March 2019

Abstracts of the QSIT Lunch Seminar, Thursday, March 7, 2019

Electrically pumped phonon-polariton lasers

Martin Franckie - Quantum Optoelectronics Group (Faist group), ETH Zurich

Phonons are quantized lattice vibrations that can interact strongly with both electrons and light in polar crystalline materials, such as III-V semiconductors. Especially the transverse optical phonon mode couples strongly to light, forming collective excitations called phonon-polaritons which display novel quantum properties. In contrast to previous studies of phonon-polaritons, which were generated by optical pumping, our presented phonon-polariton laser devices feature coherent generation of phonon-polaritons directly by stimulated emission from an electrically pumped inverted intersubband system. This has several advantages, such as a much more efficient generation, the possibility for optical lasing in the phonon Restrahlen band, as well as device integration on very small scales for the use in e.~g.~non-linear optical processes and sensing applications. In this talk, I will explain the physical principle and model behind the phonon-polariton laser, as well as show experimental data highlighting the polaritonic nature of the emission in a regime where the phonon constitutes up to 65% of the polariton.

Cotunnelling in electronic dot—cavity systems

Michael Ferguson - Quantum Condensed and Coherent Systems (Blatter group), ETH Zurich

Strong coupling between an electronic cavity and a quantum dot has been recently demonstrated [Phys. Rev. Lett. 115, 166603 (2015)] and described in a comprehensive theoretical framework [Phys. Rev. B 96, 235431 (2017)]. Here, we focus on the signatures that demonstrate the cavity's impact on coherent cotunnelling processes in the Coulomb blockade regime. We find that the original dot-cavity model also correctly describes the transport signatures associated with the blockade regime. Our minimal model for the dot—cavity setup thus provides a complete understanding of all the experimentally observed transport signatures. We use exact diagonalisation for the dot—cavity system and determine the rates entering the master equation perturbatively. Given the exact treatment of the dot—cavity system, a lowest order treatment of the lead-dot—cavity coupling already suffices to describe all cavity-assisted cotunnelling processes.