Dependence of Electromagnetically Induced Transparency on Laser Linewidth

The influence of the linewidth of coupling laser on the electromagnetically induced transparency (EIT) spectral width is theoretically investigated. The model to describe the EIT spectral width is based on the standard semi-classical theory. The result shows that the effect of the linewidth of coupling laser is equivalent to an additional relaxation between two ground states in the A-type configuration. A broadening linewidth of coupling laser implies the increasing relaxation between the two ground states, which will make the wider EIT spectral linewidth.     

Four-Wave Mixing Scheme in a Four-Level Ladder-Type Atomic System Based on Electromagnetically Induced Transparency

A nonlinear optical four-wave mixing scheme is presented and analysed for the generation of coherent light ina nearly four-level ladder-type atomic system in the context of electromagnetically induced transparency (EIT).We find that EIT can suppress nonlinear photon absorption and the peak of the generated mixing field is locatedat the centre of the transparency window where the loss is minimal, though there is a dip in the centre. Such anonlinear optical process can also be used for generating coherent short-wavelength radiation.     

Generation of High-Dimensional Photon Entangled Coherent States in Double Electromagnetically Induced Transparency System

We present an approach to generate high-dimensional entangled coherent states between photons by using a dense atomic system in a double electromagnetically induced transparency state. The system under our consideration involves an atomic configuration with six internal states, two weak quantized probe lasers, and two strong classical coupling lasers. We show how to generate high dimensional entangled coherent states between the two probe lasers.     

Observation of Electromagnetically Induced Transparency in a Zeeman—Sublevel System in Rubidium Atomic Vapour

We observed electromagnetically induced transparency (EIT) in a Zeeman-sublevel system using rubidium atomic vapour at the temperature of 75~C, in which the width of the EIT signal is only 0.6 MHz. Two different methods were performed to observe the EIT signal in our experiment.     

Direct Measurement of Light Speed Reduction in a Rubidium Vapour Medium Coherently Prepared by Electromagnetically Induced Transparency

We have experimentally observed the reduction of light speed in a rubidium vapour medium coherently preparedby electromagnetically induced transparency. The light speed reduction was deduced by directly measuring thetime delay of a probe light when it passed through the medium. The time delay varies with the intensity of thecoupling laser, and the typical time delay we recorded was 1.8 μs, corresponding to a light speed of 56000 m/s.     

A New Scheme of Entanglement Swapping and Disentanglement

We consider three two-level atoms (A, B, and C) initially in the W entanglement state, then one of them, C, is injected into a high-Q cavity to make resonant interaction to entangle with the other two atoms A and 13 that are far away from the cavity. The entanglement swapping or disentanglement can be realized by carrying out measurements on C and selecting appropriate interaction time of C with the coherent field.     

Observation of Electromagnetically Induced Transparency by a Train of Short Pulses

We report the experimental demonstration of electromagnetically induced transparency in hot rubidium (^85Rb) atomic vapour by using an actively mode-locked external cavity diode laser in Littman-Metcalf configuration. We can make opaque resonant transitions transparent to any two optical comb components in the pulse trains which excite atomic coherence in the ground states of ^85Rb.     

Influence of Multi-Photon Process on Entanglement of Interacting System of the Qubit and Thermal Field

We study the system of a single qubit couples to a single mode thermal field according to a multi-photon Jaynes-Cummings-type interaction with phase decoherence. Both the time evolving entanglement and the stationary state entanglement are calculated by adopting the log-negativity as a measure. It is found that the multi-photonprocess can enhance the stationary state entanglement of this system and can enlarge the range of the parameter Δ/g and the mean photon number of initial thermal field in which the stationary state is distillable.     

Properties of Entropy and Entanglement of Two—Mode Nonlinear Coherent States

In this communication ,two-mode nonlinear coherent states are reviewed and special cases are given,Starting from a three-level atom coupled to two modes of radiation with any form of nonlinearties of the two-mode fields.we derive a Raman-coupled effective Hamiltonian by a unitary transformation,evaluated perturbatively in coupling constants.We use the quantum entropy to measure the degree of entanglement in the time development of an effective two-level atom interacting with two-mode nonlinear-coherent states.The results show that the nolinearity effect yields the superstructure of atomic Radi oscillations and the effect of the Stark shift changes the quasiperiod of the field entropy evolution and entanglement between the particle and the field.A possible experimental test of a new effect is proposed.     

Entanglement Swapping and Disentanglement via an Entangled State of Atoms Interacting with a Cavity Field

We consider entanglement swapping and disentanglement schemes via an entangled state of three two-level atoms interacting with a coherent field.When a two-level atom C,entangled with two other two-level atoms A and B,is injected into a high-Q cavity and atoms A and B are far away from the cavity,the entanglement swapping or disentanglement can be realized by carrying out the measurement on the atom C and by selecting an appropriate interaction time of atom C with the coherent field.     

Generalized Uncertainty Principle and the Quantum Entropy of Rotating Black Hole

The entropy of rotating Kerr-Newman-Kasuya black hole due to massive charged fields （bosons and fermions） is calculated by using the new equation of state density motivated by the generalized uncertainty relation. The result shows the entropy does not depend on the mass and the charge but the parameter A, the area A and the spin of the fields. Moreover, an improved approximation is provided to calculate the scalar entropy.     

Quantum Entanglement in a System of Two Spatially Separated Atoms Coupled to the Thermal Reservoir

We study quantum entanglement between two spatially separated atoms coupled to the thermal reservoir. The influences of the initial state of the system, the atomic frequency difference and the mean number of the thermal field on the entanglement are examined. The results show that the maximum of the entanglement obtained with nonidentical atoms is greater than that obtained with identical atoms. The degree of entanglement is progressively decreased with the increase of the thermal noise. Interestingly, the two atoms can be easily entangled even when the two atoms are initially prepared in the most mixed states.     

多光子Tavis-Cummings模型中两纠缠原子的纠缠演化特性

研究了两个纠缠的二能级原子通过多光子跃迁与单模相干光场进行耦合相互作用系统中两原子纠缠的演化特性.计算分析表明，两个原子之间的纠缠呈现出周期性的演化特性，初始两原子的状态、原子间的偶极相互作用、相干光场的参数以及跃迁光子数对两个原子的纠缠有着显著的影响；并发现两原子初始处于某最大纠缠态时，两原子会永远处于该最大纠缠态，因此这一类最大纠缠态可以作为一种量子信息存储器.     

多光子Tavis-Cummings模型中两纠缠原子的纠缠演化特性

研究了两个纠缠的二能级原子通过多光子跃迁与单模相干光场进行耦合相互作用系统中两原子纠缠的演化特性.计算分析表明,两个原子之间的纠缠呈现出周期性的演化特性,初始两原子的状态、原子间的偶极相互作用、相干光场的参数以及跃迁光子数对两个原子的纠缠有着显著的影响;并发现两原子初始处于某最大纠缠态时,两原子会永远处于该最大纠缠态,因此这一类最大纠缠态可以作为一种量子信息存储器. 关键词： 量子纠缠 部分转置矩阵负本征值 纠缠原子 相干态     

Entanglement and photon statistics of output fields from beam splitter for binomial state inputs

The entanglement properties are investigated based on linear entropy, and nonclassicalities are examined of output fields from a beam splitter for pure binomial state inputs. It is shown that the properties of the entanglement and the photon statistics of output fields are not only strongly dependent on the parameters of input binomial states but also quite involved with the nature of the beam splitter. The best entanglement can be obtained when the parameters of both input states and the beam splitter are chosen appropriately. Finally, we analyse briefly the distinguishability between the joint input state and the joint output state.     

Sommerfeld＇s Quantum Condition of Action and the Spectra of Quantum Schwarzschild Black Hole

If the situation of quantum gravity nowadays is nearly the same as that of quantum mechanics in its early time of Bohr and Sommerfeld, then a first-step study of the quantum gravity under Sommerfeld‘s quantum condition of action might be helpful. We present the spectra of quantum Schwarzschild black hole in non-relativistic quantum mechanics. It is found that the quantum of area is 8π/3 lp^2, the quantum of entropy is 2π/4kB, and the Hawking evaporation will cease when the black hole reaches the ground state m=1/2√3mp.     

Continuous Variable Entanglement and Violation of Bell Inequality for Two Modes in a Three-Level Cascade Atomic System

Continuous variable entanglement and violation of Bell inequality for two modes are investigated in a three-level cascade atomic system. Entanglement of the system is demonstrated according to the entanglement criterion [Phys. Rev. Lett. 84 （2000）2722]. Violation of Bell inequality is studied within the framework of a quantum theory of multiwave mixing. It is shown that there are some states that are entangled but do not violate the Bell inequality.     

Preparation of the W State of Atoms in a Single Cavity or N Distant Cavities by Photon Interference

We suggest two schemes to generate the W state of N A-type three-level atoms. In the schemes, identical N three-level atoms are trapped in a cavity or N distant cavities. The success or failure of the generation of the W state can be determined by detecting the polarization of photon leaking out of the cavity. The result demonstrates that the W state is free from both the cavity loss and the spontaneous emission due to the fact that the two ground states (left and right) of the three-level atoms are stable states (or metastable states).     

Teleportation of an n-bit one-photon and vacuum entangled GHZ cavity-field state

A scheme for teleporting an arbitrary n-bit one-photon and vacuum entangled Greenberger-Horne-Zeilinger （GHZ） state is proposed. In this scheme, the maximum entanglement GHZ state is used as a quantum channel. We find a method of distinguishing four Bell states just by detecting the atomic states three times, which is irrelevant to the qubit number of the state to be teleported.     

Theoretical Analysis of Ionic Autoionization Spectra of Lanthanum in the Energy Region of 90650—915—00cm^—1

Eigenquantum defects μα and transformation matrix Uiα of La are calculated from the first principles byrelativistic multichannel theory, and dipole matrix elements Dα are obtained by fitting the experimental spectra.With these parameters, ionic autoionization spectra of lanthanum via an intermediatestate (Xe)5d6d^-1 P1 of La . in the energy region of 90650-91500 cm^-1 are calculated within the framework of multichannel auantum defecttheory. Our calculated spectra are in general agreement with the experimental data.