Recent progress on quantum state engineering has enabled the preparation of quantum photonic systems comprising multiple interacting particles. Interestingly, multiphoton quantum systems can host many complex forms of interference and scattering processes that are essential to perform operations that are intractable on classical systems. Unfortunately, the quantum coherence properties of multiphoton systems degrade upon propagation leading to undesired quantum-to-classical transitions. Furthermore, the manipulation of multiphoton quantum systems requires nonlinear interactions at the few-photon level. Here, we introduce the quantum van Cittert-Zernike theorem to describe the scattering and interference effects of propagating multiphoton systems. This fundamental theorem demonstrates that the quantum statistical fluctuations, can be modified upon propagation in the absence of conventional light-matter interactions. The generality of our formalism unveils the conditions under which the evolution of multiphoton systems can lead to surprising photon statistics modifications. Specifically, we show that the implementation of conditional measurements may enable the all-optical preparation of multiphoton systems with attenuated quantum statistics below the shot-noise limit. Remarkably, this effect cannot be explained through the classical theory of optical coherence. As such, our work opens new paradigms within the established field of quantum coherence.

量子态工程的最新进展使得能够制备包含多个相互作用粒子的量子光子系统。有趣的是，多光子量子系统可以承载许多复杂形式的干涉和散射过程，这些过程对于执行在经典系统上难以处理的操作至关重要。不幸的是，多光子系统的量子相干特性在传播时会降低，导致不希望的量子到经典跃迁。此外，多光子量子系统的操纵需要在少光子水平上的非线性相互作用。在这里，我们引入量子 van Cittert-Zernike 定理来描述传播多光子系统的散射和干涉效应。这个基本定理证明了量子统计涨落，在没有传统的光-物质相互作用的情况下，可以在传播时进行修改。我们的形式主义的普遍性揭示了多光子系统的进化可能导致令人惊讶的光子统计修改的条件。具体来说，我们表明，条件测量的实施可以实现多光子系统的全光学制备，其衰减量子统计低于散粒噪声极限。值得注意的是，这种效应无法通过光学相干的经典理论来解释。因此，我们的工作在既定的量子相干领域内开辟了新范式。我们的形式主义的普遍性揭示了多光子系统的进化可能导致令人惊讶的光子统计修改的条件。具体来说，我们表明，条件测量的实施可以实现多光子系统的全光学制备，其衰减量子统计低于散粒噪声极限。值得注意的是，这种效应无法通过光学相干的经典理论来解释。因此，我们的工作在既定的量子相干领域内开辟了新范式。我们的形式主义的普遍性揭示了多光子系统的进化可能导致令人惊讶的光子统计修改的条件。具体来说，我们表明，条件测量的实施可以实现多光子系统的全光学制备，其衰减量子统计低于散粒噪声极限。值得注意的是，这种效应无法通过光学相干的经典理论来解释。因此，我们的工作在既定的量子相干领域内开辟了新范式。