Parity-Time (PT$\mathcal{P}\mathcal{T}$) symmetry has become an important concept in the design of synthetic optical materials, with exotic functionalities such as unidirectional transport and nonreciprocal reflection. At exceptional points, this symmetry is spontaneously broken, and solutions transition from those with conserved intensity to exponential growth or decay. Here, we analyze a quantum-photonic surface formed by a single layer of atoms in an array with light mediating strong cooperative many-body interactions. We show how delocalized collective excitation eigenmodes can exhibit an effective PT$\mathcal{P}\mathcal{T}$ symmetry and nonexponential decay. This effective symmetry is achieved in a passive system without gain by balancing the scattering of a bright mode with the loss from a subradiant dark mode. These modes coalesce at exceptional points, evidenced by the emergence of coherent perfect absorption where coherent incoming light is perfectly absorbed and scattered only incoherently. We also show how PT$\mathcal{P}\mathcal{T}$ symmetry can be generated in total reflection and by balancing scattering and loss between different polarizations of collective modes.

中文翻译：

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协同原子响应中的奇偶时间对称和相干完美吸收

奇偶时间（PT $ \ mathcal {P} \ mathcal {T} $）对称性已成为合成光学材料设计中的重要概念，具有奇特的功能，如单向传输和不可逆反射。在某些特殊情况下，这种对称性自然破裂，溶液从强度守恒的溶液过渡到指数增长或衰减的溶液。在这里，我们分析了由单原子层构成的量子光子表面，该光层具有强的协同多体相互作用。我们展示了离域的集体激发本征模式如何表现出有效的PT $ \ mathcal {P} \ mathcal {T} $对称性和非指数衰减。这种有效的对称性是在无增益的无源系统中实现的，它通过平衡亮模式的散射与亚辐射暗模式的损耗来实现平衡。这些模式在特殊点合并，这由相干完美吸收的出现来证明，其中相干入射光被完美吸收并且仅非相干地散射。我们还展示了如何在全反射中以及通过平衡集体模式的不同极化之间的散射和损耗来生成PT $ \ mathcal {P} \ mathcal {T} $对称性。