Dynamics of a moving five-level atom interacting with cavity fields

We study the entanglement between a single five-level atom interacting with a one-mode cavity field in the case where the atomic motion is taken into account. The field entropy of this system is investigated under the nonresonant conditions. The effects of the detuning parameter and the atomic motion on the degree of entanglement are investigated. We show that both the detuning and atomic motion play important roles in the evolution of the von Neumann entropy and atomic populations.     

On the microcanonical ensemble for a spin system interacting with one-mode electromagnetic field

A system described by the Dicke Hamiltonian is considered. It is known that for the canonical density operator describing such a system, the internal energyU is strictly negative. On the other hand, the microcanonical density operator can be defined for an arbitrary value ofU. The thermodynamic limit for the microcanonical density operator is investigated. In the caseU<0 the obtained results are completely equivalent to those of the canonical density operator. However, in the caseU>0 it turns out that the photon density is non-zero, and that the entropy and the mean spin are independent ofU. Moreover, forU>0 the coupling constant of the Hamiltonian does not appear in any thermodynamic formula after the thermodynamic limit is performed.     

Response of an atom interacting with an arbitrarily polarized electromagnetic field

We develop the theory of interaction of the electromagnetic field and a single atom being in an arbitrary state and having an arbitrary direction of the angular momentum of the atomic electron with respect to the direction of the field polarization vector. It is shown that the atom response current has a tensor structure and depends on both the direction of the angular momentum of the atom, and the polarization vector of the external field. The tensor character of the response is determined by the externally induced anisotropic distribution of the probability density of spatial localization of the atomic electron. It is shown that the induced-anisotropy effects clarify the harmonic generation mechanism at play during the non-resonance interaction of laser radiation with atomic media. The developed theory is applied to the analysis of the problem about the generation of terahertz waves in a two-color laser field. It is shown that the change in the mutual orientation of wave polarization vectors leads to a significant increase in the efficiency of conversion of high-frequency fields to low-frequency ones. It is shown for the first time that the generation of terahertz waves is possible in the preionization regime, when the generation mechanism is related to atomic nonlinearity.     

Concurrence evolution of two qubits coupled with one-mode cavity separately

The concurrence evolution of two qubits coupled with one-mode cavity separately is investigated exactly without adopting the rotating-wave approximation. The results show that for the resonant case, the concurrence evolution behaviour of the system is similar to that of the Markovian case when the coupling strength is weak, while the concurrence vanishes in a finite time and might revive fractional initial entanglement before it permanently vanishes when the coupling strength is strong. And for the detuning case, the entanglement could periodically recover after complete disentanglement. These results are quite different from those of system subjected to Jaynes--Cummings model.     

Entropy evolution of field interacting with V-type three-level atom via intensity-dependent coupling

The entropy evolution property of a single-mode light field interacting with V-type three-level atoms via intensity-dependent coupling has been studied, and the influence of detuning of light field and initial photon number on entropy evolution of field is discussed. It is found that if detuning is relatively small and initial light field weak, the time-evolution behavior of field entropy is similar to that of Jaynes–Cummings model with single-photon transition, but in case of sufficient large detuning and strong initial light field, the time-evolution behavior of field entropy is similar to the periodic one of field entropy of Jaynes–Cummings model with two-photon transition.     

Dynamical analysis and cosmological viability of varying G and $$\Lambda $$ cosmology

The cosmological viability of varying \(G\left( t\right) \) and \(\Lambda \left( t\right) \) cosmology is discussed by determining the cosmological eras provided by the theory. Such a study is performed with the determination of the critical points while stability analysis is performed. The application of renormalization group in the ADM formalism of general relativity provides a modified second-order theory of gravity where varying \(G\left( t\right) \) plays the role of a minimally coupled field, different from that of scalar–tensor theories, while \(\Lambda \left( t\right) =\Lambda \left( G\left( t\right) \right) \) is a potential term. We find that the theory provides two de Sitter phases and a tracking solution. In the presence of matter source, two new critical points are introduced, where the matter source contributes to the universe. One of those points describes the \(\Lambda \)CDM cosmology and in order for the solution at the point to be cosmologically viable, it has to be unstable. Moreover, the second point, where matter exists, describes a universe where the dark energy parameter for the equation of state has a different value from that of the cosmological constant.     

与准Λ型四能级系统互作用光场的熵演化

研究了准Λ型四能级系统与非关联双模相干光场相互作用系统的场熵演化特性,讨论了原子初态、平均光子数及能级劈裂对场熵的影响.该系统包含了二能级原子和三能级原子与单模场相互作用情况.     

与准∧型四能级系统互作用光场的熵演化

研究了准∧型四能级系统与非关联双模相干光场相互作用系统的场熵演化特性,讨论了原子初态、平均光子数及能级劈裂对场熵的影响.该系统包含了二能级原子和三能级原子与单模场相互作用情况.     

Entanglement swapping without joint measurement via a Λ-type atom interacting with bimodal cavity field

This paper proposes a scheme for realizing entanglement swapping in cavity QED. The scheme is based on the resonant interaction of a two-mode cavity field with a ∧-type three-level atom. In contrast with the previously proposed schemes, the present scheme is ascendant, since the fidelity is 1.0 and the joint measurement isn＇t needed. And the scheme is experimentally feasible based on the current cavity QED technique.     

级联三能级原子与相干光场相互作用的场熵演化

研究了相干态光场与级联型三能级原子相互作用过程中场熵的演化特性,数值计算结果表明:场熵随时间的演化具有明显的振荡特性,并且受相干态光场强度|α|变化的影响,当|α|较小时随|α|的增大,场熵的平均值增大,当|α|大于一定值时,场熵的振荡演化出现崩塌和复苏现象,熵的平均值反而随|α|的增大而变小.     

Modification of spontaneous emission from a five-level M-type atom in coupled cavity waveguide

We study the spontaneous emission spectrum of a five-level M-type atom driven by a microwave field, in which two upper levels are coupled by the same-coupled cavity waveguide reservoir to a lower level. The spectrum behavior presents a strong non-Lorentzian shape that originates from effective quantum interference in Markovian reservoir, in which the spectral line can be significantly enhanced and eliminated by adjusting the proper parameters of the system. However, for non-Markovian reservoir, it seems that the shape of emission spectrum is quite dependent on the geometry behavior of a coupled cavity waveguide.     

Pancharatnam phase for a system of a two-level atom interacting with a quantized field in a cavity

We derive an expression for the Pancharatnam phase for the entangled state of a single two-level atom interacting with a single electromagnetic field mode in an ideal cavity with the atom undergoing either a one- or a two-photon transition. It is shown that the Pancharatnam phase explicitly contains information about the statistics of the field and atomic coherence.     

Resonant gradient force on atom interacting with laser field

The gradient force, as a function of position and velocity, is derived for a two-level atom interacting with a standing-wave laser field. Basing on optical Bloch equations, the numerical solutions for the gradient force f⊥,n (n = 0,1, 2,3,4, …) pointing in the direction of the transverse of the laser beam are given. It is shown the higher order gradient force plays important role at strong intensity (G = 64), the contribution of them can not be neglected.     

Entropy squeezing for three-level atom interacting with a single-mode field

The entropy squeezing for a three-level atom interacting with a single-model field is studied. A general definition of entropy squeezing for three-level atom is given according to entropic uncertainty relation of three-level system, and the calculation formalism of entropy is derived for a cascade three-level atom. By using numerical calculation, the entropy squeezing properties of a cascade three-level atom are examined. Our results show that, three-level atom can generate obvious entropy squeezing effect via choosing appropriate superposition state of three-level atom. Our results are meaningful for preparing three-level system information resources with ultra-low quantum noise.     

O $$(\bar \Lambda /m_c )$$ effects in tests of factorization hypothesis for heavy-hadron nonleptonic decays

In the framework of the heavy-quark effective theory, theO ( O(_QCD)) corrections are estimated in the test of factorization hypothesis forB-meson nonleptonic decays proposed by Bjorken. Similar calculations are also carried out for _b nonleptonic decays. The effects of these corrections on the estimate of theD _s -meson decay constant are discussed.     

Effect of cavity dissipation on the emission spectrum of an atom interacting with a field in the dispersive approximation

The emission spectrum of a two-level atom interacting dispersively with a single mode radiation field in the dissipative cavity is investigated. A general expression for the emission spectrum is derived. The numerical results for the initial field in coherent state are calculated. It is found that the spectrum structure is influenced significantly by the cavity damping constant \kappa , and the spectrum structure is dependent on the interaction time T when the cavity dissipation is present. Only one peak located at Ω_a appears in the atomic spectra for larger T.     

Stark效应对双模压缩真空场与原子耦合系统腔场谱的影响

研究了Stark效应对两模双光子J-C模型腔场谱的影响,推导计算出了腔场处于压缩真空态时腔场谱的计算公式和数值结果,讨论了Stark效应和初始场强对腔场谱的影响.发现初始场较弱时,Stark效应主要影响谱线的频率,对峰的强度影响不大;初始场n1=n2≥2后,Stark效应对主峰有较强的强化作用,对边峰产生抑制作用;在初始场较强时,对谱强度的影响显著.改变Stark移动参数和初始场的强度,可得到各式各样的腔场谱结构.     

利用Λ型原子与光场的纠缠态传送腔场的奇偶相干态的叠加态

根据简并Λ型三能级原子与单模光场的非共振相互作用系统的改进型有效哈密顿量，利用矩阵方法推导出任意初始情况下原子-光场系统的波函数，通过改变相互作用时间，制备出原子-腔场系统的纠缠态.提出利用原子-腔场系统的纠缠态进行概率传送腔场的奇、偶相干态的叠加态的有效方案.对于振幅很大的单模光场，通过实行Bell态测量，能成功地概率传送腔场的奇偶相干态的叠加态，其成功的总概率为0.25.