Revealing non-Hermitian band structure of photonic Floquet media

Abstract

Periodically driven systems are ubiquitously found in both classical and quantum regimes. In the field of photonics, these Floquet systems have begun to provide insight into how time periodicity can extend the concept of spatially periodic photonic crystals and metamaterials to the time domain. However, despite the necessity arising from the presence of nonreciprocal coupling between states in a photonic Floquet medium, a unified non-Hermitian band structure description remains elusive. We experimentally reveal the unique Bloch-Floquet and non-Bloch band structures of a photonic Floquet medium emulated in the microwave regime with a one-dimensional array of time-periodically driven resonators. These non-Hermitian band structures are shown to be two measurable distinct subsets of complex eigenfrequency surfaces of the photonic Floquet medium defined in complex momentum space.

Non-Hermitian Floquet Topological Matter—A Review

“…On the experimental side, the quantum walks in cold atoms, photonic setups, and circuit QED provide useful frameworks to realize and detect non-Hermitian Floquet topological matter [193,194,210,[213][214][215][216]224,225,243]. Coupled resonators offer another class of setups to explore non-Hermitian Floquet topological matter, in which transient and anomalous Floquet NHSEs [182,183], Floquet PT symmetry [218], Floquet EPs and even non-Bloch Floquet band structures [306] have been experimentally studied.…”

Floquet parity-time symmetry in integrated photonics

“…Periodic driving of PT-symmetric systems breaks time translational symmetry and allows for enriched phase transitions 42 – 45 . For example, periodic modulation of the non-Hermiticity parameter was introduced in a two-level Rabi model, leading to a broken PT-symmetry phase at arbitrary levels of gain/loss 46 .…”

Conformal Spatiotemporal Modulation Enabled Geometric Frequency Combs

“…Optical frequency combs (OFCs), consisting of a train of uniformly spaced discrete spectral lines, have emerged as a vibrant and rapidly growing field in photonics and information science. , Driven by the advancement of nanofabrication technique, various platforms have been employed to generate OFCs, such as mode locked lasers − and microresonators. − Over the past decades, OFCs have been extensively investigated and demonstrated significant potential in optical spectroscopy, light detection and ranging (LIDAR), and optical communications . Owing to the breaking of time translational symmetry, temporal modulations provide an alternative approach to realize OFCs. , Distinct from uniform spatiotemporal modulations , and conventional periodic time crystals (PTCs), − the proposed conformal time-varying medium results in the generation of nonuniform OFCs, where the frequency spacings between adjacent spectral components can be flexibly tuned from quasi-uniform to geometrically progressive. Appropriately tuning of modulation speeds of spatiotemporal boundaries allows for the flexible manipulation of the spectral distribution, comb spacing, number of spectral lines, and the amplitude profiles of the designed OFCs. − In particular, the output signals can be drastically amplified through the cascaded excitation of geometric harmonics, a phenomenon similar to the luminal amplification. − Compared with linear frequency combs, the geometric comb enabled by the conformal temporal modulation can effectively suppress ambiguous peaks in its autocorrelation, , thereby leading to reverberation suppression and improved resolution for range estimation. , The broad tuning capabilities of the conformal time-varying media make the resultant OFCs suitable for various applications, particularly in the fields of spectroscopy and radar detections. , …”