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M.Sc. Christian Dangel

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Semiconductor Nanostructures and Quantum Systems

Offered Bachelor’s or Master’s Theses Topics

Electron Spin Qubits in Quantum Dot Molecules - Towards a Quantum Repeater


Quantum communication using single photons provides one route towards physically secure data transmission. However, the total length of today’s quantum key distribution systems is limited to about ~300km due to photon absorption in the “quantum channel” - typically an optical fiber. To overcome this problem, one can build so-called “quantum repeaters” in which the channel is broken down into shorter segments connected by quantum links. In our group we are working towards building a quantum repeater using optically active semiconductor-based quantum dot molecules.  We aim to make use of trapped pairs of charges – singlet-triplet (S-T) spin qubits.

In the first part of this MSc. project you fabricate a quantum photodiode structure containing coupled quantum dots. This will involve clean-room fabrication, as well as electrical characterization of the fabricated diodes. In the second part, your focus will be on optical characterization of the S-T spin qubits. The goal is to measure exceedingly long coherence times (>>1µs) for special electric fields where the energy gap of the qubit is insensitive to electric and magnetic field fluctuations.

Prior knowledge in optics, clean-room fabrication and programming are helpful – but secondary to high motivation and an open and curious mindset to tackle challenging problems. You will get experience in state-of-the-art nanofabrication, optical spectroscopy at cryogenic temperatures, as well as understanding of semiconductors in the context of quantum information and technology.

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
  • Master’s Thesis Biomedical Engineering and Medical Physics
  • Master’s Thesis Matter to Life
  • Master’s Thesis Quantum Science & Technology
  • Master’s Thesis Theoretical and Mathematical Physics
Supervisor: Jonathan Finley
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