论文标题
通过$ \ Mathcal {pt} $ - 对称系统的光传播的基本问题
Fundamental issues with light propagation through $\mathcal{PT}$-symmetric systems
论文作者
论文摘要
我们分析了su-schrieffer--heeger（ssh）平等时代（$ \ Mathcal {pt} $）对称链中非物质静物群速度的出现，并探索了这种行为的起源。通过将无限损耗的SSH链与一维bragg堆栈的频带结构进行比较，我们首先在紧密结合描述中排除了不足的耦合考虑因素，这是群体速度差异的原因。然后，我们专注于材料分散，并表明，在描述有损和增益组件的描述中，恢复因果关系可以解决该问题并恢复有限的群体速度，当伴随着重要的想象部件时，其实际部分只能超过真空中的光速。我们的分析引入了常见$ \ Mathcal {pt} $ - 对称系统所需的实际限制。
We analyse the emergence of unphysical superluminal group velocities in Su--Schrieffer--Heeger (SSH) parity-time ($\mathcal{PT}$) symmetric chains, and explore the origins of such a behaviour. By comparing the band structure of an infinite loss-gain SSH chain with that of a one-dimensional Bragg stack, we first exclude insufficient coupling consideration in the tight-binding description as the cause of group-velocity divergence. We then focus on material dispersion, and show that indeed, restoring causality in the description of both the lossy and the gain components resolves the problem and recovers finite group velocities, whose real part can only exceed the speed of light in vacuum when accompanied by a significant imaginary part. Our analysis introduces thus the required practical limits in the performance of common $\mathcal{PT}$-symmetric systems.
