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PHYSICS MATTERS: "Building small, fast and hot Si spin qubits" by Dominik Zumbühl

By Christine Marie-Therese Darve posted 13 days ago


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Quantum computers promise to execute complex tasks exponentially faster than any possible classical computer. Qubits based on hole spins in 1D Ge/Si nanowire are predicted to experience an exceptionally strong yet electrically tunable spin–orbit interaction. Here we used small gate voltage changes to tune the Rabi frequency and the driven coherence time by about a factor of 7, and its Landé g-factor by 50%. We can thus tune from a fast manipulation to an idle mode, demonstrating a spin–orbit switch. Finally, we used this control to optimize our qubit further and approach the strong driving regime, with spin-flipping times as short as ~1 ns.

 One of the greatest challenges in quantum computing is achieving scalability. Classical computing previously faced a scalability issue, solved with silicon chips hosting billions of fin field-effect transistors (FinFETs). Here, we show that silicon FinFETs can host spin qubits operating above 4 K, potentially allowing in-situ integration of qubit control electronics. We achieve fast electrical control of hole spins with driving frequencies up to 150 MHz, single-qubit gate fidelities at the fault-tolerance threshold, and a Rabi oscillation quality factor greater than 87. Our devices feature both industry compatibility and quality, and are fabricated in a flexible and agile way that should accelerate further development.

Biography: Dominik Zumbühl, University of Basel

After a physics diploma from ETH Zürich and a MSc at Stanford University, Dominik received his PhD at Harvard University in 2004, working on coherence and spin on GaAs quantum dots. After a brief postdoc at MIT, Dominik started his own group in 2006 at the University of Basel where he has been working since. In 2008, he received an ERC starting grant in the first ERC call. After being promoted to associate professor in 2012, he served as the Chair of the Department from 2015-2019. Since Feb 2021, he is the director of the NCCR SPIN, the Swiss National Program on Quantum Computing with Si and Ge spins. 

Dominik's research interests are in quantum transport experiments in semiconductor nanostructures, focusing on quantum computation with spins, coherence, interactions, quantum condensed matter at ultralow temperatures and machine learning for quantum devices.