Abstract. In spontaneous Raman scattering in an atomic ensemble, a collective atomic spin wave is created in correlation with the Stokes field. When the Stokes photons from two or more such atomic ensembles are made indistinguishable, a 'which-way' collective atomic spin excitation is generated among the independent atomic ensembles. We demonstrate this phenomenon experimentally by reading out the atomic spin excitations and observing interference between the read-out beams. When a single-photon projective measurement is made on the indistinguishable Stokes photons, this simple scheme can be used to entangle independent atomic ensembles. Compared to other currently used methods, this scheme can be easily scaled up and has greater efficiency.

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By using the Moore-Penrose inverse and the singular value decomposition theory, in this paper, the author designed controllers make the eigenvalues of the closed -loop system located in a ring of the unit circle, and the variance of each steady state compose to the given constraint. And author derives the existing sufficient and necessary conditions and the expression of solution by a modified algebraic Lyapunov matrix equation. The corresponding numerical example explains this method designed in practical engineering control system possible.

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