We theoretically study the few- and many-body dynamics of photons in chiral waveguides. In particular, we examine pulse propagation through an ensemble of $N$ two-level systems chirally coupled to a waveguide. We show that the system supports correlated multiphoton bound states, which have a well-defined photon number $n$ and propagate through the system with a group delay scaling as $1/n^2$. This has the interesting consequence that, during propagation, an incident coherent-state pulse breaks up into different bound-state components that can become spatially separated at the output in a sufficiently long system. For sufficiently many photons and sufficiently short systems, we show that linear combinations of $n$-body bound states recover the well-known phenomenon of mean-field solitons in self-induced transparency. Our work thus covers the entire spectrum from few-photon quantum propagation, to genuine quantum many-body (atom and photon) phenomena, and ultimately the quantum-to-classical transition. Finally, we demonstrate that the bound states can undergo elastic scattering with additional photons. Together, our results demonstrate that photon bound states are truly distinct physical objects emerging from the most elementary light-matter interaction between photons and two-level emitters. Our work opens the door to studying quantum many-body physics and soliton physics with photons in chiral waveguide QED.

中文翻译：

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手性波导QED中多体光子束缚态的动力学

从理论上讲，我们研究了手征波导中光子的少数多体动力学。特别是，我们检查了通过$ñ$两级系统手性耦合到波导。我们表明系统支持相关的多光子束缚态，该态具有明确定义的光子数$ñ$ 并通过组延迟扩展为 $\mathrm{1个}/{ñ}^2$。这具有令人感兴趣的结果，即在传播过程中，入射相干态脉冲分解为不同的束缚态分量，这些束缚态分量可以在足够长的系统中的输出处在空间上分离。对于足够多的光子和足够短的系统，我们证明了$ñ$体束缚态恢复了自感应透明中均场孤子的众所周知的现象。因此，我们的工作涵盖了从几个光子量子传播到真正的量子多体（原子和光子）现象的整个光谱，并最终涵盖了从量子到经典的跃迁。最后，我们证明了束缚态可以与其他光子发生弹性散射。总之，我们的结果表明，光子束缚态是真正不同的物理对象，它们是由光子与两能级发射器之间最基本的光-质相互作用产生的。我们的工作打开了研究手性波导QED中光子的量子多体物理学和孤子物理学的大门。