Quantum Coherence Lab

Zumbühl Group


News from our Group

New on arXiv: Closed-form weak localization with arbitrary Rashba and Dresselhaus interactions

We derive a closed-form expression for the weak localization corrections to the magnetoconductivity of a 2D electron system with arbitrary Rashba and both linear and cubic Dresselhaus spin-orbit interactions in a perpendicular magnetic field geometry. In a reference frame with an in-plane z-axis along the spin-helix symmetry direction, we find a general decoupling algorithm for the Cooperon spin modes that leads to a representation invariant, closed-form expression. The anisotropy of the eff ective spin relaxation rates is fundamental to understanding spin-orbit coupling in quantum transport. Marinescu et al. arXiv:1811.04488

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New ArXiv submission: Effciently measuring a quantum device using machine learning

Tuning quantum devices is becoming time-consuming as systems are scaled up, e.g. to numerous gates or contacts, and will soon become intractable without automation. Here, we present measurements on a quantum dot done by a machine learning algorithm. This selects the most informative measurements to perform next using information theory and a probabilistic deep-generative model capable of generating multiple full-resolution reconstructions from scattered partial measurements. We demonstrate that the algorithm outperforms standard grid scan techniques, reducing the measurement time by a factor of ~4,  thus laying the foundation for automated control of large quantum circuits. Lennon et al., arxiv.org/abs/1810.10042

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"Ambipolar dots in Si finFETs..." published in Appl. Phys. Letters

Ambipolar quantum dots in silicon fin fi eld-eff ect transistors are defined using exclusively standard complementary metal-oxide-semiconductor fabrication techniques. We demonstrate stable quantum dot operation in the few charge carrier Coulomb blockade regime for both electrons and holes, opening the way for spin qubits hosted in such fin transistors. Appl. Phys. Lett. 113, 122107 (Sep 21, 2018).

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"Evolution of the Quantum Hall bulk spectrum" published in Nature Communications!

Using a GaAs cleaved-edge quantum wire, we perform spectroscopy revealing the momentum and position of the quantum Hall edge states with unprecedented precision. We present models in excellent agreement with the experiment—thus providing direct evidence for the bulk to edge correspondence. In addition, we observe Fermi level pinning, exchange-enhanced spin splitting and signatures of edge-state reconstruction. Published on Sept. 12 in Nature Communications, accompanied by an Uni News and a tweet.

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"Hyperfine-phonon spin relaxation" published in Nature Communications!

Understanding and control of the spin relaxation time T1 is a key challenge for spin qubits, setting the fundamental upper limit to the qubit coherence and readout fidelity. We establish the prediction of hyperfine-phonon spin relaxation experimentally, by measuring T1 over an unprecedented range of magnetic fields and report a maximum T1=57±15 s at the lowest fields, setting a new record for the spin lifetime in a nanostructure. Published on Aug 27 in Nature Communiations, with UniNews media release.

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