February 2011

Abstracts of the QSIT Lunch Seminar, February 3, 2011

Strong coupling regime in parabolic semiconductor quantum wells

Markus Geiser, Quantum Optoelectronics Group, ETH Zurich

Strong coupling in optical transitions between states in a modulation-doped parabolic potential well coupled to an inductance-capacitance microcavity is observed. A large Rabi frequency of 800GHz, corresponding to 20% of the electronic transition frequency, is found. The excitation frequency of the electron gas is independent of the electron density, verifying Kohn's theorem in the strong coupling regime. As a consequence, parabolic quantum wells are found to be ideal in order to obtain coupling energies comparable to the bare electronic transition frequencies, opening up the ultrastrong coupling regime.

Dynamical resurrection of the visibility in a Mach-Zehnder interferometer

Andrey Lebedev, Institut for Theoretical Physics, ETH Zurich

We study a single-electron pulse injected into the chiral edge-state of a Quantum Hall device and subject to a capacitive Coulombinteraction. We find that the scattered multi-particle state remains unentangled and hence can be created itself by a suitable classical voltage-pulse V(t). The application of the inverse pulse -V(-t) corrects for the shake-up due to the interaction and resurrects the original injected wave packet. We suggest an experiment with an asymmetric Mach-Zehnder interferometer where the application of such pulses manifests itself in an improved visibility.