11 October 2013

COBRA COLLOQUIUM: Friday October 11, 2013 at 15:00 – 16:00 Auditorium room 13 !!!

Speaker: Prof. Dr. Armando Rastelli

Title: Strain-tunable quantum optoelectronic devices

Abstract: Optically active semiconductor quantum dots (QDs) confine the motion of charge carriers in three-dimensions and are thus often referred to as "artificial atoms". Research on such systems is partly driven by prospects of using them as building blocks for quantum communication devices. However, unlike real atoms, the structural properties of QDs are affected by unavoidable fluctuations, which make it difficult to obtain QDs with precisely defined electronic and optical properties. To alleviate this problem, we have introduced QD-based devices in which the semiconductor structures are integrated on top of piezoelectric actuators made of PMN-PT material [1]. This combination allows us to reversibly change the strain in the semiconductor (within about ±0.2%) and hence to use (anisotropic) strain fields as a “tuning knob” to modify in a broad range the electronic and optical properties of embedded QDs. In this seminar I will illustrate how strain-induced effects can be used to realize wavelength-tunable, electrically-driven sources of triggered single photons [2,3], to make any QD suitable for the generation of polarization-entangled photon pairs (independent on its structural properties [4]) and to tune the binding energies of different excitonic complexes confined in QDs [5].
[1] A. Rastelli et al. Phys. Stat. Solidi 249, 687 (2012)
[2] R. Trotta et al. Adv. Mater. 24, 2268 (2012)
[3] J.X. Zhang et al. (2013) 
[4] R. Trotta et al. Phys. Rev. Lett. 109, 147401 (2012); R. Trotta et al. (2013)
[5] R. Trotta et al. Phys. Rev. B (in press)

Biography: Armando Rastelli studied Physics at the Universities of Bologna and Camerino, Italy from 1993 until 1998 and carried out his "Laurea" degree thesis at the Gran Sasso National Laboratory. In 2003 he received the PhD degree in Physics from the University of Pavia for his work on the epitaxial growth and structural properties of SiGe nanostructures, accomplished between 2000 and 2002 at the ETH Zürich, Switzerland. In 2002 he was undergraduate Marie-Curie Fellow at the Optoelectronics Research Center (ORC) of the TU Tampere, Finland. In 2003 he joined the MBE group at the Max-Planck-Institute for Solid State Research in Stuttgart, Germany, as PostDoc and became head of the "quantum dots" group in 2005. In 2007 he moved to the Leibniz Institute for Solid-State and Materials Research in Dresden, where he was staff member and head of Department until 2012. His research activities ranged from the epitaxial growth of III-V and group-IV semiconductor nanostructures to their structural, thermoelectric and optical properties and integration into optical microcavities. He is currently Professor and head of the Institute of Semiconductor and Solid Physics at the Johannes Kepler University in Linz, Austria. He is coauthor of about 170 articles and has given 60 invited talks and seminars. His current research focuses on the epitaxial growth of novel semiconductor nanostructures and manipulation of their electronic and optical properties after growth.

After the colloquium (around 16:00) we organize a mini-colloquium in which three COBRA researchers, one from each of the three COBRA groups, will give a short presentation about his or her work.

For the Photonics and Semiconductor Nanophysics Group:
Speaker: Döndü Sahin Title: Waveguide single-photon and photon-number-resolving detectors for quantum photonic integrated circuits
For the Electro Optical Communication Group:
Speaker: Wang Miao Title: Flat datacenter network architecture based on scalable and flow-controlled optical switching system
For the Photonic Integration Group:
Speaker: Valentina Moskalenko Title: Broadband Optical Coherent Frequency Comb from a Monolithic InGaAsP/InP Extended Cavity Ring Mode-Locked Laser

The audience is invited to an informal gathering following the colloquium (around 17:00) in the canteen of the Auditorium, section F!!! (see attachment)