Breaking the Limitations of Temporal Modulation via Mixed Continuity Conditions at Photonic Time Interfaces

The conventional description of time-varying media assumes that electromagnetic fields evolve according to fixed continuity conditions during parameter jumps. However, recent discussions have made it clear that such continuity conditions are not physical constraints, but are determined by the microscopic processes that underlie the modulation. However, a unified theoretical framework capable of systematically describing different continuity conditions is still lacking. By treating continuity rules as tunable parameters and incorporating them into a unified time-varying theoretical framework, the scope of time-varying metamaterials is expanded to encompass non-resonant reflectionless wave amplification without momentum bandgaps, reversible conversion between propagating waves and static fields, etc. Hence, in this work, wave phenomena previously considered impossible become attainable, opening a new dimension for controlling light–matter interactions through time-varying media.