标题： 双光子共振荧光的阶梯型原子系统 显示英文标题

标题： Two-Photon Resonance Fluorescence of a Ladder-Type Atomic System

摘要： 多光子发射器是量子光子学中一种备受追捧的资源。多能级原子系统与相干驱动之间的非线性相互作用可能导致共振双光子发射，但由于涉及的振子强度较小，从这一过程中获取光仍然是一项挑战。在此，我们研究了使用超导阶梯型人工原子——transmon——强耦合到波导中的微波频率下的双光子共振荧光。我们以越来越高的功率驱动基态和第二激发态之间的双光子跃迁，并观察到一个强度可与单光子发射相比的共振荧光峰，直到它分裂成类似Mollow的三重态。我们测量了频率过滤后的光谱线的光子关联，发现尽管基频发射保持反聚束，双光子跃迁处的共振荧光峰则表现出极好的聚束。我们的结果为在微波领域实现多光子源提供了一条途径。 显示英文摘要

摘要： Multi-photon emitters are a sought-after resource in quantum photonics. Nonlinear interactions between a multi-level atomic system and a coherent drive can lead to resonant two-photon emission, but harvesting light from this process has remained a challenge due to the small oscillator strengths involved. Here we present a study of two-photon resonance fluorescence at microwave frequencies, using a superconducting, ladder-type artificial atom, a transmon, strongly coupled to a waveguide. We drive the two-photon transition between the ground and second-excited state at increasingly high powers and observe a resonance fluorescence peak whose intensity becomes comparable to single-photon emission until it splits into a Mollow-like triplet. We measure photon correlations of frequency-filtered spectral lines and find that while emission at the fundamental frequency stays antibunched, the resonance fluorescence peak at the two-photon transition is superbunched. Our results provide a route towards the realization of multi-photon sources in the microwave domain.