June 2012

Abstracts of the QSIT Lunch Seminar, June 7, 2012

Observing the 5/2 Fractional Quantum Hall State – The Growth Side

Christian Reichl, Advanced Semiconductor Quantum Materials Group, ETH Zurich

Observing and performing experiments on extremely dilute Fractional Quantum Hall States (e.g. the most prominent one at a filling factor of 5/2) requires 2DEG structures of extraordinary quality. The epitactical growth of such high-performance structures has to be optimized in order to minimize the omni-present scattering mechanisms stemming from background impurities, interface roughness and donor-induced potential disorder. Here, an overview will be given how this optimization was done in the group of Werner Wegscheider with respect to electron mobility and prominence of Fractional Quantum Hall States. First measurements at low temperatures in the Millikelvin range are promising, but there are still several hot topics and a wide parameter space to be taken care of.

Probing charge noise in a semiconductor with laser spectroscopy on a quantum dot

Julien Houel, Nano-photonics group, University of Basel

Charge noise is a common, yet undesired, feature of semiconductor based devices. Charge noise is indeed responsible for spectral fluctuations observed in single quantum dot (QD) spectra, which prevents lifetime limited optical transitions to be achieved, an important feature for quantum information applications. Furthermore, it has been recently demonstrated experimentally that the hole spin dephasing time in a single InGaAs QD is likely to be limited by the charge noise. At this point, it is necessary to identify, quantify and suppress the electrical fluctuations at the QD location in semiconductor devices.

I will show that laser spectroscopy on a single InGaAs QD is a powerful single charge sensor, that enables us to probe, map and control the electrical mesoscopic environment of the QD. With this new understanding, we have designed new samples where the spectral fluctuations of the QD emission have been drastically reduced. Finally, using a resonance fluorescence detection setup, we have characterized the noise spectrum of the QD emission, under different excitation conditions, exhibiting different frequency behaviors.