In this manuscript we analyze the emergence of protected multiphoton states in scattering problems with cylindrical symmetry. In order to do that, we first provide a formal definition of the concept of postselected symmetry-protection. We show that symmetry-protected states are not limited to one- or two-photon states, on the contrary, it can be formally extended to the multiphoton case. In addition, we prove for the case of cylindrical symmetry that all possible multiphoton protected states are constructed from a small set of one- and two-photon states. Finally, we point out possible applications that symmetry-protected states may have in quantum communications, concretely, in the construction of decoherence-free subspaces.

中文翻译：

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光的多光子态的对称保护

在这份手稿中，我们分析了圆柱对称散射问题中受保护多光子态的出现。为了做到这一点，我们首先提供后选择对称保护概念的正式定义。我们表明对称保护状态不限于单光子或双光子状态，相反，它可以正式扩展到多光子情况。此外，我们证明了圆柱对称的情况，所有可能的多光子保护状态都是由一小组单光子状态和双光子状态构成的。最后，我们指出了对称保护状态在量子通信中的可能应用，具体而言，在构建无退相干子空间方面。