Example topics (Master thesis)
From Classical to Quantum Non-Causality via the No-Cloning Theorem
Can the order of cause and effect be violated—and does it matter whether the world is classical or quantum? This project explores the boundary between classical and quantum non- causality using a rigorous mathematical framework for processes that defy ordinary causal order. It is motivated by a striking example in which a process that respects causality when restricted to classical operations becomes non-causal as soon as quantum operations are permitted. The goal is to understand this transition systematically and to determine whether it can always be traced back to one of quantum theory's most celebrated principles: the no-cloning theorem. More broadly, the project seeks to establish a deep connection between the impossibility of perfectly copying quantum information and the emergence of indefinite causal order.
- Guérin & Brukner, Observer-dependent locality of quantum events, doi:10.1088/1367-2630/aae742
- Dourdent et al, Paradox-free classical non-causality and unambiguous non-locality without entanglement are equivalent, arXiv:2512.23599
User-Friendly Shadow Tomography
How can we practically verify the state of a quantum device without an impractical number of measurements? Modern quantum technologies like quantum computers can manipulate finite-dimensional quantum systems with high coherence and fidelity. To analyze the performance and identify error sources, it is crucial to experimentally determine the quantum state of these devices. This is the task of quantum state tomography. The most recent theoretical advancement in this field is shadow tomography, which is a collection of techniques designed to enhance the efficiency and usability of quantum state reconstruction. However, these methods remain difficult to implement from both a mathematical and practical perspective. The aim of this project is to bridge the gap between theory and application, making shadow tomography more accessible and adapting it to meet realistic experimental requirements.
- Huang, Kueng & Preskill, Predicting many properties of a quantum system from very few measurements, doi:10.1038/s41567-020-0932-7
- de Gois & Kleinmann, User-friendly confidence regions for quantum state tomography, doi:10.1103/physreva.109.062417
Refined Bell Inequalities
Can we narrow down which assumptions behind a Bell inequality are violated by quantum mechanics? Quantum theory makes predictions that cannot be explained by local hidden variable models, that is, classical theories where observables have predetermined values and space-like separated experiments cannot influence one another. This fundamental difference can be verified through the violation of Bell inequalities. Recent progress shows that the assumptions underlying local hidden variable models can be decomposed into three distinct components: measurement independence, outcome independence, and parameter independence. Each of these can be relaxed while still allowing for a violation of a Bell-type inequality. The goal of this project is to improve these relaxations and minimize experimental requirements by finding stronger Bell inequalities.
- Vieira, Ramanathan & Cabello, Test of the physical significance of Bell non-locality, doi:10.1038/s41467-025-59247-7
Previous Theses
• Bachelor thesis of Salim Amin (2025): Testing quantum theory with mutli-slit interefernce
• Master thesis of Sebastian Schlösser (2024): Classical cost of simulating quantum measurements in the qubit case and beyond, arXiv:2603.01255
• Master thesis of Pascal Höhn (2022): State-independent contextuality with nonunit rank, arXiv:2207.11183
• Bachelor thesis of Fynn Otto (2021): Outcome irreducible measurements in generalize probabilistic theories
• Bachelor thesis of Michael Gaida (2020): Comparison of different notions of bound entanglement, arXiv:2212.11015
• Master thesis of Jonathan Steinberg (2019): Extensions and restriction of generalized probabilistic theories, arXiv:2105.09925
• Bachelor thesis of Jonathan Steinberg (2018): Structures in quaternionic quantum mechanics, arXiv:2001.05482
• Master thesis of Fabian Bernards (2018): Properties and generalisations of daemonic ergotropy, arXiv:1907.01970
• PhD thesis of Gabriel Fagundes (2018): Towards an experimental test of the quantum memory cost, arXiv:1902.06517, arXiv:1611.07515
• Master thesis of Núria Muñoz (2017): Operational differences between complex quantum theory and real quantum theory
• Master thesis of Christina Ritz (2014): Equivalence classes of entanglement in tripartite systems
• Diploma thesis of Jochen Szangolies (2012): Realistic error models for experimental tests of quantum contextuality, arXiv:1303.3837
• Bachelor thesis of Daniela Marzi (2008): Special relativity and quantum information theory