April 2017

Abstracts of the QSIT Lunch Seminar, Thursday, April 6, 2017

Electrostatically induced quantum point contact in bilayer graphene

Hiske Overweg - Nanophysics Group (Ensslin group), ETH Zurich

Bilayer graphene is a unique material for both fundamental physics and applications, because its band structure can be tuned by electrical gating. We show that it is possible to define a quantum point contact in bilayer graphene by locally inducing a band gap. The conductance of the quantum point contact shows quantized modes with a step size of 2 e2/h, whereas a step size of 4 e2/h would be expected for bilayer graphene. By fully pinching off the channel, we can reach a tunnel barrier resistance of 10 MΩ. Tunnel barriers with resistances of this order of magnitude are a promising step towards the realization of electrostatically defined quantum dots in bilayer graphene, which presumably have a long spin coherence time.

Electrically tunable artificial gauge potential for polaritons

Hyang-Tag Lim - Quantum Photonics group (Imamoglu group), ETH Zurich

Neutral particles subject to artificial gauge potentials can behave as charged particles in magnetic fields. This fascinating premise has led to demonstrations of one-way waveguides, topologically protected edge states and Landau levels for photons. In ultracold neutral atoms, effective gauge fields have allowed the emulation of matter under strong magnetic fields leading to realization of Harper-Hofstadter and Haldane models. Here we show that application of perpendicular electric and magnetic fields effects a tunable artificial gauge potential for two-dimensional microcavity exciton polaritons. For verification, we perform interferometric measurements of the associated phase accumulated during coherent polariton transport. Since the gauge potential originates from the magnetoelectric Stark effect, it can be realized for photons strongly coupled to excitations in any polarizable medium. Together with strong polariton–polariton interactions and engineered polariton lattices, artificial gauge fields could play a key role in investigation of non-equilibrium dynamics of strongly correlated photons.

 

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