Gain without inversion in semiconductor nanostructures

摘要: When Einstein showed that light amplification needed a collection of atoms in ‘population inversion’ (that is, where more than half the are an excited state, ready to emit rather absorb it) he was using thermodynamic arguments1. Later on, quantum theory predicted2,3 matter–wave interference effects inside could, principle, allow gain without inversion (GWI). The coherent conditions observe this strange effect have been generated atomic vapours4, but here we show semiconductor nanostructures can be tailored ‘artificial atom’ electron states which, for first time solid, also GWI. In experiments, conditions, typically either by coupling two levels third with strong beam2,3 or tunnel both same continuum (Fano effect5), responsible observation ‘electromagnetically induced transparency’ (EIT)6. turn, has allowed observations markedly slowed7 and even frozen8 propagation. Our GWI rooted phenomena and, from analysis absorption changes, infer slows ∼c/40 over spectral range optical appears.