102 research outputs found
Reversible Mode Switching in Y coupled Terahertz Lasers
Electrically independent terahertz (THz) quantum cascade lasers (QCLs) are
optically coupled in a Y configuration. Dual frequency, electronically
switchable emission is achieved in one QCL using an aperiodic grating, designed
using computer-generated hologram techniques, incorporated directly into the
QCL waveguide by focussed ion beam milling. Multi-moded emission around 2.9 THz
is inhibited, lasing instead occurring at switchable grating-selected
frequencies of 2.88 and 2.92 THz. This photonic control and switching behaviour
is selectively and reversibly transferred to the second, unmodified QCL via
evanescent mode coupling, without the transfer of the inherent grating losses
Y coupled terahertz quantum cascade lasers
Here we demonstrate a Y coupled terahertz (THz) quantum cascade laser (QCL)
system. The two THz QCLs working around 2.85 THz are driven by independent
electrical pulsers. Total peak THz output power of the Y system, with both arms
being driven synchronously, is found to be more than the linear sum of the peak
powers from the individual arms; 10.4 mW compared with 9.6 mW (4.7 mW + 4.9
mW). Furthermore, we demonstrate that the emission spectra of this coupled
system are significantly different to that of either arm alone, or to the
linear combination of their individual spectra.Comment: 9 pages, 3 figure
Anti-bunched photons from a lateral light-emitting diode
We demonstrate anti-bunched emission from a lateral-light emitting diode.
Sub-Poissonian emission statistic, with a g(0)=0.7, is achieved at
cryogenic temperature in the pulsed low-current regime, by exploiting electron
injection through shallow impurities located in the diode depletion region.
Thanks to its simple fabrication scheme and to its modulation bandwidth in the
GHz range, we believe our devices are an appealing substitute for
highly-attenuated lasers in existing quantum-key-distribution systems. Our
devices outperform strongly-attenuated lasers in terms of multi-photon emission
events and can therefore lead to a significant security improvement in existing
quantum key distribution systems
Quantisation of Hopping Magnetoresistance Prefactor in Strongly Correlated Two-Dimensional Electron Systems
We report an universal behaviour of hopping transport in strongly interacting
mesoscopic two-dimensional electron systems (2DES). In a certain window of
background disorder, the resistivity at low perpendicular magnetic fields
follows the expected relation . The prefactor decreases exponentially with
increasing electron density but saturates to a finite value at higher
densities. Strikingly, this value is found to be universal when expressed in
terms of absolute resistance and and shows quantisation at and . We suggest a strongly correlated
electronic phase as a possible explanation.Comment: 5 pages, 3 figures, Proceedings of EP2DS 17, Reference adde
Single-Photon Superradiance from a Quantum Dot.
We report on the observation of single-photon superradiance from an exciton in a semiconductor quantum dot. The confinement by the quantum dot is strong enough for it to mimic a two-level atom, yet sufficiently weak to ensure superradiance. The electrostatic interaction between the electron and the hole comprising the exciton gives rise to an anharmonic spectrum, which we exploit to prepare the superradiant quantum state deterministically with a laser pulse. We observe a fivefold enhancement of the oscillator strength compared to conventional quantum dots. The enhancement is limited by the base temperature of our cryostat and may lead to oscillator strengths above 1000 from a single quantum emitter at optical frequencies
Lasing in planar semiconductor diodes
We present a planar laser diode based on a simple fabrication scheme
compatible with virtually any geometry accessible by standard semiconductor
lithography technique. We show that our lasers exhibit ~1 GHz
-3dB-modulation-bandwidth already in this prototypical implementation.
Directions for a significant speed increase are discussed
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