Quantum Coherence Lab

Zumbühl Group


News from our Group

On arXiv: Strong spin-orbit interaction and g-factor renormalization of Ge/Si nanowire hole spins

We report a remarkably strong spin-orbit interaction, with spin-orbit length of 65 nm, comparable to the quantum dot size. Combined with a large orbital effect of the B-field, the strong spin-orbit interaction causes a significant enhancement of the g-factor with magnetic field, as obtained from Pauli blockade spin mixing transitions (pic). This opens the door for ultrafast Rabi oscillations, efficient qubit-qubit interactions, as well as provide a new platform for Majorana zero modes. https://arxiv.org/abs/2007.04308


Pascal Würsch presents MSc Thesis

Pascal Würsch successfully completed his MSc thesis "Large Quantum Dots for Microkelvin Universal Coulomb Blockade Thermometry in Semiconductors" and presented his results to the group today on zoom. Formally, an ETH Zürich MSc thesis with advisor Prof. Klaus Ensslin, the research was done in our group in Basel. Congratulations, Pascal, and thanks very much for all the work!


PhD Defense of Florian Froning

Florian Froning successfully defended his PhD thesis "Hole Spin Qubits in Ge/Si Core/Shell Nanowires" on zoom, with Prof. Georgios Katsaros, Institute of Science and Technology, Vienna, Austria, and Prof. Menno Veldhorst, Delft University of Technology, Netherlands, as referees, and Prof. Daniel Loss as chair. Congratulations, Florian, on a great thesis, and thanks very much for all the work!


Fast Charge Readout with an Ultra-Low-Noise SQUID Amplifier: Published in Journal of Applied Physics!

Spin quantum computers will require fast and accurate qubit read out. Here, we use reflectometry with a SQUID preamplifier at 200 MHz to obtain record capacitance sensitivity of 0.07 aF/sqrt(Hz). Integrating for 1 μs, a signal-to-noise ratio of about 38 is obtained, allowing us to acquire a 100 x 100 pixel double-dot charge stability diagram in only 20 ms (see Figure). Schupp, Vigneau et al., Journal of Applied Physics 127, 244503 (Jun 29, 2020).


On arXiv: Ultrafast Hole Spin Qubit with Gate-Tunable Spin-Orbit Switch

We demonstrate an ultrafast qubit with Ge/Si core/shell hole spins, with spin-flipping times as short as ~1 ns - a new record for a single-spin qubit. Next, we show a large degree of electrical control over the Rabi frequency, Zeeman energy, and coherence time - thus implementing a spin-orbit switch toggling from a manipulation mode to an idling mode. The associated spin-orbit length that can be tuned over a large range down to 3 nm for holes of heavy-hole mass. https://arxiv.org/abs/2006.11175