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A surface-acoustic-wave (SAW) driven light-emitting-diode structure that can implement a single-photon source for quantum-cryptography applications is demonstrated. Our lateral n-i-p junction is realized starting from an undoped GaAs/AlGaAs quantum well by gating. It incorporates interdigitated transducers for SAW generation and lateral gates for current control. We demonstrate acoustoelectric transport and SAW-driven electroluminescence. The acoustoelectric current can be controlled down to complete pinch-off by means of the lateral gates. [ABSTRACT FROM AUTHOR]

The authors report the external control of the polariton ground state by manipulating the coupling between the intersubband transition and the photonic mode of a GaAs/AlGaAs microcavity. The vacuum-field Rabi splitting is varied by means of charge transfer between the energetically-aligned ground subbands of asymmetric tunnel-coupled quantum wells. The authors propose the use of this structure concept for implementing ultrafast modulation of intersubband polaritons. [ABSTRACT FROM AUTHOR]

We demonstrate the external control of the coupling between the intersubband transition and the photonic mode of a GaAs/AlGaAs microcavity with multiple quantum wells embedded. By electrical gating, the charge density in the wells can be lowered, thereby quenching the intersubband polaritons and reverting the system to uncoupled excitations. The angle-dependent reflectance measurements are in good agreement with theoretical calculations performed in the transfer matrix formalism. The experiment shows the prospects offered by intersubband microcavities through manipulation of the system ground state. [ABSTRACT FROM AUTHOR]

When two separately contacted quantum Hall (QH) edge channels are brought into interaction, they can equilibrate their imbalance via scattering processes. In this work, we use a tunable QH circuit to implement a junction between copropagating edge channels, the length of which can be controlled with continuity. Such a variable device allows us to investigate how current-voltage characteristics evolve when the junction length d is changed. Recent experiments with fixed geometry reported a significant reduction of the threshold voltage for the onset of photon emission, the origin of which is still under debate. Our spatially resolved measurements reveal that this threshold shift depends on the junction length. We discuss this unexpected result on the basis of a model that demonstrates that a heating of electrons is the dominant process responsible for the observed reduction of the threshold voltage. [ABSTRACT FROM AUTHOR]

Inter-edge tunneling in the fractional quantum Hall regime at temperatures down to 20 mK is investigated by using split-gate constrictions to induce a controllable scattering between the edges. Both weak- and strong-backscattering regimes are explored. Tunneling characteristics as a function of split-gate bias as well as temperature are measured and compared with available theories. [Copyright &y& Elsevier]