Optically induced transparency in bosonic cascade lasers

Bosonic cascade lasers are terahertz (THz) lasers based on stimulated radiative transitions between bosonic condensates of excitons or exciton-polaritons confined in a trap. We study the interaction of an incoming THz pulse resonant in frequency with the transitions between neighboring energy levels of the cascade. We show that at certain optical pump conditions the cascade becomes transparent to the incident pulse: it neither absorbs nor amplifies it, in the mean field approximation. The populations of intermediate levels of the bosonic cascade change as the THz pulse passes, nevertheless. In comparison, a fermionic cascade laser does not reveal any of these properties.Comment: 4 pages, 5 figure

Quantization of entropy in a quasi-two-dimensional electron gas

We demonstrate that the partial entropy of a two-dimensional electron gas (2DEG) exhibits quantized peaks at resonances between the chemical potential and electron levels of size quantization. In the limit of no scattering, the peaks depend only on the subband quantization number and are independent on material parameters, shape of the confining potential, electron effective mass and temperature. The quantization of partial entropy is a signature of a topological phase transition in a 2DEG. In the presence of stationary disorder, the magnitude of peaks decreases. Its deviation from the quantized values is a direct measure of the disorder induced smearing of the electronic density of states.Comment: 4 pages, 2 figure

Light Mediated Superconducting Transistor

Bose-condensation of mass-less quasiparticles (photons) can be easily achieved at the room temperature in lasers. On the other hand, condensation of bosons having a non-zero mass requires usually ultra-low temperatures. Recently, it has been shown that polaritons, which are half-light-half-matter quasi-particles, may form condensed states at high temperatures (up to 300K). Polaritons composed by electron-hole pairs coupled to confined light modes in optical cavities may form a Bardeen-Cooper-Schriefer (BCS) superfluid. We propose a new transistor based on stimulated scattering of electron-hole pairs into the BCS polariton mode. A pn-junction embedded inside an optical cavity resonantly emits light into the cavity mode. If the cavity mode energy slightly exceeds the band-gap energy, it couples with electron-hole pairs with zero centre of mass wave-vector but non-zero wave-vector of relative motion. This creates a super-current in the plane of the structure. In an isotropic case, its direction is chosen by the system spontaneously. Otherwise, it is pinned to the external in-plane bias. We calculate the phase diagram for the electron-hole-polariton system.Comment: 11 pages, 3 figure

Superradiant terahertz emission by dipolaritons

Dipolaritons are mixed light-matter quasiparticles formed in double quantum wells embedded in microcavities. Due to resonant coupling between direct and indirect excitons via electronic tunnelling, dipolaritons possess large dipole moments. Resonant excitation of the cavity mode by a short pulse of light induces oscillations of the indirect exciton density with a characteristic frequency of Rabi flopping. This results in oscillations of classical Hertz dipoles array which generate supperradiant emission on a terahertz (THz) frequency. Resulting THz signal may be enhanced using the supplementary THz cavity in the weak coupling regime.Comment: 5+10 pages, 3+5 figures; close to printed version, to appear in Phys. Rev. Let