ultrashort pulse generation in the medium with induced optical anisotropy

Abilities of the method of accumulation of coherent unstable response of a medium for amplification of the rotated component of the probe wave’s polarization in the atomic medium of three-level atoms are studied. Probe wave is examined in frames of the perturbation theory and its frequency is considered near to one photon resonance from the ground to the first excited level. The intense monochromatic pump field connects two excited energy levels and propagates through the medium without a change. The broadening of spectral lines caused by the relaxation processes and the Doppler broadening are included into the calculations. It is shown that by multiple consistent instantaneous change of input probe field’s phase from 0 to π and back, it is possible to obtain, in the tail part of the rotated component of the probe field, a separate narrowed light pulse along with the increase in intensity by more than an order of magnitude with respect to the input field.     

Stochastic resonance and nonequilibrium dynamic phase transition of Ising spin system driven by a joint external field

The dynamic response and stochastic resonance of a kinetic Ising spin system （ISS） subject to the joint action of an external field of weak sinusoidal modulation and stochastic white-nolse are studied by solving the mean-field equation of motion based on Glauber dynamics. The periodically driven stochastic ISS shows that the characteristic stochastic resonance as well as nonequilibrium dynamic phase transition （NDPT） occurs when the frequency ω and amplitude h0 of driving field, the temperature t of the system and noise intensity D are all specifically in accordance with each other in quantity. There exist in the system two typical dynamic phases, referred to as dynamic disordered paramagnetic and ordered ferromagnetic phases respectively, corresponding to a zero- and a unit-dynamic order parameter. The NDPT boundary surface of the system which separates the dynamic paramagnetic phase from the dynamic ferromagnetic phase in the 3D parameter space of ho-t-D is also investigated. An interesting dynamical ferromagnetic phase with an intermediate order parameter of 0.66 is revealed for the first time in the ISS subject to the perturbation of a joint determinant and stochastic field. The intermediate order dynamical ferromagnetic phase is dynamically metastable in nature and owns a peculiar characteristic in its stability as well as the response to external driving field as compared with a fully order dynamic ferromagnetic phase.     

Characterization of the cholesteric phase of filamentous bacteriophage fd for molecular alignment

Residual dipolar couplings arise from small degrees of alignment of molecules in a magnetic field and have proven to provide valuable structural information. Colloidal suspensions of rod-shaped viruses and bacteriophages constitute a frequently employed medium for imparting such alignment onto biomolecules. The stability and behavior of the liquid crystalline phases with respect to solution conditions such as pH, ionic strength, and temperature vary, and characterization should benefit practical applications as well as theoretical understanding. In this Communication we describe the pH dependence of the cholesteric liquid crystalline phase of the filamentous bacteriophage fd and demonstrate that the alignment tensor of the solute protein is modulated by pH. We also report the interesting observation that the relative sign of the residual dipolar coupling changes at low pH values. In addition, we demonstrate that the degree of alignment inversely scales with the lengths of the phage particles for phages with identical mass and charge per unit length.     

四能级原子系统中电磁感应吸收的相位控制

在以三个电偶极跃迁构成简并N型四能级系统中,利用密度矩阵方程计算了介质对探测场的吸收,研究了激光场拉比相位对吸收的影响.结果表明:介质对探测场的吸收和放大取决于控制场和信号场的拉比相位,且吸收和放大随控制场、信号场的拉比相位改变而作周期性变化,周期为2π;而探测场的拉比相位变化对吸收没有影响.同时,控制场、信号场拉比相位对吸收的影响是相同的,而且拉比相位主要影响原子相干,对原子布居影响不大.     

${ \mathcal P }{ \mathcal T }$-symmetry berry phases,topology and ${ \mathcal P }{ \mathcal T }$-symmetry breaking

We study the complex Berry phases in non-Hermitian systems with parity- and time-reversal $\left({ \mathcal P }{ \mathcal T }\right)$ symmetry. We investigate a kind of two-level system with ${ \mathcal P }{ \mathcal T }$ symmetry. We find that the real part of the the complex Berry phases have two quantized values and they are equal to either 0 or π, which originates from the topology of the Hermitian eigenstates. We also find that if we change the relative parameters of the Hamiltonian from the unbroken-${ \mathcal P }{ \mathcal T }$-symmetry phase to the broken-${ \mathcal P }{ \mathcal T }$-symmetry phase, the imaginary part of the complex Berry phases are divergent at the exceptional points. We exhibit two concrete examples in this work, one is a two-level toys model, which has nontrivial Berry phases; the other is the generalized Su–Schrieffer–Heeger (SSH) model that has physical loss and gain in every sublattice. Our results explicitly demonstrate the relation between complex Berry phases, topology and ${ \mathcal P }{ \mathcal T }$-symmetry breaking and enrich the field of the non-Hermitian physics.     

Microwave-Controlled Light-Pulse Propagation in a Driven Λ-Type Atomic System with Two-Folded Levels

The temporal and spatial dynamics of one weak probe laser pulse, propagating through a Λ-type atomic medium with two-folded levels under the resonant excitation of one microwave driving field and one strong control field, is investigated in this paper. By numerically solving coupled Bloch-Maxwell equations, it isfound that, in the absence of the microwave driving field, the atomic medium is transparent to the probe pulse at line center, which propagates over sufficiently long distances. By contrast, when the microwave driving field is applied, the probe pulse at line center can be rapidly absorbed on propagation. This substantial reduction of probe transmittance caused by the microwave driving field may lead to potential applications in designing a new kind of optical switching.     

Phase and amplitude control of switching from positive to negative dispersion in superconducting quantum circuits

We study the absorption and dispersion properties of the three-level Δ$\Delta$-type superconducting fluxonium circuit, in which each atomic transition is respectively driven by a coherent classical field. The results show that the absorption and dispersion spectra depend strongly on the relative phase and intensities of the applied fields. When the relative phase is changed from π$\pi$/2 to 3π$\pi$/2, the switching from positive to negative dispersion arises, which can also be obtained via adjusting the relative intensities of the classical fields. Our scheme shows that the dispersion switching effect could be achievable for microwave pulse interacting with the superconducting fluxonium qubit.