摘要：
We examine the quantum correlation between the Mollow sidebands in the collective resonance fluorescence from a strongly driven ensemble of two-level atoms. By using the criterion proposed by Shchukin and Vogel, we show that non-Gaussian entanglement exists between the two separated sidebands. The responsible mechanism is traced to the spontaneous parametric process, in which the nonclassical correlation is established. This suggests that the collective resonance fluorescence provides a continuous source for the non-Gaussian entangled light and thus has great potentials for various applications in quantum information and quantum computation.
作者机构：
[Hu, Xiangming; Li, Xing] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, Xiangming] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
Parametric interaction of a pair of cavity fields in a near-resonantly driven atomic system is described by a bilinear Hamiltonian that decouples from atomic flip operators and is proportional to the population difference between dressed states. For proper choice of parameters, the parametric interaction is enhanced by at least two orders compared to the dispersively dressed cases. Although spontaneous emission is fed into the cavity fields, destructive interference occurs in the fluctuations of a pair of collective modes. As a result of the two factors, perfect squeezing and Einstein–Podolsky–Rosen entanglement in the output occur when the cavity relaxation rates are much larger than in the dispersive case. The mechanism is applicable to a great variety of multilevel systems and has experimental advantages in the cavity QED generation of squeezed and entangled states of light.
作者机构：
[Hu, Xiangming; Wang, Fei] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Wang, Fei] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We show that dark-state resonances can be a fundamental mechanism for the entanglement between light and matter. While two optical fields trap an ensemble of three-level Λ atoms into the dark state, the coherence is created between the two metastable states, and the two fields undergo no absorption. The trapped atoms behave like a coherently coupled two-party reservoir and act on the two fields. As a result, Einstein-Podolsky-Rosen entanglement is obtainable between the atomic ensemble and one collective field under proper parameter conditions. Long-lived atomic coherence and no need of nonclassical input light are the advantages for quantum communications between light and matter based on the present mechanism.
作者机构：
[Hu, Xiangming; Sun, Hong; Wang, Fei] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, Xiangming] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
One important class of multipartite continuous variable entanglement is described by a closed polygon, where every vertex represents one optical field and every side corresponds to the entanglement between the two connected vertices. Here we show that it is possible to obtain a scalable network of quadrangle entanglements by using multiple phase-dependent electromagnetically induced transparency. For 4,6,8,…,2n (n⩾2) mode cases the network consists of 1,9,36,…,14n2 (n−1)2 quadrangles, respectively. This suggests an efficient way of creating complex quantum networks and has great potentials for quantum information and computation.
通讯机构：
[Hu, Xiangming] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
In this paper, we show that it is possible to achieve continuous-variable entanglement of three optical fields in a four-level Y-type atomic system. The three fields are amplified through the Rabi resonances of the different driven transitions. Two fields from the V configuration are in one quantum beat and in the mixing parametric interactions with the third field from the lower transition. This yields entanglement between the pair of beat modes and the third field. The best achievable state in the output approaches the Einstein-Podolsky-Rosen entangled state.
作者机构：
[Hu, Xiangming; Zhu, Yuzhu; Wang, Fei; Shi, Wenxing] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, Xiangming] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We show that it is possible to obtain continuous variable entanglement for four optical fields via phase-dependent electromagnetically induced transparency in a four-level system in double- Λ configuration. Due to quantum interference, the four fields constitute two quantum beats, behave as a pair of collective modes, and experience high cross Kerr nonlinearities. As a result, entanglement occurs between the two collective modes and between any two individual fields from the different collective modes.
作者机构：
[Hu, Xiangming; Zhang, Xiu] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.;[Zhang, Xiu] Xiaogan Univ, Dept Phys, Xiaogan 432000, Peoples R China.
通讯机构：
[Zhang, Xiu] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We explore the quantum entanglement between two collective fields via atomic coherence effects. For three-level atoms in V configuration driven by two applied fields on two-photon resonance, one coherent superposition of the excited states is not excited, which is the counterpart of coherent population trapping. The coherence-induced depopulation makes two cavity fields in each collection combine into a quantum-beat, i.e., equivalently, the difference mode of the two components decouples from the driven atoms. The two sum modes, when they are arranged in the four-wave mixinglike interactions, can be prepared in Einstein-Podolsky-Rosen entangled state. Correspondingly, any two individual fields from different collective modes are entangled with each other. Furthermore, the effects of thermal reservoir and laser linewidths are discussed, and a generalization is given to the case in which each quantum beat involves more than two modes.
作者机构：
[Hu, Xiangming; Zhang, Liang; Kong, Lingfeng; Zhang, Xuehua] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Hu, Xiangming] H;Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
摘要：
We show that it is possible to generate a quadripartite square graph-state entanglement in two-photon resonant systems. Every vertex of the square represents an optical field and every side stands for the entanglement of the two vertices. Four optical fields of different frequencies are coupled to coherently driven three-level ladder atoms. Through such a system, quantum beats and two-photon resonant interactions combine to cause the collective-mode parametric interactions. This results in the collective-mode entanglement, which corresponds to the square graph-state entanglement of the four individual fields.
摘要：
We show that it is possible to achieve laser oscillation and two-mode entanglement by using dressed-state phase-dependent electromagnetically induced transparency (EIT) in a double Λ system. Under certain conditions, two beams of bichromatic fields induce the depopulation of a coherent superposition state of the two excited states and the quantum beat of a pair of cavity fields. While one of two beams of bichromatic fields dresses the atoms, the other and the pair of cavity fields are in phase-controlled EIT interaction with the dressed atoms. On the basis of this, the pair of cavity fields not only operates well above threshold and exhibit subshot noise but also is in an entangled state. This mechanism suggests an efficient way to achieve bright entangled source of light.
期刊：
EUROPEAN PHYSICAL JOURNAL D,2009年51(2):267-273 ISSN：1434-6060
通讯作者：
Xu, Q.
作者机构：
[Xu, Q.; Yin, J. W.] Huanggang Normal Univ, Coll Phys Sci & Technol, Huanggang 438000, Hubei, Peoples R China.;[Hu, X. M.] Huazhong Normal Univ, Dept Phys, Wuhan 430079, Peoples R China.
通讯机构：
[Xu, Q.] H;Huanggang Normal Univ, Coll Phys Sci & Technol, Huanggang 438000, Hubei, Peoples R China.
关键词：
42.50.Gy Effects of atomic coherence on propagation;absorption;and amplification of light;electromagnetically induced transparency and absorption;42.50.Hz Strong-field excitation of optical transitions in quantum systems;multiphoton processes;dynamic Stark shift
