Proposal for THz lasing from a topological quantum dot

Topological quantum dots (TQDs) are 3D topological insulator (TI) nanoparticles, displaying symmetry-protected surface states with discretized energies. We present a theoretical proposal to harness these energy levels in a closed lasing scheme operating in the terahertz (THz) frequency range. In this scheme, a single TQD lases from its topological surface states in the THz regime when pumped with low intensity, incoherent THz frequency light. The time scales associated with the system are unusually slow, and we find that lasing occurs with a very low threshold. THz lasers are often bulky or require intricately engineered nanostructures. Topological quantum dots present a new, compact and simple platform for THz lasing. The lasing threshold is so low, we predict that the room-temperature blackbody radiation can substantially contribute to population inversion, providing a route to room-temperature THz lasing pumped via blackbody radiation.