Offer for the Research Phase (QST)

To assist you in finding topics for the research phase, a platform is available. The potential QST supervisors publish suitable topics with short descriptions that can be done in their group. The list thus provides an insight into possible topics for the final thesis in the Master's degree program in QST. If you are interested in a topic, please contact the research group. 

The list is not complete, so it is also worth asking the working groups directly. The exact titles and descriptions can of course be modified by the supervisor.

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
Prof. Dr. Stefan Filipp
Mentoring
Max Werninghaus M.Sc.
Description
The calibration and tune-up of superconducting qubits relies on the careful iteration of characterization measurements with increasing accuracy to understand the physical system and establish high-accuracy quantum-logical operations. For an extensive operation of large quantum chips, the tuneup protocol should be automated and set up with maximum efficiency to guarantee a high uptime of the quantum processor, and simultaneously minimize the bring-up time. In this project, you will implement a framework for automated and decision-based calibration graphs, and incorporate it into the software stack of the WMI. Physics-informed shortcuts will be implemented to make the traversal of the calibration graph as efficient as possible. As a comparison, the calibration framework will be compared against the linear and iterative tune-up routine. Finally, a WMI-built multi-dimensonal optimization algorithm should be incorporated as a shortcut in the graph to cover multiple calibration parameters, and compared against the performance of step-by-step tune-up routines.
Research Fields
Quantum Optics (Experiment) (50%)
Solid State Physics (Experiment) (50%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
Prof. Dr. Stefan Filipp
Mentoring
Federico Roy M.Sc.
Description
An iToffoli gate can be implemented for three qubits in a chain by selectively driving the 101-111 transition on the center qubit. This transition is made selective by realizing a ZZ (cross-Kerr) interaction between the qubits. Gate protocol is described in Baker et al. 2022 https://aip.scitation.org/doi/10.1063/5.0077443 and more generally in Rasmussen et al. 2020 https://journals.aps.org/pra/abstract/10.1103/physreva.101.022308. A very similar approach has been already implemented in Roy et al. 2020 https://journals.aps.org/prapplied/pdf/10.1103/physrevapplied.14.014072 and used to implement basic algorithms. In particular by using a separately programmable control line for each transition, they claim that generalized three-qubit controlled-phase gates can be implemented in software (claim to be verified). In this thesis, you will optimize the system and control pulses to achieve fast, high-fidelity gates while suppressing residual cphase-type interactions. A test sample will be designed, fabricated and measured to test findings in experiment.
Research Fields
Quantum Optics (Experiment) (50%)
Solid State Physics (Experiment) (50%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
PD Dr. Kirill Fedorov
Description
Entanglement is the phenomenon of composite quantum systems, where respective subsystems cannot be fully described independently of each other. Besides fundamental interest, quantum entanglement also represents a resource for many applications in the fields of quantum computing, quantum communication, and quantum sensing. However, entanglement is known to be a fragile entity, sensitive to unavoidable losses and external noise. Many strategies exist to remedy this problem. Here, the photon subtraction technique with entangled two-mode squeezed states [1] represents a novel experimental approach, relying on the application of single photon detectors. Such detectors can be implemented by parametrically driven superconducting qubits and nowadays are becoming available in state-of-the-art experiments. This master project focuses on the experimental optimization of existing microwave single photon detectors with transmon superconducting qubits and their application to propagating two-mode squeezed states generated with Josephson parametric amplifiers. Respectively, the project includes elements of quantum theory for simulation of dynamics of nonlinear superconducting circuits and cryogenic microwave measurements for benchmarking of the respective devices & entanglement distillation.
Research Fields
Quantum Optics (50%)
Solid State Physics (Experiment) (50%)

Research Group
Assistant Professorship of Quantum Networks (Prof. Reiserer)
Supervisor
Prof. Dr. Andreas Reiserer
Description
Erbium dopants in nanophotonic silicon resonators are a new hardware platform that has a unique potential for up-scaling of quantum computers using a modular architecture [for details, see e.g. https://www.nature.com/articles/s41467-024-55552-9 ]. To this end, it will be required to reduce the losses in nanophotonic waveguides and resonators that serve as spin-photon interfaces. In this M.Sc. thesis project, it will be studied if this can be achieved by pulsed laser annealing. This technique allows for controlled annealing that cures the crystal damage from erbium implantation. At the same time, it avoids excess diffusion of embedded photon emitters. If successful, this can lead to improved performance of nanophotonic devices that may constitute a promising step towards distributed quantum computers and global quantum networks. The student will learn about the design of nanophotonic components, their numerical evaluation, their measurement by laser spectroscopy and the design and operation of cryogenic measurement systems.
Research Fields
Festkörper und Materialphysik (50%)
Nanostructures (Experiment) (33%)
Quantum Optics (Experiment) (16%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
PD Dr. Kirill Fedorov
Description
Development of future quantum networks is an exciting research topic in modern science. Here, microwave quantum communication is set to play an important role because of its natural frequency compatibility with superconducting quantum processors and modern communication standards. Since cryogenic temperatures remain necessary for operation of superconducting circuits, we investigate potential approaches to alleviate technological costs of coherent communication between remote quantum nodes by relying on quantum teleportation through thermal channels operated at elevated temperatures. The goal of this thesis is to study temperature limitations of these communication channels for the quantum teleportation protocol, which involves potentially teleportation of qubit or single-photon states. This master project focuses on modelling of heat propagation in extended cryogenic systems development and experimental investigation of teleportation of various quantum states through thermal channels. The first part of this project includes elements of the condensed matter theory and quantum for modelling of optimal experimental parameters, while the second part focuses on microwave measurements of propagating quantum states and cryogenic techniques.
Research Fields
Quantum Optics (50%)
Solid State Physics (Experiment) (50%)

Research Group
Assistant Professorship of Quantum Networks (Prof. Reiserer)
Supervisor
Prof. Dr. Andreas Reiserer
Description
The implementation of global quantum networks is among the most intensely pursued research topics in quantum science and technology. Besides being of fundamental interest, such systems would also allow for numerous applications by connecting remote quantum computers and quantum sensors in order to enhance their capabilities. To implement such networks, one needs efficient hardware, in which stationary quantum bits are connected by optical photons, ideally in the "telecommunications window" where loss in optical fibers is minimal. We have recently established erbium-doped silicon nanophotonic resonators as a promising experimental platfrom that allows for the fabrication of quantum network nodes using established techniques of the semiconductor industry. However, to unleash this potential, a method to reliably tune many resonators on a single chip is an outstanding challenge. In this thesis, this will be developed by nanomechanical actuation. The student will learn about the design of nanophotonic components, their numerical evaluation, their measurement by laser spectroscopy and the design and operation of cryogenic measurement systems.
Research Fields
Quantum Optics (Experiment) (40%)
Nanostructures (Experiment) (40%)
Solid State Physics (Experiment) (20%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
PD Dr. Kirill Fedorov
Description
An Impedance-Matched Parametric Amplifier (IMPA) is a particular type of superconducting broadband microwave amplifiers which exploit parametric effects for quantum-limited amplification. These devices can be realized in a system of two coupled resonators which include nonlinear Josephson junctions. In order to prove the quantum-limited amplification of the IMPA, one has to perform characterization measurements based on the Planck spectroscopy, which exploits the black-body radiation law to accurately measure an added amplification noise. Overall, such devices represent a flexible device for many fundamental studies and applications, such as readout of superconducting qubits, generation of squeezed states, sources of entangled signals for quantum communication & sensing. This master project focuses on a design, fabrication, material optimization, and noise characterization of superconducting nonlinear circuits operated in the quantum regime. Particular tasks include electromagnetic simulation of thin-film structures realizing the IMPAs, their fabrication at WMI cleanroom facilities, and respective microwave measurements in a cryogenic environment.
Research Fields
Quantum Optics (33%)
Nanostructures (33%)
Solid State Physics (Experiment) (33%)

Research Group
Chair of Semiconductor Quantum Nanosystems (Prof. Finley)
Supervisor
Prof. Jonathan Finley Ph.D.
Mentoring
Adrian Otto Paulus M.Sc.
Description
We experimentally study the Fermi-Hubbard model in twisted 2D semiconductors, which host exciting Quantum Many-Body Phases. In this project we will spectroscopically study the rectangular moiré lattice formed by CrSBr, a magnetic 2D semiconductor, and thus go beyond the currently studied triangular moiré lattices. Over the course of your thesis, you will learn to work in state-of-the-art nanofabrication facilities and optical labs mentored and surrounded by diverse and ambitious scientists.
Research Fields
Optics (Experiment) (25%)
Quantum Optics (Experiment) (25%)
Festkörper und Materialphysik (25%)
Materials Physics (Experiment) (25%)

Research Group
Assistant Professorship of Quantum Networks (Prof. Reiserer)
Supervisor
Prof. Dr. Andreas Reiserer
Research Fields
Solid State Physics (Experiment) (100%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
PD Dr. Kirill Fedorov
Description
Microwave quantum communication is set to play an important role in future quantum networks because of its natural frequency compatibility with superconducting quantum processors and modern communication standards, such as 5G / 6G. Moreover, some of its protocols, such as quantum key distribution (QKD), provide the unconditional security of communicated data. Here, we would like rely on propagating quantum microwave signals generated with Josephson parametric devices and couple those to open-air channels, where thermal noise poses a substantial challenge. In order to correct for noise-induced errors in QKD, one has to apply error correction protocols which distil quantum correlations and extend the range of secure quantum communication. A particular type of the quantum error correction can be implemented using a single-photon subtraction operation, the application of which to the modern prepare-and-measure QKD protocols remains weakly studied and represents the main goal of the current project. This master project focuses on a theory simulation of quantum error correction protocols in its application to microwave QKD and a related experimental investigation using superconducting circuits. The project includes basics elements of quantum optics, microwave measurements, and cryogenic techniques.
Research Fields
Quantum Optics (50%)
Solid State Physics (Experiment) (50%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
Prof. Dr. Stefan Filipp
Mentoring
Dr. Benjamin Lienhard
Description
Currently, quantum processors with grids of qubits and interleaved couplers—comprising approximately 100 qubits—represent the forefront of quantum systems. To scale further, the design of qubit-coupler systems must be refined to minimize unwanted interactions beyond first-order and improve the overall operability and performance of both qubits and couplers. This thesis focuses on designing and simulating novel qubit-coupler architectures to enhance qubit performance, reduce crosstalk, and improve system operability, advancing the development of scalable and reliable superconducting quantum systems.
Research Fields
Quantum Optics (50%)
Nanostructures (50%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
Prof. Dr. Stefan Filipp
Mentoring
Dr. Klaus Liegener
Description
The standard-model of physics is a one of the most successful models of modern physics and uses the mathematical language of quantum field theory (QFT). Numerical calculations on it are often performed in the framework of lattice gauge theory. However due to the quantum nature of the theory, simulation on classical computers quickly turn out to be very challenging. The goal of the master thesis is to develop and eventually implement a digital quantum algorithm that simulates a lattice model of QFT. The algorithm will be developed with the experimental constraints of the superconducting quantum computing devices at the WMI in mind.The thesis can focus both on theoretical as well as on experimental efforts and is suited for students who are interested to get an introductory view of QFT and modern quantum computing. Algorithms: • VQE methods to develop shallow circuits and estimate running of the coupling for rough lattices • Coarse graining maps to develop a mapping of large lattices to small qubit devices
Research Fields
not assigned to a research field (50%)
Quantum Optics (Theory) (50%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
Prof. Dr. Stefan Filipp
Mentoring
David Bunch M.Sc.
Lasse Södergren Ph.D.
Description
Superconducting coplanar waveguide resonators are essential components in quantum circuits, used to readout or couple qubits, filter noise, or even act as qubits themselves. Two-level systems (TLS) contribute to energy loss in these resonators, affecting qubit performance and stability. This master's thesis project aims to characterize TLS properties in niobium (Nb) superconducting resonators and develop improved TLS loss models. The project involves fabricating Nb resonators and characterizing their quality factors (Q-factors) through temperature and power sweeps using frequency-domain analysis, and time-domain investigations to observe short-term resonator fluctuations arising from TLS dynamics. Advanced cryogenic setups and quantum-limited amplifiers (JPA or TWPA) will be utilized. Expected outcomes include precise characterization of TLS-related losses, reliable quantification of Q-factors, noise spectrum analysis, and the development of a superior TLS loss model that surpasses the standard tunneling model. These advancements could significantly enhance the performance and reliability of quantum circuits, paving the way for more stable and efficient quantum technologies.
Research Fields
Quantum Optics (Experiment) (50%)
Solid State Physics (Experiment) (50%)

Research Group
Chair of Technical Physics (Prof. Filipp)
Supervisor
Prof. Dr. Stefan Filipp
Mentoring
Gerhard Huber
Federico Roy M.Sc.
Description
The study of fermion-boson interactions is fundamental to varied phenomena in condensed-matter physics, including super-radiance, charge-density waves and high-temperature superconductivity. Particularly relevant are the regime of strong and ultra-strong couplings, which are however typically difficult to access in experimental devices. Recently, higher precision control of superconducting devices has enabled the simulation of coupled systems in a discrete, trotterized evolution of the interacting systems, enabling the digital recreation of these regimes with reasonable hardware parameters. This thesis aims to implement this trotterized evolution using superconducting qubits. First, you will design and simulate a superconducting qubit chip. You will then characterize and calibrate the fabricated design to then experimentally implement the evolution on the device. Along with internal supervision the project will take place in collaboration with theory experts to develop analytical models and simulations.
Research Fields
Quantum Optics (Experiment) (50%)
Solid State Physics (Experiment) (50%)

Research Group
Chair of Nanotechnology and Nanomaterials (Prof. Holleitner)
Supervisor
Prof. Dr. Alexander Holleitner
Mentoring
Prof. Dr. Eva Weig
Lukas Schleicher M.Sc.
Description
Do you want to fabricate atomistically thin, vibrating drums out of bulk crystals? During this MSc-project you will fabricate freely suspended van-der-Waals materials made from hexagonal Boron Nitride (hBN) and transition metal dichalcogenides (TMDC) and incorporate them into optical cavities. The resonators are interesting hybrid physical systems which allow for the mutual coupling of mechanical, electronic, as well as optical degrees of freedom. The electromechanical coupling is mediated by strain, and leads to a modification of the electronic bandstructure upon mechanical deflection, which allows for the coupling to excitons. The resonators are promising platforms in quantum technologies, e.g. for quantum sensing, single photon source, and generally, the transduction of various degrees of freedom. The project will be performed in a close collaboration between the physics department (Holleitner group) and the electrical engineering department (Weig group).
Research Fields
Nanostructures (Experiment) (100%)

Potential QST supervisors can manage their own offer of Research Phase topics via the application “Thesis” in the Digital School Services. They can find more information on thesis management in the NAT wiki.