Abstract
We conduct theoretical studies on the effects of various parameters on generation of multipartite continuous-variable entanglement via atomic spin wave induced by the strong coupling and probe fields in the Λ-type electromagnetically induced transparency configuration in a realistic atomic ensemble by using the Heisenberg-Langevin formalism. It is shown that the increase of the atomic density and/or Rabi frequencies of the scattering fields, as well as the decrease of the coherence decay rate of the lower doublet would strengthen the degree of multipartite entanglement. This provides a clear evidence that the creation of multicolor multipartite entangled narrow-band fields to any desired number with a long correlation time can be achieved conveniently by using atomic spin wave in an atomic ensemble with large optical depth, which may find interesting applications in quantum information processing and quantum networks.
Highlights
Generating multipartite continuous-variable (CV) entanglement is a key resource for the implementation of quantum information protocols [1,2,3]
By using nondegenerate four-wave mixing (FWM) or Raman-scattering processes in an atomic ensemble, the electromagnetically induced transparency [9] (EIT)-based double- -type systems have been actively studied for efficiently creating nondegenerate quantum correlated or entangled narrow-band photon pairs [10,11,12]
Such a scheme benefits from the cancellation of resonant absorption and, at the same time, the resonant enhancement of generation efficiency for the nonlinear optical processes [13], and the correlation time is determined by the long coherence decay time (∼ ms or even ∼ s [14]) between the two lower states, thereby having the virtue suitable for quantum memory required in quantum communication [10]
Summary
Generating multipartite continuous-variable (CV) entanglement is a key resource for the implementation of quantum information protocols [1,2,3]. By using nondegenerate four-wave mixing (FWM) or Raman-scattering processes in an atomic ensemble, the electromagnetically induced transparency [9] (EIT)-based double- -type systems have been actively studied for efficiently creating nondegenerate quantum correlated or entangled narrow-band photon pairs [10,11,12] Such a scheme benefits from the cancellation of resonant absorption and, at the same time, the resonant enhancement of generation efficiency for the nonlinear optical processes [13], and the correlation time is determined by the long coherence decay time (∼ ms or even ∼ s [14]) between the two lower states, thereby having the virtue suitable for quantum memory required in quantum communication [10]. Multiple entangled Stokes and anti-Stokes fields, simultaneously produced through scattering the applied laser fields off the atomic spin wave, can be obtained by using an atomic ensemble This method can, in principle, provide an alternative way to create nondegenerate multientangled CV fields (up to an arbitrarily high order) with long correlation time, which may find interesting applications in quantum communication and quantum information processing. Two strong on-resonant fields are used to create the spin coherence in the current scheme, in comparison to the two strong far-off-resonant fields used in Ref. [16]
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