Low temperature record published in APL as an Editor's pick, with Scilight!Image: A Coulomb blockade thermometer on a nuclear demagnetization stage.

Low temperature record published in APL as an Editor's pick, with Scilight!Image: A Coulomb blockade thermometer on a nuclear demagnetization stage.

Hyperfine-phonon spin relaxation paper appeared on arXiv, reporting spin lifetimes of up to one minute in a GaAs single electron quantum dot

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**Research** focuses on quantum transport experiments investigating quantum coherence, electron spins and nuclear spins and interactions in semiconductor and graphene nanostructures. Ongoing projects include

- spin qubits in coupled, laterally gated GaAs quantum dots
- microkelvin temperatures in nanoscale sample
- novel quantum states of matter, such as electron or nuclear spin helices, topological states and Majorana fermions
- spin-orbit coupling in GaAs quantum wells
- experiments investigating mesoscopic electron transport, including graphene nanoribbon research

We are interested in coherent manipulation of individual quantum systems in solid state nanostructures with quantum computation as a long term goal.

**Experiments** investigate quantum transport through semiconductor nanostructures which are fabricated in house using high mobility 2D electron gas materials obtained from collaborating molecular beam epitaxy labs. Experiments are typically performed in dilution refrigerators at millikelvin temperatures in magnetic fields. Measurements are done using electronic low-noise techniques and may involve nanosecond-pulsing and microsecond readout schemes.

An ERC Starting Grant from the first ERC call was awarded to our group and boosted our research from 2008-2013 (press release)

Positions are currently available, please see the positions page.

We are affiliated with

- Department of Physics, University of Basel
- Swiss Nanoscience Institute (SNI)
- Basel QC2 Center for Quantum Computing and Quantum Coherence
- Harvard Nanoscale Science and Engineering Center (NSEC) of the US National Science Foundation and
- NCCR Quantum Science and Technology - NCCR QSIT of the Swiss NSF. QSIT video

Our group enjoys numerous ongoing collaborations, including the following groups (in arbitrary order)

- Schönenberger group, Basel (nano-electronics, fabrication)
- Loss group, Basel (theory)
- Gossard group at UC Santa Barbara (MBE growth)
- Wegscheider group, ETH Zurich (MBE growth)
- Pfeiffer group, Princeton University (MBE growth)
- Yacoby group, Harvard University (GaAs quantum wires)
- Awschalom group, University of Chicago (persistent spin helix and spin-orbit coupling in GaAs quantum wells)
- Egues group, Sao Paulo University (theory)
- Pekola group, Aalto University, Helsinki (Coulomb blockade thermometry)
- Lancaster group (George Pickett), England (nuclear refrigeration)
- European microkelvin collaboration, ultra-low temperature physics and techniques (EU FP7 integrating activity)
- BaselCryogenics, Low temperature filtering and thermalization

At the 558th Dies Academicus, the Emilie Louise Frey-Preis 2018 is awarded to Katharina Laubscher for her Master thesis "Universal quantum computation using a hybrid quantum double model” carried out in the group of Prof. Daniel Loss.

Currently, Katharina is an Excellence Fellow of the PhD School “Quantum Computing and Quantum Technologies” and is doing her PhD in the group of Prof. Jelena Klinovaja in the field of topological quantum computing.

In her Master thesis, Katharina showed that it is possible to build novel planar quantum codes based on the combination of two different quantum double models, and that such hybrid codes constitute a novel pathway to universal fault-tolerant quantum computation. From a purely theoretical point of view, this is an important proof of principle and a large step towards a complete understanding of the quantum double models and their potential for quantum computation. From a more practical point of view, there may be direct advantages in terms of time- and special overhead of such a hybrid model compared to other techniques that enable universal fault-tolerant quantum computation, the most prominent one being a particularly resource-intensive procedure called magic state distillation.

Dr. Fabrizio Nichele received his doctorate in solid state physics from ETH Zurich in 2014. Since then he has been doing research at the University of Copenhagen and working as a consultant for Microsoft Research. Currently he is working at IBM Research Zurich. In 2018, the European Research Council awarded him an ERC Starting Grant. His project at the Department of Physics deals with fundamental physical questions and novel approaches to topological quantum states in lateral Josephson geometries.

Bell’s theorem has been proposed to certify quantum sources and measurements in a way that is independent of the imperfections of the actual implementation. The team of Prof. Sangouard showed how Bell’s theorem can be used to certify coherent operations for the storage, processing, and transfer of quantum information. This completes the set of tools needed to certify all building blocks of a quantum computer. These results have been published in Physical Review Letters and highlight by the SNF.

21 Dez 13:15

1.09

Group Meeting

4 Jan 13:15

1.09

Group Meeting

11 Jan 13:15

1.09

Florian

18 Jan 13:15

1.09

Mirko

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 effective spin relaxation rates is fundamental to understanding spin-orbit coupling in quantum transport. Marinescu et al. arXiv:1811.04488

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

Ambipolar quantum dots in silicon fin field-effect 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).

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.

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.

Published online on Aug 15 in Applied Physics Letters, our paper on gate defined quantum dots in Ge/Si nanowires, with single, double and triple dots, Pauli spin blockade, and signatures of a single hole quantum dot. Appl. Phys. Lett. 113, 073102 (2018).

**Research** focuses on quantum transport experiments investigating quantum coherence, electron spins and nuclear spins and interactions in semiconductor and graphene nanostructures. Ongoing projects include

- spin qubits in coupled, laterally gated GaAs quantum dots
- microkelvin temperatures in nanoscale sample
- novel quantum states of matter, such as electron or nuclear spin helices, topological states and Majorana fermions
- spin-orbit coupling in GaAs quantum wells
- experiments investigating mesoscopic electron transport, including graphene nanoribbon research

We are interested in coherent manipulation of individual quantum systems in solid state nanostructures with quantum computation as a long term goal.

**Experiments** investigate quantum transport through semiconductor nanostructures which are fabricated in house using high mobility 2D electron gas materials obtained from collaborating molecular beam epitaxy labs. Experiments are typically performed in dilution refrigerators at millikelvin temperatures in magnetic fields. Measurements are done using electronic low-noise techniques and may involve nanosecond-pulsing and microsecond readout schemes.

An ERC Starting Grant from the first ERC call was awarded to our group and boosted our research from 2008-2013 (press release)

Positions are currently available, please see the positions page.

We are affiliated with

- Department of Physics, University of Basel
- Swiss Nanoscience Institute (SNI)
- Basel QC2 Center for Quantum Computing and Quantum Coherence
- Harvard Nanoscale Science and Engineering Center (NSEC) of the US National Science Foundation and
- NCCR Quantum Science and Technology - NCCR QSIT of the Swiss NSF. QSIT video

Our group enjoys numerous ongoing collaborations, including the following groups (in arbitrary order)

- Schönenberger group, Basel (nano-electronics, fabrication)
- Loss group, Basel (theory)
- Gossard group at UC Santa Barbara (MBE growth)
- Wegscheider group, ETH Zurich (MBE growth)
- Pfeiffer group, Princeton University (MBE growth)
- Yacoby group, Harvard University (GaAs quantum wires)
- Awschalom group, University of Chicago (persistent spin helix and spin-orbit coupling in GaAs quantum wells)
- Egues group, Sao Paulo University (theory)
- Pekola group, Aalto University, Helsinki (Coulomb blockade thermometry)
- Lancaster group (George Pickett), England (nuclear refrigeration)
- European microkelvin collaboration, ultra-low temperature physics and techniques (EU FP7 integrating activity)
- BaselCryogenics, Low temperature filtering and thermalization

21 Dez 13:15

1.09

Group Meeting

4 Jan 13:15

1.09

Group Meeting

11 Jan 13:15

1.09

Florian

18 Jan 13:15

1.09

Mirko

At the 558th Dies Academicus, the Emilie Louise Frey-Preis 2018 is awarded to Katharina Laubscher for her Master thesis "Universal quantum computation using a hybrid quantum double model” carried out in the group of Prof. Daniel Loss.

Currently, Katharina is an Excellence Fellow of the PhD School “Quantum Computing and Quantum Technologies” and is doing her PhD in the group of Prof. Jelena Klinovaja in the field of topological quantum computing.

In her Master thesis, Katharina showed that it is possible to build novel planar quantum codes based on the combination of two different quantum double models, and that such hybrid codes constitute a novel pathway to universal fault-tolerant quantum computation. From a purely theoretical point of view, this is an important proof of principle and a large step towards a complete understanding of the quantum double models and their potential for quantum computation. From a more practical point of view, there may be direct advantages in terms of time- and special overhead of such a hybrid model compared to other techniques that enable universal fault-tolerant quantum computation, the most prominent one being a particularly resource-intensive procedure called magic state distillation.