Quantum Coherence Lab

Zumbühl Group

 
 

Welcome to the web page of the Quantum Coherence Lab

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.

 

Affiliations and Collaborations

 We are affiliated with

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

 

News from the Physics Department

Call for endress postdoctoral fellows in quantum science and quantum computing

The Center for Quantum Science and Quantum Computing (QSC) of the Universities of Basel (Switzerland) and Freiburg (Germany), embedded in EUCOR – The European Campus, invites applications for up to ten Georg H. Endress Postdoc Fellowships to start in 2018. The Center seeks to attract outstanding and highly motivated early-career scientists in QSC to engage in cutting-edge projects involving existing research groups at Basel and Freiburg. The ideal Endress Fellow has recently finished a PhD in experimental or theoretical physics (or related areas) and is eager to shape the academic environment in research and teaching at both nodes. Fellows will be appointed typically for up to three years, and will be selected on the basis of scientific excellence as well as quality and innovative potential of proposed research in the QSC target areas of the Center, such as quantum information processing (quantum computation, simulation, and metrology), quantum technologies, complex quantum systems, quantum materials, and other emerging topics in quantum science.

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Astronomy: A rotating system of satellite galaxies raises questions

Astronomers have examined the distribution and movement of dwarf galaxies in the constellation Centaurus, but their observations do not fit with the standard model of cosmology that assumes the existence of dark matter. The international team of researchers led by the University of Basel reported their findings in the journal Science.

 

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Optical nanoscope allows imaging of quantum dots

Physicists have developed a technique based on optical microscopy that can be used to create images of atoms on the nanoscale. In particular, the new method allows the imaging of quantum dots in a semiconductor chip. Together with colleagues from the University of Bochum, scientists from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute reported the findings in the journal Nature Photonics.

 

 

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Upcoming Events

28 Feb 10:15

1.09

Trial Talks March Meeting Part 1

28 Feb 14:15

3.12

Trial Talks March Meeting Part 2

2 Mär 13:15

1.09

Fabian

16 Mär 13:15

1.09

Mirko

 

News from the lab

Edge state tunneling spectroscopy paper on arXiv!

One of the most intriguing and fundamental properties of topological materials is the correspondence between the conducting edge states and the gapped bulk spectrum. So far, it has been impossible to access the full evolution of edge states in a magnetic field with critical system parameters due to poor resolution, remnant bulk conductivity, or disorder. Here, we present a novel type of tunneling spectroscopy which allows us to track the center of mass edge state positions with great precision and which can discriminate even spatially overlapping states due to their differing momenta based on tunneling along an extended GaAs quantum wire with translational symmetry. This results in unprecedented spatial resolution of about 1 nm at Tesla fields, while keeping the driving bias in the low microV regime in linear response.

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Master Project available

We are looking for a highly motivated master student who is interested in working on low temperature quantum transport experiments. The goal of those experiments is to utilize a new spectroscopy technique developed in our group with the aim to obtain the velocities of edge states in cleaved edge overgrown samples. For further information please refer to the following pdf document or contact Prof. Dr. Zumbühl and/or Taras Patlatiuk.

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Work on the European Microkelvin Platform (EMP) infrastructures proposal in Heidelberg

After hours of deliberations, changes and small-group work sessions, it's quite energizing to see the progress on the proposal achieved in the past three days in Heidelberg on the European Microkelvin Platform EMP!!

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Symmetry Breaking of the Persistent Spin Helix in Quantum Transport appeared on arXiv!

In this work, we show that the physics of the quantum corrections to the conductivity around the persistent spin helix symmetry point can be treated very similar to the case with weak spin-orbit (SO) coupling, where the small parameter is the deviation from the PSH point due to either the mismatch a-b of the Rashba a and Dresselhaus b linear terms or due to the cubic SO term b3. This similarity makes it possible to derive closed-form equation for the weak (anti)localization magnetoconductivity including all these SO terms, which turns out to be identical in form to the well-known Hikami-Larkin-Nagaoka expression, but is now reparametrized im terms of the small parameters a-b and b3. Further, we perform quantum transport experiments in the same PSH regime, and develop a reliable two-step method to extract all parameters from fits to the new expression, obtaining excellent agreement with other recent experiments. This provides experimental confirmation of the new theory, and helps advancing SO coupling towards a powerful resource in emerging quantum technologies.

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Coldest chip of the world went viral!!

Telebasel, Radio NRJ, Deutschlandfunk, Spiegel online, Newsweek, various Swiss, German and Austrian news papers, and even the Basel trams were featuring it, see picture... our low temperature record on a chip got a lot of attention!

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Group Dinner, Wednesday night, Dec 20, 2017

Really nice and fun group dinner last night, with some graduates coming back as well as a few select guests: great to see graduates Dorothee, Dario, Florian, and Tobias! And of course the two most recent doctors Mario and Pirmin! Great timing to have the "coldest chip of the world" appear on APL and UniNews on the same day! Great work: Christian, Mario and Dario and all coauthors! It was apparently all over Basel and the news media yesterday and today! Thanks also to all the group guests: Marta, Ilaria, Jelena, Floris and Daniel. Excellent meal, wonderful wine, and great atmosphere and, most of all, amazing speeches by everyone! Thanks very much for a wonderful evening! And a happy & successful new year!

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