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

Two TagesWoche articles on the research of the Physics Department

The Basler newspaper Tageswoche recently published two articles: one on Prof. Dr. Loss' supercomputer theory as well as an interview with astrophysicist Prof. emer. Dr. Thielemann on the fusion of neutron stars (available in German only).

Read more
 

Upcoming Events

19 Jan 13:15

1.09

Christian

26 Jan 13:15

1.09

Kris

 

News from the lab

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.

Read more

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!

Read more

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!

Read more

Low temperature record published in APL as an Editor's pick, with Scilight!

A Coulomb blockade thermometer was cooled to 2.8 mK with on-and-off chip magnetic refrigeration performed on a pulse tube dilution refrigerator platform... working towards new physics at ultralow temperatures. Published in Applied Physics Letters as an Editor's pick. See also UniNews, and featured in an AIP Scilight articlce!

Read more

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

Understanding and control of the spin relaxation time T1 is among the key challenges for spin based qubits. A larger T1 is generally favored, setting the fundamental upper limit to the qubit coherence and spin 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.

Read more