Nanophysics and non-linear optics

Theoretical modelling of electron states and transport of electrons in low-dimensional nanodevices fabricated from semiconductor materials as e.g. GaAs/GaAlAs

Iryna Yakymenko, Karl-Fredrik Berggren and Ivan Yakimenko

Our current work deals with the study of effects of geometry and spin on magnetic focusing of electrons in semiconductor nanodevices, of electron interactions in formation of localized states and spin lattices. Experimental discovery of fractional quantum states in the absence of a magnetic field in the case of shallow confinement potential in a low electron density regime has pointed to the incipient formation of a Wigner crystal. Therefore, the project goal is to study the possibility of Wigner crystallization in quantum wire in the case of a weak confinement, explain the origin of fractional quantum states at zero magnetic field and to study the electron transport and conductance anomalies for experimental confinemen strength and electron densities. Further, we will consider possible application of fractional quantum states for quantum information processing and computing. Project is supported by Carl Trygger foundation for scientific research. It is based on a long term scientific interaction with Michael Pepper and Sanjeev Kumar at Nanotechnology Laboratory, Univeristy College UCL, London, concerning related experiments and interpretation.

Figure. Schematic view of a split-gate device containing one QPC made by rectangular split gates and a top gate.

Nonlinear dynamics of cubic and quadratic optical frequency comb

Tobias Hansson

Optical frequency combs are coherent sources of light with broad spectral bandwidth that are analogous to an optical ruler. Frequency combs have revolutionized precision measurements of frequencies and resulted in the 2005 Nobel Prize in physics. Applications of optical frequency combs are found within several areas such as spectroscopy, optical clocks and telecommunications. Our research aims to develop theoretical models and study the non-linear dynamics of a new type of microresonator based frequency combs with cubic and quadratic non-linearities. The project is financed by the Swedish Research Council.

Basic principle of quadratic comb generation through cascaded three-wave mixing processes. Illustration of frequency spectrum and energy level diagrams with pump, signal and idler frequencies. SHG – Second Harmonic Generation, OPO – Optical Parametric Oscillation, SFG – Sum Frequency Generation.