- Bose-Einstein Condensation of Light in a Semiconductor Quantum Well Microcavity(arXiv)
Author : Ross C. Schofield, Ming Fu, Edmund Clarke, Ian Farrer, Aristotelis Trapalis, Himadri S. Dhar, Rick Mukherjee, Jon Heffernan, Florian Mintert, Robert A. Nyman, Rupert F. Oulton
Abstract : When particles with integer spin accumulate at low temperature and high density they undergo Bose-Einstein condensation (BEC). Atoms, solid-state excitons and excitons coupled to light all exhibit BEC, which results in high coherence due to massive occupation of the respective system’s ground state. Surprisingly, photons were shown to exhibit BEC much more recently in organic dye-filled optical microcavities, which, owing to the photon’s low mass, occurs at room temperature. Here we demonstrate that photons within an inorganic semiconductor microcavity also thermalise and undergo BEC. Although semiconductor lasers are understood to operate out of thermal equilibrium, we identify a region of good thermalisation in our system where we can clearly distinguish laser action from BEC. Based on well-developed technology, semiconductor microcavities are a robust system for exploring the physics and applications of quantum statistical photon condensates. Notably, photon BEC is an alternative to exciton-based BECs, which dissociate under high excitation and often require cryogenic operating conditions. In practical terms, photon BECs offer their critical behaviour at lower thresholds than lasers. Our study shows two further advantages of photon BEC in semiconductor materials: the lack of dark electronic states allows these BECs to be sustained continuously; and semiconductor quantum wells offer strong photon-photon scattering. We measure an unoptimised interaction parameter, g~=0.0023±0.0003, which is large enough to access the rich physics of interactions within BECs, such as superfluid light or vortex formation
2.Simple model for frequency response of a resonant tunneling diode caused by potential change of quantum well due to electron charge (arXiv)
Author : Masahiro Asada, Safumi Suzuki
Abstract : The frequency dependence of negative differential conductance (NDC) is an important property for the resonant-tunneling-diode terahertz source. Among several phenomena determining the frequency dependence, this paper shows that the effect of potential change of the quantum well due to electron charge can be analyzed with a simple and tractable model based on the tunneling admittance and capacitance. The result is identical to that of Feiginov’s analysis based on more fundamental equations, showing a one-to-one correspondence between the parameters of the two analyses. Similar to Feiginov’s analysis, our analysis also shows that NDC remains finite even at infinitely high frequency. It is shown in our model that this result is attributed to neglecting the tunneling time at the emitter barrier. Comprehensive analysis of the frequency dependence of NDC will be possible by incorporating the tunneling time into the present model
