The Janus State: Strong Photon Antibunching from a Superposition of Squeezed Vacua

Abstract: Fundamental principles of quantum mechanics, such as superposition, have long been used to create nonclassical ``cat states'' from classical-like components. We push this concept into the fully quantum regime by introducing the Janus State -- a superposition of two squeezed vacuum states. Here, we report the discovery that this state, born from two photon-bunched components, exhibits strong photon antibunching. Our exact analytical theory reveals this emergent nonclassicality is driven by pure quantum interference, which suppresses two-photon events and drives the second-order coherence to $g^{(2)}(0) \approx 0.567$. This result fundamentally challenges the paradigm that antibunching requires non-Gaussian resources or post-selection. The Janus State thus constitutes a new foundational tool for quantum engineering, providing a deterministic and experimentally accessible route to generating highly nonclassical light.