University of Basel

Department
of Physics

Quantum Coherence Lab - Zumbühl Group

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On arXiv: Reducing the hydrogen content in liquid helium

Molecular hydrogen can block liquid He (LHe) intake capillaries typically used on 1K pots of many cryostats, causing severe disruption to the experiments. Here, we measure molecular hydrogen content in the liquifier helium gas supply and…
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On arXiv: Isotropic and Anisotropic g-factor Corrections in GaAs Quantum Dots

The spin splitting defines the qubit energy and is one of the fundamental properties of a semiconductor electron in a magnetic field. Here, we measure and separate the isotropic and anisotropic corrections to the bulk g-factor in two GaAs…
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On arXiv: Quantum measurement induced a many-body transition

The act of measurement in quantum mechanics is still mysterious and not microscopically understood. In our work, we show that even a weak (non-projective) measurement of a quantum dot system with an adjacent detector can result in a…
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On arXiv: Deep Reinforcement Learning for Efficient Measurement of Quantum Devices

Deep reinforcement learning is an emerging machine learning approach which can teach a computer to learn from actions and rewards similar to the way humans learn from experience. Here, we use this approach for fully automatic identification…
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Published in New Journal of Physics: Fine-tuning with unsuperv. embedding learning

We demonstrate an algorithm capable of fi ne-tuning several device parameters at once. The algorithm acquires a measurement, scores it using a variational auto-encoder, and optimizes gate voltage via the score in real-time in an…
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Group Hike to Wissigstock 2'887m

Shot of the brave thirteen who took it upon themselves to hike all the way to the top of Wissigstock at 2'887 meters altitude... refreshed and slightly proud... enjoying the breathtaking view from up there!
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/ Research

New SNI PhD School Project Approved with Floris Braakman and Martino Poggio

The SNI has approved the PhD student project "Scanning Nanowire Quantum Dot" lead by Dr. Floris Braakman, to be carried out in the Poggio and Zumbühl labs, starting in 2021. Congratulations, Floris!
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Spin stability record makes the morning radio show!

This morning Dominik tries to explain the 57 seconds spin stability record from Leon and Liqui's experiment to the audience of local radio Basilisk... with Austin Powers background music and a totally baffeled radio show host! listen in... …
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Published in Phys. Rev. Lett.: Edge-State Wave Functions from Momentum-Conserving Tunneling Spectroscopy

We employ the lowest 5 modes of a quantum wire to probe adjacent edge-states in momentum conserving tunneling spectroscopy. Combined with numerical Schrödinger-Poisson simulations this is a powerful technique to probe edge-state wave…
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Fully automatic tuning of a quantum device faster than human experts, Nature Comms

Robots taking over the quantum transport lab: In an up to 8D space, our machine learning algorithm tunes the device typically in under 70 minutes, surpassing our best human benchmark (although both human and machine performance can be…
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On arXiv: Silicon quantum dot devices with a self-aligned 2nd gate layer

We present silicon finFET quantum dots with perfectly self-aligned 2nd gate layer and gate lengths down to 15 nm. In a double quantum dot, we find Pauli spin blockade with leakage dominated by spin-orbit interaction and extract a hole…
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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…
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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…
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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…
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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…
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