Research Phase and Master's Thesis in the Physics programs

The DEAP dark matter detector has been taking physics data for 3 years, searching for interactions between galactic dark matter particles and the argon target material. This unique dataset spanning hundreds of TB offers many opportunities to study liquid argon scintillation physics, optical processes, and background suppression techniques. MSc and BSc topics related to background suppression through pulse shape analysis, Dark Matter signal modelling, and the study of rare coincidences, are available. Students work within an international collaboration of over 100 physicists and might have the opportunity to visit the detector site at SNOLAB in Canada. Students will acquire skills in data analysis and statistics, C++ and/or python programming, Linux/Unix command line operation, Monte Carlo simulation, and in working with large datasets on high performance computing systems. Students have the chance to practice communicating physics results to other students and experts from many different institutions by presenting their work in bi-weekly project-wide analysis phone-conferences.

Bereits unsere eigene Existenz gibt einen Hinweis auf “neue Physik”. Die sichtbare Materie besteht aus Teilchen (nicht aus Antiteilchen), sodass während der Evolution des Universums zu einem bestimmten Zeitpunkt diese Asymmetrie zwischen Materie und Antimaterie durch einen bisher unbekannten Mechanismus hevorgerufen worden sein muss. Durch verschiedene experimentelle Daten können wir diese Asymmetrie sogar genau quantifizieren.

Die Emmy-Noether Gruppe “Baryogenese, Dunkle Materie und Neutrinos – Umfassende Analysen und präzise Methoden in der Teilchenkosmologie” unter der Leitung von Dr. Julia Harz befasst sich unter anderem mit der Fragestellung wie wir dem Mechanismus hinter der Baryonasymmetrie näher kommen können.

Im Rahmen dessen biete ich Masterarbeiten zu diesem Thema an:

(1) Eine mögliche Arbeit würde sich mit einem etabliertem, teilchentheoretischem Modell befassen, welches verschiedene offene Fragen (Dunkle Materie, Inflation, Baryogenese, Neutrinomassen etc.) addressiert. Dieses Modell soll mit einem sogenanntem globalen Fit in seinem Parameterbereich eingeschränkt werden. Das Projekt würde in internationaler Kollaboration stattfinden, während sich die Masterarbeit selbst auf den Bereich der Baryogenese fokusieren würde. Für diese Arbeit wären Programmierkenntnisse wünschenswert bzw. die Motivation solche selbständig zu erlernen.

(2) Eine zweite mögliche Arbeit würde sich mit der Möglichkeit beschäftigen, verschiedene Baryogenesemodelle mit Messungen am Large Hadron Collider zu testen. Für diese Arbeit wären fundierte, analytische Kenntnisse wünschenswert bzw. die Motivation sich mit ‘pen and paper’ in Rechnungen einzuarbeiten.

The CRESST (Cryogenic Rare-Event Search with Superconducting Thermometers) experiment operated at the Gran Sasso underground laboratory employs highly sensitive cryogenic detectors to the search for signals of the elusive dark matter particles, a main ingredient of the Universe whose nature is still unknown. 

The energy thresholds reached in CRESST-III are the lowest in the field, making CRESST the most sensitive experiment to light dark matter. Optimisation of the tungsten thin-film thermometers and of the techniques for data analysis promise still improvement in energy threshold, which could significantly boost the physics reach of the experiment.

Scientific topics

A student can contribute to:

- design, production and prototyping of new CRESST detectors in Munich 

- development of high purity crystals 

- development of new software tools for data analysis

- dark matter data analysis

and, if interested, can participate in the operation of the main experiment at Gran Sasso. 

Thesis can be carried out at the Max-Planck-Institute for Physics (MPP) und supervision of Dr. Federica Petricca (petricca@mpp.mpg.de) and/or at the Physics Department.

Chemische Prozesse an Oberflächen wollen verstanden werden. Wir verwenden modernste Methoden der magnetischen Resonanz, um solche Elementarprozesse zu beobachten, bei denen Spins eine Rolle spielen. Untersuchungsobjekte sind hochaktuelle oxidische Materialien für die Photokatalyse, die wir mit Hilfe von elektrisch und optisch detektierter magnetischer Resonanz studieren werden. Sie erlernen die Herstellung und Charaktersisierung dieser Materialien, das Arbeiten mit Kryostaten und Lasern, sowie die Grundlagen und Anwendungen der Elektronenspinresonanz.    

PERC (Proton Electron Radiation Channel) is a new neutron decay facility that is currently being constructed at the FRM II research reactor. PERC is a versatile source of decay electrons and protons and allows the measurement of several correlation coefficients of the neutron decay with an order of magnitude improvement in precision over current experiments. Measurements of these coefficients are a sensitive probe to investigate the mechanisms of the weak interaction.

The core component of PERC is an 8 m long superconducting magnet. Electrons and protons produced by neutrons decaying inside the magnet are guided along the magnetic field lines to the main detector system behind the spectrometer. Our group has previously used scintillator-based electron detectors for precision measurements of neutron decay correlations. Building on this experience, we plan to use similar devices to detect backscattering in PERC. The purpose of these backscattering detectors is to identify events where the decay electron only deposits a fraction of its energy in the main detector.

The objective of this thesis is the design and demonstration of the backscattering detectors for PERC, including the development of a new read-out system for electron spectroscopy with plastic scintillators and silicon photomultipliers (SiPMs).

Tasks

• Familiarize yourself with neutron decay studies and particle-tracking simulations.

• Optimize the design of the backscattering detectors for PERC based on simulation data.

• Develop and test a SiPM-based read-out system for plastic scintillators suitable for precision electron spectroscopy.

• Construct and test a prototype of the backscattering detectors.

What we offer

We offer you an interesting opportunity to participate in the development of a new high-profile experiment, allowing you to gain diverse experiences in the fields of detector physics, electronics, and low-energy particle physics!

Zur Verbesserung der Effizienz des Myontriggersystems des ATLAS-Detektors am Large Hadron Collider (LHC) werden neue schnelle Triggerdetektoren (Resistive Plate Chambers) gebaut, die sehr hohe Untergrundzaehlraten aushalten und hoehere Lebensdauer und Zeitaufloesung als bisher aufweisen. Die Eigenschaften dieser Detektoren werden in vorhandenen Testaufbauten und im Teststrahl am CERN systematisch untersucht.

Individual erbium spins in silicon and related materials show unique
promise for the realization of a global quantum network. To enable
single-spin control, the spins have to be integrated into optical
resonators of small size and high quality. Our group at the
Max-Planck-Institute of Quantum Optics (www.mpq.mpg.de/quantum-networks ) uses silicon nanophotonic structures to achieve this goal. While
individual resonators can be tuned by gas condensation, it is an
outstanding challenge to tune arrays of them into resonance both with
one another and with the Erbium spins. To achieve this goal, we will
analyze and implement several approaches based on nano-mechanics and
nano-electro-optics.

Physics: Nanophotonic structures, spins in semiconductors
Techniques: Nanofabrication, Nano-optics, laser-spectroscopy at
cryogenic temperatures.
Contact person: Andreas Reiserer (andreas.reiserer@mpq.mpg.de)

The smaller a device is, the higher its resonance frequency becomes. For our future quantum optomechanics experiments we will be working with mechanical resonators that operate at GHz frequencies and simultaneously couple strongly to light. Using mechanical and optical band structure calculations, you will design, make, and measure phononic and photonic cavities. The project involves nanofabrication in the cleanroom, as well as using the extreme sensitivity offered by on-chip optomechanics. We are aiming for devices made from silicon nitride, which has a lot of tensile stress in it. For micromechanical structures this material gives much better mechanical properties compared to, for example, silicon devices. An important aspect of the project is to understand if this is also true for the high frequency devices.

The computational design of new materials for heterogeneous catalysis relies on methods that can accurately predict adsorption energies of reactants and intermediates at low computational cost. Quantum-mechanical calculations based on the Density Functional Theory (DFT) are typically used for surface reactivity studies, but their cost significantly limits the number of compounds that can be evaluated as candidates for catalysing each targeted reaction. Scaling relations between adsorption energies of similar adsorbates and machine-learning approaches have been recently developed to circumvent this computational burden, but their application is currently limited to extended close-packed metal surfaces. Real catalysts are typically formed by supported metal nanoparticles exposing sites at different facets, edges, and corners. Dealing only with extended surfaces thus limits the predictive potential of computational catalyst design.

The goal of this M.Sc. project is to extend existing approaches for predicting adsorption energies to the description of undercoordinated sites typically found on metal nanoparticles. The candidate should be interested in electronic structure and machine learning methods, as well as in surface chemistry and catalysis. The student will learn how to perform DFT-based calculations and to use and asses the results of different machine learning methods. Basic knowledge of UNIX based operating systems and some experience with programming (and/or scripting) languages (preferably Python) is desirable, but not required.

Questions about the project can be directed to mie.andersen@ch.tum.de and albert.bruix@ch.tum.de. 

The microscopic foundations of magnetism and related phenomena are very active fields in current research. This is especially true for peculiar configurations such as highly anisotropic materials or magnetic frustration, where the onset of order is suppressed due to the competition of different types of coupling. Rare-earth tetraborides are realizations of such systems. Recently a strong magnetocaloric effect was found in TmB₄ [Orendáč et al., Sci. Rep. 8, 10933 (2018)] which indicates a strong relationship between magnetism and lattice. One can expect technical applications. It is the goal of this thesis to study the lattice excitations (phonons) in TmB₄ using inelastic light (Raman) scattering in an applied magnetic field at the onset of the different phases. The work includes a thorough introduction to spectroscopy, low-temperature, and high-field techniques. Contact: Andreas Baum, Rudi Hackl

Nano-mechanical beams are prototype harmonic oscillators, and can be straightforwardly integrated with other nanoscale systems. For example, coupling nano-beams to coplanar microwave cavities yields so-called hybrid electro-mechanical systems with intriguing properties, e.g., electro-mechanically induced transparency. In a similar fashion, ferromagnetic nanostructures can be integrated with nano-beams. This enables the design and the investigation of spin-phonon coupling down to the single excitation level, or nanoscale Einstein-de Haas experiments, in which the angular momentum change arising from magnetization reversal is transferred into a mechanical vibration of the beam. 

We are looking for a motivated master student for a magnetic nano-beam oriented master thesis. The goal of your project is to investigate the static and dynamic interplay between the mechanical properties of double layer nano-beams and its magnetic properties. In your thesis project you will fabricate freely suspended nanostructures based on silicon nitride and ferromagnetic multi layers using state-of-the-art nano-lithography and metal deposition techniques. Further, you will probe the mechanical response of the nano-structures using optical interferometry while exciting the magnetization dynamics of the magnetic system. 

In optomechanics, light is used to measure and alter the dynamics of mechanical resonators. It is by far the most sensitive method to observe the tiny vibrations that nanomechanical devices perform: in one second one can determine their position with femtometer precision! Using light to measure the mechanics is not the only aspect of optomechanics. The same light can also be used to change the dynamics of the mechanical device through a process called cavity backaction. The photons exert a force on the resonator, the so-called radiation pressure. In this project we want to explore the ultimate limits to this force. The goal is to measure the force originating from a single photon! For this it is required that the photon interacts with the mechanical resonator as strongly as possible. For this we need to the design and make very low loss optical cavities, such as microring resonators. Also, the mechanical device should have a quality factor as high as possible. You will make both the optical and mechanical components from chips with highly-stressed silicon nitride using state-of-the-art nanofabrication in the cleanroom. Then the devices are placed in a vacuum chamber for their measurement. In our highly-automated setup you can very quickly characterize many of the devices on your chip. Then, with the perfect device parameters you can start to explore the more advanced measurements. Initially we can measure the devices in with pulsed light, but by using single photons we want to explore the ultimate limits to optomechanical forces.

See http://www.groups.ph.tum.de/en/qtech/openings/ for a detailed description of this project.

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 Barbone: Matteo.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)

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.

In vielen wichtigen elektrochemischen Prozessen (wie zB der Reduktion von CO₂) vermutet man Prozesse, bei denen zwei Radikale beteiligt sind. Interessanterweise wurden diese chemischen Elementarprozesse noch nicht beobachtet. In dieser Arbeit soll eine elektrochemische Zelle in ein klassisches Spinresonanz-Spektrometer integriert werden und dann die Signatur solcher Biradikale im Stromtransport beobachtet werden. Sie werden in dieser Masterarbeit hochempfindliche Methoden der magnetischen Resonanz sowie die wichtigsten Askepte der Elektrochemie kennenlernen und an einem Thema an der vordersten Front der Physik und Chemie des Klimawandels forschen.   

Optomechanics provides extremely sensitive methods to measure the displacement of mechanical resonators. However, the forces are much smaller in optomechanics compared to those in nanoelectromechanical systems (NEMS). The goal of the project is to make, and measure opto-electromechanical devices which have strong electrostatic interactions. This includes the electrostatic spring effect where the resonance frequency depends strongly on the applied voltage. The next step is trying to measure the potential by measuring the ringdown of different mechanical modes. The devices will be made using advanced nanofabrication techniques such as electron beam lithography and reactive ion etching.

See http://www.groups.ph.tum.de/en/qtech/openings/ for a detailed description of this project.

Viele Erweiterungen des Standardmodells sagen neue schwere Resonanzen voraus, die in Bosonpaare, ZZ, WW, WZ, HZ, HW zerfallen. Mit Hilfe simulierter Daten werden die Selektionskriterien fuer diese Zerfaelle optimiert und die Nachweissignifikanzen bestimmt. Die Ergebnisse werden auf die neuesten Daten des ATLAS-Experiments bei der bisher hoechsten Proton-Proton-Kollisions- Energie von 13 TeV bestimmt.

Synchronization is a universal phenomenon that is knows since they days of Huygens. When two or more oscillators with slightly different frequencies are coupled, they will start to move in phase. We can create small mechanical devices using advanced nanofabrication techniques here on campus. By sending light of the right wavelength, they start to oscillate, and when increasing the power the optomechanical coupling synchronizes them. The goal of this project is to synchronize devices made from silicon nitride, which is a special material with a lot of stress in it, and to increase the number of synchronized oscillators. The larger the system becomes, the richer the nonlinear dynamics will become. You will first make the devices in the cleanroom, measure them, and analyze the data.

See http://www.groups.ph.tum.de/en/qtech/openings/ for a detailed description of this project.

Disorder has a drastic influence on transport properties. In the presence of a random potential, a system of electrons can become insulating; a phenomenon known as many-body localization (MBL) that has been envisioned by the Nobel laureate Phil Anderson. However, even beyond the vanishing transport such systems have very intriguing properties. For example, many-body localization describes an exotic state of matter, in which fundamental concepts of statistical mechanics break down. In this project we will explore these exciting aspects of many-body localization.