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Semiconductor Nanostructures and Quantum Systems

Prof. Jonathan Finley

Research Field

Our group explores a wide range of topics related to the fundamental physics of nanostructured materials and their quantum-electronic and -photonic properties. We study the unique electronic, photonic and quantum properties of materials patterned over nanometer lengthscales and explore how sub-components can be integrated together to realise entirely new materials with emergent properties. This convergence of materials-nanotechnology, quantum electronics and photonics is strongly interdisciplinary, spanning topics across the physical sciences, as well as materials science and engineering.

Address/Contact

Am Coulombwall 4/I
85748 Garching b. München
+49 89 289 12771
Fax: +49 89 289 12704

Members of the Research Group

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Teaching

Course with Participations of Group Members

Titel und Modulzuordnung
ArtSWSDozent(en)Termine
Materials Science
Zuordnung zu Modulen:
VO 2 Finley, J. Fr, 10:00–12:00, PH HS3
Mi, 14:00–16:00, PH HS3
Übung zu Materialwissenschaften
Zuordnung zu Modulen:
UE 1
Leitung/Koordination: Finley, J.
Termine in Gruppen

Offers for Theses in the Group

Construction of a diamond magnetometer

Red fluorescent diamonds can serve as highly sensitive magnetic field sensors. Their operation is based on spectroscopy of a microwave transition in the Nitrogen-Vacancy (NV) color center - the defect causing diamonds to have a red color. Large diamonds doped with NV centers could provide magnetic field sensors with a sensitivity comparable to the best existing sensors, which are based on superconducting circuits ("SQUIDs"). They could enable measurements of currents in a human brain by accessing their tiny magnetic stray field.

We are looking for a person to construct such a device in our laboratory. Your work will consist in design of a benchtop-scale  setup for microwave and optical spectroscopy of millimeter-sized diamonds, as well as proof-of-principle measurements to benchmark the resulting sensitivity. 

suitable as
  • Bachelor’s Thesis Physics
Supervisor: Friedemann Reinhard
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
Supervisor: Jonathan Finley
Finite element simulation of nano-electromagnets

Our group is developing nuclear magnetic resonance imaging scanners, reminiscent of the MRI machines found in hospitals. In contrast to clinical machines our devices can access much smaller samples, down to single molecules. Imaging of these tiny objects requires strong magnetic field gradients, which we typically create by nano-fabricated conductors serving as electro-magnets. 

One important issue in these devices is heating and thermal expansion of the conductors, which degrades the quality of the MRI imaging. So far we have been relying on trial-and-error to assess the impact of this effect. 

Your task will be to put this research on a more solid foundation, by developing numerical models for current and thermal flows in nanoscale conductors. If things work out well, you might also be able to validate the results of your models by measurements on a real chip-scale MRI device. 

suitable as
  • Bachelor’s Thesis Physics
Supervisor: Friedemann Reinhard
Quantum Emitters in 2D Materials

2D materials were shown in 2015 to host randomly occurring single-photon emitting sites. Due to unique properties, such as ultimate proximity of the light sources to the surface that result in high photon extraction efficiencies, nuclear spin-free isotopes, valley pseudospin and potential for scalability, 2D materials are extremely promising as building blocks for solid-state photon-based quantum information. They have the potential to overcome the limitations of the current systems as highly sensitive, easily integrable quantum light sources and qubits of the future [1]. However, in current 2D quantum emitters the photon emission energy is random [2]. This prevents photon indistinguishability, a non-negotiable requirement for both fundamental studies and applications. Moreover, the current fabrication process is incompatible with silicon photonics and on-chip integration. To unleash the full impact of 2D materials on quantum science and technology, we are currently attempting a novel fabrication strategy. In the first part of the project, you will realize quantum dots of 2D semiconductors top-down, with dimensions below those achievable through conventional lithography systems, using a combination of etching masks made of colloidal quantum dots and by Helium Ion Beam Lithography followed by Reactive Ion Etching. Such quantum dots will be deterministic, scalable and will overcome the critical limitations of the current solid-state quantum emitters in 2D materials. You will study the optical properties of such quantum emitters at cryogenic temperatures and in the presence of magnetic fields. Further, you will have the option of integrating such quantum emitters and their arrays with optical cavities and waveguides, realizing spin-qubits registers made of arrays of independently charged quantum-dots and studying the effect of interactions among separate quantum emitters placed at a subwavelength distance. No current solid-state quantum dot system satisfies the requirements to do so. 

Some experience in the areas of optics, electronics, programming or cleanroom fabrication will be beneficial, but secondary to your personal motivation and commitment to this fascinating project. You will gain skills and knowledge and probably become an expert in various scientific research tasks, including but not limited to nanoscale cleanroom fabrication and state-of-the-art electro-optical measurements at cryogenic temperatures.

You should: be a highly motivated student with a curious and open mind looking to solve big problems. This is a challenging but potentially ground-breaking project in the framework of quantum science and technology. You will work in close collaboration with a small team of Ph.D. students and a postdoc, therefore teamwork is crucial. You must enjoy working with others, have a knack for a good laugh and you shouldn’t take yourself too seriously, these skills will help with the regular frustrations arising when doing research. 

You will get: experience on state-of-the-art (or beyond) nanofabrication and on performing optical spectroscopy in state-of-the-art laboratories, a sound understanding of the physics of 2D materials and solid-state quantum optical systems, and if everything goes well a nice (or even amazing) paper in a top journal. Maybe most importantly, you will also have a lot of fun along the way.

Finally, we like and promote a diverse working environment, as such we particularly welcome applications from female students, foreigners, and members of minority groups. 

For inquiries feel free to write to Dr. Matteo BarboneMatteo.Barbone@wsi.tum.de - or Marko Petric (marko.petric@wsi.tum.de) 


[1] Igor Aharonovich, Dirk Englund, and Milos Toth, Nat. Photon. 10 (10), 631 (2016)

[2] C. Palacios-Berraquero, et al., Nat. Commun. 8, 15093 (2017)

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Nuclear, Particle, and Astrophysics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Jonathan Finley
Quantum optics on coupled quantum dots

Solid-state qubits are a promising platform for future quantum technology applications. Among them, semiconductor-based quantum dot molecules (QDMs) - two coupled quantum dots – promise unique properties. Long coherence times (>1µs) and strong optical dipole transitions make them ideal candidates for quantum communication purposes.


Our group works towards the implementation of a multi qubit-photon interface by optically controlling spin states in QDMs.

In your Master's project, you will gain experience in nanofabrication while preparing QDM samples. However, the main part of your time you will spend in an optics lab: Besides studying the fundamental structure of QDMs, you will join in implementing resonance and pulsed excitation to the existing setup. This will enable the investigation and manipulation of charge spins in QDMs at cryogenic temperatures.

For successfully participating in the project, prior knowledge in optics and programming is beneficial. Being keen to learn about quantum optics and being able to work in a team is even more important.


If you are interested in joining the project and our group, please send your application (including CV and transcript of records) tofrederik.bopp@wsi.tum.de and finley@wsi.tum.de.

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Nuclear, Particle, and Astrophysics
  • Master’s Thesis Applied and Engineering Physics
  • Master’s Thesis Biomedical Engineering and Medical Physics
  • Master’s Thesis Matter to Life
Supervisor: Jonathan Finley
Searching for lasing in hexagonal SiGe nanowires

Fully merging thefields of integrated electronics and photonics is the major goal of distributed information processing today. However, a fundamental bottleneck is that cubic Si and Ge are both indirect bandgap semiconductors, which cannot emit light efficiently. Achieving efficient light emission from group-IV materials has been a holy grail in silicon technology for decades, but despite tremendous efforts, this has not been achieved.  Recently, the hexagonal crystal phase of Ge has been predicted to be a direct gap semiconductor, opening up a new route to achieving efficient light emitters on the basis of group IV semicodnuctors.  Growing hexagonal Ge and SiGe is non-trivial, but recently our collaboration partners have succeded.

In this thesis you will work as part of a team in close collaboration with several research groups from the Netherlands, U.K., Austria and Switzerland. You will perform spatially resolved optical spectroscopy on hex-Ge and SiGe nanowires to test the nature of their electronic bandstructure, increase the efficiency of their emission and, hopefully, demonstrate that they are indeed capable of emitting light efficiently.  You will learn about (near)infrared optics, cryogenics and contribute to this exciting research field.  You should be highly motivated, have ambition to work in a leading experimental physics group and sometimes willing to travel to consortium meetings to help discuss our results.


Interested ?  Contact Prof Finley or David Busse for more information on the thesis and to look around our laboratories.

suitable as
  • Master’s Thesis Condensed Matter Physics
  • Master’s Thesis Applied and Engineering Physics
Supervisor: Jonathan Finley

Current and Finished Theses in the Group

Cavity-enhanced field-resolved spectroscopy in the gas-phase
Abschlussarbeit im Masterstudiengang Physics (Applied and Engineering Physics)
Themensteller(in): Jonathan Finley
Construction of a nitrogen vacancy based quantum magnetometer
Abschlussarbeit im Masterstudiengang Physics (Applied and Engineering Physics)
Themensteller(in): Jonathan Finley
GaAs Quantum Dots as a Building Block for a Hybrid Semiconductor-Diamond Quantum Network
Abschlussarbeit im Masterstudiengang Physik (Physik der kondensierten Materie)
Themensteller(in): Jonathan Finley
Thermoelectric Properties of III-V Semiconductor Nanowires
Abschlussarbeit im Masterstudiengang Physics (Applied and Engineering Physics)
Themensteller(in): Gregor Koblmüller
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