Fig. 1: The topological multi-directional vortex maser.

a Illustration of topological vortex masing actions toward every direction normal to the cubic resonator. The cubic maser containing the gain medium is subjected to an optical pump from an optical fiber positioned beneath the system. Microwave vortex photons are emitting coherently in multiple directions. b Masing transition scheme: The Jablonski diagram illustrates the masing process in pentacene-doped p-terphenyl, which functions as the gain medium. Population inversion between the X and Z energy levels enables the masing transition, resulting in the emission of coherent microwave photons at approximately 1.45 GHz. c Photograph of the fabricated subwavelength cubic cavity made of dielectric strontium titanate featuring three through holes. The cylindrical pentacene crystal as gain medium is inserted into each air hole, forming a compact integrated device.