Spontaneous emission from a ladder three-level atom in anisotropic photonic crystals

We investigate the spontaneous radiation from a ladder three-level atom embedded in a three-dimensional anisotropic photonic crystal with an external driving field. The properties of the spontaneous emission are dependent strongly on the relative position of the middle level from the band edge. Due to the Autler-Townes splitting by the action of the driving field, the external driving field can also affect the properties of the spontaneous emission. The population exchanged between the upper and the middle levels decreases as the detuning of the external driving field frequency from the corresponding transition frequency increases. The properties of the emission field can be changed or so much as controlled by choosing suitable intensity of the external driving field. The emission spectrum is more complex, and dependent on the location of the observer in this case.     

Spontaneous emission spectra of a four-level atom in photonic crystals driven by two coherent fields

We investigate the spontaneous emission spectra of a four-level tripod-type atom embedded in a photonic crystal and driven by two coherent fields. It is found that due to the quantum interference caused by two driving fields, the spontaneous emission spectra have different features from the case of only one driving field. The spectra are sensitively dependent on the detuning of the driving fields. A dark line occurs for some particular initial states. By appropriately adjusting the external driving fields, the spectral-line can be narrowed, enhanced or suppressed.     

Influence of detuning on the spontaneous emission of a driven four-level atom embedded in photonic crystals

We study the spontaneous emission of a four-level atom with two transitions coupled to a reservoir that has a photonic bandgap near the band edge. Moreover, the transition from the upper level to an auxiliary level is driven by a laser. Considering the different detuning of the external driving field, we discuss some effects, such as a laser-induced dark line, a laser-induced line splitting, and a laser-induced pushing of a dressed state out of the bandgap, which originate from the quantum interference effect and control of the external driving field.     

驱动场作用下光子晶体中三能级原子的自发发射

讨论了在双光子驱动场作用下,三能级原子在光子晶体中的自发发射问题．由于量子干涉和光的局域化作用,两个上能级中的占据数将具有周期振荡或准周期振荡的性质,这不仅依赖于两个上能级与禁带的相对位置,同时也依赖于原子的初始状态,而且还与驱动场的强度、驱动场的入射位相有关．这些性质既与真空中带有驱动场的原子的自发发射性质不同,也有别于无驱动场作用下光子晶体中三能级原子的自发发射性质． 关键词：     

倒Y型四能级量子系统中亚光速和超光速传播现象的转换研究

研究了探测场、耦合场和驱动场三场作用下倒Y型四能级量子系统的光学特性,利用数值模拟的方法探讨了外加相干驱动场的拉比频率和失谐量变化时系统对探测光场吸收特性的影响. 通过绘制三维立体图,发现了探测光场的群速度在电磁诱导透明窗口处的变化规律,并且选择合适的驱动场拉比频率和失谐量,可以在理论上实现亚光速和真空光速以及超光速传播之间的转换. 关键词： 倒Y型四能级 群速度 超光速传播 亚光速传播     

Spontaneous emission properties of a driven five-level atom embedded in photonic crystals

The spontaneous emission spectra of a five-level double tripod-type atom embedded in photonic crystals (PCs) are investigated by means of two external fields driving different atomic transitions. We find that due to the quantum interference effects caused by two driving fields, the spontaneous emission spectra exhibit different features from the case of only one driving field. The influences of the parameters of two external driving fields, photonic band-gap (PBG), as well as the atomic initial states on the spectra are analyzed in detail. It is shown that some interesting phenomena such as spectral-line enhancement, spectral-line suppression, spectral-line narrowing, the appearance of dark lines, and multi-peak structures can be observed in the spectra by appropriately modulating the available system parameters. These investigations may find applications in high-precision spectroscopy.     

Reconfigurable dynamic all-optical chaotic logic operations in an optically injected VCSEL

In a chaotic system of vertical cavity surface emitting laser(VCSEL) with external optical-injection, we propose a novel implementation scheme for reconfigurable dynamic all-optical chaotic logic operations(AOCLOs). Under different key parameters, such as the bias current, the injection strength and the frequency detuning of the injected light field and the VCSEL, we also explore the evolutions of the polarization-bistability with the amplitude of the injected light field when the output of VCSEL is chaotic wave. According to the dynamic evolutions, we find out the optimal value of the frequency detuning that is considered as a control logic signal, and further implement different AOCLOs, such as AND, NAND, OR,NOR, XOR, and XNOR, by controlling the logic operation of the control logic signal between two logic inputs. Moreover,the ability to reconstruct these logic operations is demonstrated under relatively low noise strength of the spontaneous emission.     

Quantum statistics of phonon radiations in optomechanical systems

We study the correlation statistics of phonon radiations in a weakly driven optomechanical system. Three dominated scattering processes are identified by the scattering theory analytically and the master equation numerically, whose interplay determines the phonon statistical properties. Our results show that for the large detuning, the driving field off-resonant with the system induces a small emission rate of two anti-bunched phonons. For the resonant driving field, there is a relatively large emission rate of two bunched phonons.     

Stationary entanglement between two spatially separated atoms driven by a coherent laser field

This paper studies quantum entanglement between two spatially separated atoms driven by a coherent laser field in the dissipative process of spontaneous emission. It is shown that the entanglement strongly depends on the detuning of the laser frequency from atomic transition frequency, the interatomic separation and the Rabi frequency of the coherent laser field. A considerable amount of steady state entanglement can be obtained near Δ=-α (i.e., the dipole--dipole interaction and the detuning cancel out mutually) for small atomic separation and large Rabi frequency of the coherent laser field.     

Spontaneous Emission from the Ground Atomic State due to Its Crossing with the Dynamic Stark Level

The ground state of the driven three-level atomic system becomes unstable as a result of its spontaneous decay to the dynamic Stark level when the last one falls below this state. Different peculiarities of the atomic response may appear depending on the intensity and detuning of the driving field providing such level crossing.     

原子自发辐射中偶极矩的涨落与最大纠缠态的保持

研究了二能级原子与电磁场相互作用体系的自发辐射与量子纠缠态.在原子的自发辐射过程中,其偶极矩的期待值总是零,但偶极矩的涨落恒等于一个不为零的常量,因此原子的自发辐射是由真空起伏导致偶极矩的涨落引起的.Jaynes-Cummings模型是产生量子纠缠态的重要体系,研究发现,原子与场纠缠态的信息熵和纠缠度随时间作周期性的振荡,量子态在非纠缠与纠缠态之间变化.更为重要的是,在失谐量适当时,量子态将长时间停留在最大纠缠态.     

压缩真空中梯形三能级原子的辐射压力

研究了压缩真空中梯形三能级原子在单色行波场中的辐射压力。从系统的哈密顿量出发,利用玻因-马尔可夫近似,推导出了原子的光学布洛赫方程。此时用数值方法求得布洛赫方程的稳态解,然后用图示法考察了原子的辐射压力随双光子失谐、拉比频率、自发发射率等参量的依赖关系。结果表明：单光子跃迁和双光子跃迁可导致辐射压力出现各自的多普勒位移共振峰;辐射压力表现出较宽的失谐范围且强烈依赖于压缩参量以及压缩真空和相干光之间的相位关系。当相位满足匹配条件时,辐射压力减小。     

Two-atom spontaneous emission in a detuned damped cavity

By using a new technique developed recently exact closed equations of motion for expectation values for spontaneous emission from two two-level atoms in a detuned damped cavity are derived. These equations are solved numerically for different values of the cavity damping and detuning. It is pointed out that the spontaneous emission is inhibited if the cavity is detuned. Moreover, by comparing the result of the single-atom case with that of the two-atom case it is shown that the collective effects can be suppressed by changing the cavity damping and detuning.     

Concentration of Unknown Atomic Entangled States via Entanglement Swapping through Raman Interaction

We show that entanglement concentration of unknown atomic entangled states is achieved via the implementation of entanglement swapping based on Raman interaction in cavity QED. A maximally entangled state is obtained from a pair of partially entangled states probabilistically. Due to Raman interaction of two atoms with a cavity mode and an external driving field, the influence of atomic spontaneous emission has been eliminated. Because of the virtual excitation of the cavity mode, the decoherence of cavity decay and thermal field is neglected.     

Analysis of the gain and noise characteristics of fibre Brillouin amplifiers

A theoretical analysis is performed of the transfer characteristics, gain, amplified spontaneous emission noise, on/off ratio and nonlinear phase shift of a fibre Brillouin amplifier, taking into account a possible signal detuning from the line centre and the nonlinear pump power depletion effect. Among other features, it is shown that the amplified spontaneous emission noise is reduced at higher signal levels and that detuning the signal reduces the amplifier gain in the linear regime and increases the spontaneous noise power in the saturation regime. As a consequence, the on/off ratio is significantly degraded by such an effect.     

Geometric phase gate with trapped ions in thermal motion by adiabatic passage

We propose a scheme for implementing two-qubit geometric phase gate via the adiabatic evolution for trapped ions in thermal motion, leveraging on the stimulated Raman adiabatic passage with the geometric phase mechanism. Evolution along a dark state makes our scheme not only immune from decoherence due to spontaneous emission from excited states, but also rid off the dynamical phase. Furthermore, due to the opposite detuning of the driving lasers, the vibrational states of the trapped ions are only virtually excited during the operations, so our scheme is also insensitive to the occupation number of the vibrational mode.     

Continuously tunable sub-half-wavelength localization via coherent control of spontaneous emission

We propose a continuously tunable method of sub-half-wavelength localization via the coherent control of the spontaneous emission of a four-level Y-type atomic system,which is coupled to three strong coupling fields including a standing-wave field together with a weak probe field.It is shown that the sub-half-wavelength atomic localization is realized for both resonance and off-resonance cases.Furthermore,by varying the probe detuning in succession,the positions of the two localization peaks are tuned continuously within a wide range of probe field frequencies,which provides convenience for the realization of sub-half-wavelength atomic localization experimentally.     

Generation of cluster-type entangled squeezed vacuum states

We present a scheme to prepare cluster-type entangled squeezed vacuum states （CTESVS） by considering the two-photon interaction between a two-level atom and a high-quality cavity, driven by a strong classical field. After the realization of simple atomic measurements, the generation of CTESVS in four separate cavities is accomplished within the cavity decay time. In the case of large atom=cavity detuning, the scheme is immune to the effect of atomic spontaneous emission.     

Two-photon cooperative emission in the presence of athermal electromagnetic field

The possibility of cooperative spontaneous two-photon emission of an extended radiators system and the influence of the external thermal electromagnetic field on the spontaneous emission rate, in such a system, are investigated. It is concluded that, in an external electromagnetic field, the two-photon cooperative emission rate increases significantly. The importance of this effect on the emission of gamma rays from inverted long-lived isomers triggered by X-ray thermal fields, is emphasized. This revised version was published online in August 2006 with corrections to the Cover Date.     

Multiple relaxation and inhomogeneous broadening in resonance enhanced Raman scattering: Application to tunable infrared generation

The solutions for the imaginary susceptibility of the Raman field transition with arbitrary relaxation rates and field strengths are examined for differeing sets of relaxation rates with emphasis on alkali metal vapors which have spontaneous emission dominated relaxation. The model is further expanded to include Doppler broadening and used to predict the peak gain as a function of detuning for a frequency doubled alexandrite laserpumped cesium vapor gain cell.This work was supported by an Alfred P.Sloan Fellowship and a grant from the National Aeronautics and Space Administration (NAG-5-526)