By applying a third mixing field E m1 (with frequency ω m 1 and Rabi frequency Ω m 1), off-resonantly coupled to levels |1〉 and |3〉, a Stokes field E 1 can be created through the nondegenerate FWM process 13, 14. A strong coupling field E c (with frequency ω c and Rabi frequency Ω c) and a relatively weak probe field E p (with frequency ω p and Rabi frequency Ω p) are tuned to be on resonance with the transitions |2〉–|3〉 and |1〉–|3〉, respectively. 1a, where energy levels |1〉, |2〉 and |3〉, forming the three-level Λ-type system, correspond, respectively, to the ground-state hyperfine levels 5S 1/2 (F = 2), 5S 1/2 (F = 3) and the excited state 5P 1/2 in D 1 line of the 85Rb atom with the ground-state hyperfine splitting of 3.036 GHz. 8, since, in principle, any desired number of entangled fields can be produced through this entangler. Also, this proposal is different from the one proposed in Ref. Here, the entanglement features between the atomic ensemble and the generated fields are investigated and it is shown that under the EIT condition the generated atomic spin wave can serve as an entangler. Moreover, the present proposal is different from the previously proposed ones as given in Refs. This proposed entangler is quite distinct as compared to the conventional PBS entangler 23, 24, 25, since only coherent input light fields are needed for generating multipartite entanglement in the present scheme, whereas nonclassical input light fields are required when using the PBS entangler. Through stimulated Raman scattering processes, nondegenerate narrow-band multi-entangled fields up to any desired number can, in principle, be achieved via such an entangler. The atomic spin wave, which can be described by a Bose operator and acts as the entangler, is produced through EIT in the Λ-type atomic configuration. In this study, we propose an efficient and convenient scheme for quantum entangler via EIT in an atomic ensemble. Moreover, generations of entanglements between an atomic ensemble and light fields, as well as between two atomic ensembles, have also been realized 8, 19, 20, 21, 22, which are vital for storage and processing of quantum information. The multicolor multipartite continuous-variable (CV) entanglement has also been achieved by using the multi-order coherent Raman scattering 18 or multiple nondegenerate FWM processes 13, 14. 8, the electromagnetically induced transparency 15, 16, 17 (EIT)-based double-Λ-type atomic system has been actively implemented for efficiently creating nondegenerate entangled twin fields through either nondegenerate four-wave mixing (FWM) or Raman scattering processes 9, 10, 11, 12. Based on the seminal proposal of Duan et al. Apart from the conventional way of generating multipartite entanglement by mixing squeezed fields created through parametric down-conversion processes in nonlinear optical crystals with linear optical elements, i.e., polarizing beam splitters (PBS) 4, 5, 6, 7 as entanglers, the atomic ensembles provide an alternative avenue to the generation of multi-entangled fields due to the virtue of narrow bandwidth, nondegenerate frequencies and long correlation time 8, 9, 10, 11, 12, 13, 14. So far, the majority studies on entanglement have dealt with the generations of multiple entangled light fields. In facilitating quantum information processing and quantum networks, generations of light-light, atom-atom and atom-light multipartite entanglements play essential roles in the implementations of quantum information protocols 1, 2, 3. As is well known, light is the best long-distance quantum information carrier and the atomic ensembles can provide the promising tools for quantum information manipulation and storage. Quantum state exchange between light and matter is a basic component for quantum interface in quantum information processing. This scheme holds great promise for applications in scalable quantum communication and quantum networks. With such an entangler, any desired number of nondegenerate narrow-band continuous-variable entangled fields, in principle, can be generated through stimulated Raman scattering processes. The atomic spin wave, produced through EIT in the Λ-type atomic system, can be described by a Bose operator and can act as an entangler. Here, we present a proof-of-principle demonstration of an efficient and convenient way to entangle multiple light fields via electromagnetically induced transparency (EIT) in an atomic ensemble. However, nonclassical input light fields are required and the generated entangled fields are always degenerate in such case. One of the commonly-used methods to generate multiple entangled fields is to employ polarizing beam splitters. Quantum entanglement plays an essential role in quantum information processing and quantum networks.
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