Interference Pattern of Floquet Modes in Frequency Space

Wave-particle duality is one of the key features of quantum physics, characterized by the interference pattern. Meanwhile, Floquet spectroscopy is typically studied in the high-frequency region because the Floquet sidebands are very sharp, behaving like ’particles’ in frequency space, and no interference phenomena are observed. Here, we consider the larger quantum fluctuation region where the Floquet sidebands are broader, making interference between them possible. With the help of an optical lattice clock experimental platform and numerical simulations, such interference of Floquet modes in frequency space is clearly observed. Additionally, it exhibits many exotic phenomena, such as large Floquet sidebands between integer ones, sensitivity to the initial phase, and corresponding emergent symmetries. To analytically elucidate this, we propose the Floquet Channel Interference Hypothesis (FCIH), which surprisingly matches quantitatively well with both experimental and numerical results. Our research paves the way for developing a new type of interferometer that could be applicable to other Floquet systems.