Proposal for THz lasing from a topological quantum dot

Topological quantum dots (TQDs) are 3D topological insulator nanoparticles with radius below 100 nm, which display symmetry-protected surface states with discretized energies. We propose a scheme which harnesses these energy levels in a closed lasing scheme, in which a single TQD, when pumped with incoherent THz light, lases from its surface states in the THz regime. The time scales associated with the system are unusually slow, and lasing occurs with a very low threshold. Due to the low threshold, we predict that blackbody radiation at room-temperature provides enough photons to pump the system, providing a route to room-temperature THz lasing with blackbody radiation as the pump.