June 2015

Abstracts of the QSIT Lunch Seminar, Thursday, June 4, 2015

Stabilized skyrmion phase detected in MnSi nanowires by dynamic cantilever magnetometry

Andrea Mehlin, Poggio Lab, University of Basel

Using dynamic cantilever magnetometry we measure an enhanced skyrmion lattice phase extending from around 29 K down to at least 0.4 K in single MnSi nanowires (NWs). Although recent experiments on two-dimensional thin films show that reduced dimensionality stabilizes the skyrmion phase, our results are surprising given that the NW dimensions are much larger than the skyrmion lattice constant. Furthermore, the stability of the phase depends on the orientation of the NWs with respect to the applied magnetic field, suggesting that an effective magnetic anisotropy - likely due to the large surface-to-volume ratio of these nanostructures - is responsible for the stabilization.  The compatibility of our technique with nanometer-scale samples paves the way for future studies on the effect of confinement and surfaces on magnetic skyrmions.

Fast coherent state generation through bang-bang control of a trapped ion

Florian Leupold, Trapped Ion Quantum Information, ETH Zurich

Methods for controlling quantum states of matter are of primary interest for quantum computing, simulation and metrology. Control operations on trapped-ion oscillator states primarily make use of resonant effects or adiabatic control, which are in both cases limited to long timescales compared to the natural frequency of the oscillator and make such control susceptible to noise. I will describe a new setup in which we realize bang-bang control of a trapped ion oscillator using switching of the trapping potentials on nano-second timescales, much faster than the ion can respond. Technically this involves a novel step of placing CMOS electronics in our cryogenic vacuum system close to the trap itself. In a first exploration of this technology, we have demonstrated control of coherent states with up to 10,000 quanta of energy and have used these displaced states to verify the Franck-Condon factors for the light-atom interaction far outside the usual regime for trapped-ion work. I will outline how bang-bang control might be used to speed up transport in ion trap quantum processing by more than an order of magnitude, as well as other opportunities for quantum state engineering.