May 2014

Abstracts of the QSIT Lunch Seminar, Wednesday May 7, 2014

Hybrid Microwave Cavity Heat Engine

Björn Sothmann, Département de Physique Théorique, Université de Genève

We propose and analyze the use of hybrid microwave cavities as quantum heat engines. A possible realization consists of two macroscopically separated quantum dot conductors coupled capacitively to the fundamental mode of a microwave cavity. We demonstrate that an electrical current can be induced in one conductor through cavity-mediated processes by heating up the other conductor. The heat engine can reach Carnot efficiency with optimal conversion of heat to work. When the system delivers the maximum power, the efficiency can be a large fraction of the Carnot efficiency. The heat engine functions even with moderate electronic relaxation and dephasing in the quantum dots. We provide detailed estimates for the electrical current and output power using realistic parameters.

C. Bergenfeldt, P. Samuelsson, B. Sothmann, C. Flindt and M. Büttiker, Phys. Rev. Lett. 112, 076803 (2014).

Transport in quantum dash cascade laser structures

Gian Lorenzo Paravicini-Bagliani, Optoelectronics group, ETH Zurich

co-authors: V. Liverini, F. Valmorra, G. Scalari, F. Gramm and J. Faist

The injection efficiency from 2D- to 0D-confined nanostructures is of high importance to achieve inversion in quantum dot cascade lasers [1,2]. We perform magneto-tunnelling spectroscopy [3] of a double barrier InAs quantum dash resonant tunnelling diode, in order to understand the injection of carriers into the upper laser state in the dash [4]. Experimentally, we observe that the k-space wavefunction overlap of the 2D injector state and the upper lasing state in the quantum dash strongly influences the injected current. In the presence of strong in-plane magnetic fields, the overlap factor can be changed significantly to realize a current injection enhanced by several A/cm2. An improved current-voltage characteristic is also found for the corresponding laser structure in the B-field.

References:

[1] Suris 1996, NATO ASI Ser., Ser. E 323, 197
[2] Liverini et al. 2012 APL 101, 261113
[3] Vdovin et al. 2000 Science 290 12
[4] Paravicini-Bagliani et al. 2014, To be submitted