色散吸收四端口器件的量子态变换
Quantum state transformation by dispersive and absorbing four-port devices
摘要：
最近导出的色散吸收四端口器件辐射场的输入输出关系[T。Gruner和D.- G. Welsch，Phys.Rev.A54，1661（1996）]用于导出将输出量子态与输入量子态相关联的幺正变换，包括辐射和物质，而不设置频率限制。结果表明，对于每个频率，变换可以被看作是一个良好的SU（4）群变换，可以分解为U（2）和SU（2）群变换的乘积。它们中的每一个都可以被认为是由特定的无损四端口设备实现的。如果对于远离介质共振的窄带宽辐射，可以忽略四端口器件的吸收矩阵，则可以识别出用于无损器件的众所周知的SU（2）群变换。给出了Fock态和相干态转换的显式公式。
英文摘要：
The recently derived input-output relations for the radiation field at a dispersive and absorbing four-port device [T. Gruner and D.-G. Welsch, Phys. Rev. A 54, 1661 (1996)] are used to derive the unitary transformation that relates the output quantum state to the input quantum state, including radiation and matter and without placing frequency restrictions. It is shown that for each frequency the transformation can be regarded as a well-behaved SU(4) group transformation that can be decomposed into a product of U(2) and SU(2) group transformations. Each of them may be thought of as being realized by a particular lossless four-port device. If for narrow-bandwidth radiation far from the medium resonances the absorption matrix of the four-port device can be disregarded, the well-known SU(2) group transformation for a lossless device is recognized. Explicit formulas for the transformation of Fock-states and coherent states are given.
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