April 2014
Abstracts of the QSIT Lunch Seminar, April 3, 2014
Atomic scale contacts to holes in SiGe quantum dots
Sigrun Koester, IBM Research - Zurich
When Ge is grown epitaxially on the Si(001) surface the 4% lattice mismatch leads to Stranski-Krastanov quantum dot growth on a Ge wetting layer. The type-II band alignment between Ge and Si leads to hole confinement in the dots. The spin of the valence band holes is of particular interest due to strong spin-orbit interaction which facilitates electric field tunability of the g-factor and heavy hole / light hole mixing. While larger dots, i.e. dome shaped islands, have already been studied experimentally, the smaller sized pyramids are not accessible by conventional lithographic techniques for transport measurements. Therefore, we aim to develop a method to contact such small dots with typical base lengths of around 10nm. Using hydrogen resist lithography done in a scanning tunneling microscope we can fabricate highly doped nanoscale leads aligned with atomic precision to the quantum dots. Macroscopic contacts then can be made by E-beam lithography. In this presentation I will give a brief review of the Ge growth and will then focus on the hydrogen resist lithography and doping for the nanoscale contacts. In this context first transport measurements on degenerately doped p-type delta-layers will be discussed.
Quantum limited amplification and entanglement of microwave fields with coupled nonlinear cavities
Christopher Eichler, Quantum Device Lab, ETH Zurich
Coupled nonlinear cavities provide a versatile testbed to study fundamental light-matter interactions and constitute a generic building block to realize photonic quantum simulators for strongly interacting systems. Their theoretical investigation and experimental realizations have therefore been driven forward in a variety of physical settings. In my talk I will present the implementation of a dissipative Bose-Hubbard dimer in superconducting circuits to achieve quantum limited amplification and to generate frequency entangled microwave photon pairs. Featuring a flexible control over the relevant system parameters, the presented lumped element circuit has also great potential to be used as an elementary cell in larger nonlinear cavity arrays. In contrast to previous implementations of microwave parametric amplifiers our device can be operated both as a bsingle mode squeezer and as a nondegenerate phase-preserving amplifier. In combination with its large achievable bandwidth, tunability and saturation power our device may find broad application in experiments aiming at quantum limited detection – particularly in superconducting circuits.
Collaborators: Y. Salathe, J. Mlynek, S. Schmidt, A. Wallraff