## Selected Talks (Videos)

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QIQT 2023 (4th International Conference on Quantum Information and Quantum Technology, 9 May 2023): **Testing quantum theory by generalizing noncontextuality**

*It is a fundamental prediction of quantum theory that states of physical systems are described by complex vectors or density operators on a Hilbert space. However, many experiments admit effective descriptions in terms of other state spaces, such as classical probability distributions or quantum systems with superselection rules. Which probabilistic theories could reasonably be found as effective descriptions of physical systems if nature is fundamentally quantum? To answer this, we employ a generalized version of noncontextuality: processes that are statistically indistinguishable in an effective theory should not require explanation by multiple distinguishable processes in a more fundamental theory. From this, we propose an experimental test of quantum theory by probing single physical systems without assuming access to a tomographically complete set of procedures, arguably avoiding a significant loophole of earlier approaches.*

Algebra, Particles, and Quantum Theory seminar series, 23 May 2022:**Quantum theory and Jordan algebras from simple principles**

*Quantum theory is one of our most successful physical theories, but its standard textbook formulation is mysterious. For example, why are states described by complex vectors in a Hilbert space, and why do observables correspond to self-adjoint operators? In this talk, I describe how the Hilbert space formalism of quantum theory (and its Jordan-algebraic generalizations) can be reconstructed from simple physical or information-theoretic principles, without presupposing any of the usual mathematical machinery. This is conceptually similar to the derivation of the Lorentz transformations from the principles of relativity and the constancy of the speed of light. To this end, I introduce the framework of “generalized probabilistic theories” which generalizes both classical and quantum probability theory and which describes all possible consistent ways in which preparations and measurements can interact statistically in a laboratory. I give an explicit example of a set of principles that implies quantum theory, describe how the hunt for “higher-order interference” led to a scientific detective story, and show how these insights and techniques can shed surprising light on the relation between quantum theory and spacetime.*

Online seminar at OIST (Okinawa Institute of Science and Technology), 6 Feb. 2023: **Theory-independent randomness generation with spacetime symmetries**

*We characterize how the response of physical systems to spatial rotations constrains the probabilities of events that may be observed. From a foundational point of view, we show that the set of quantum correlations in our scenarios can be derived from rotational symmetry alone, without assuming quantum physics. This shows that important predictions of quantum theory can be derived from the structure of space, demonstrating that semi-device-independent scenarios can be utilized to shed light on the foundations of physics. From a practical perspective, these results allow us to introduce semi-device-independent protocols for the generation of secure random numbers based on the breaking of spatial symmetries. While experimental implementations will rely on quantum physics, the security analysis and the amount of extracted randomness is theory-independent and certified by the observed correlations only. That is, our protocols rely on a physically meaningful assumption: a bound on a theory-independent notion of spin.* Slides

“Nonlocal talks” online seminar (University of Campinas, Brazil), 25 Feb. 2021:**Physical Idealism**

*According to our current conception of physics, any valid physical theory is supposed to describe the objective evolution of a unique external world. However, this condition is challenged by quantum theory, which suggests that physical systems should not always be understood as having objective properties which are simply revealed by measurement. Furthermore, as argued below, several other conceptual puzzles in the foundations of physics and related fields point to limitations of our current perspective and motivate the exploration of an alternative: to start with the first-person (the observer) rather than the third-person perspective (the world).**In this work, I propose a rigorous approach of this kind on the basis of algorithmic information theory. It is based on a single postulate: that universal induction determines the chances of what any observer sees next. The resulting theory dissolves puzzles like cosmology’s Boltzmann brain problem, makes concrete predictions for thought experiments like the computer simulation of agents, and suggests novel phenomena such as “probabilistic zombies” governed by observer-dependent probabilistic chances.* Related paper in *Quantum*

## Recent Talks

**Boldface title **= invited talk.

- 14 March 2024, Billroth-Gymnasium Wien:
**Rätsel der Quantenwelt: lokaler Realismus, Quantenverschlüsselung und unser Universum**. - 10 Nov. 2023, RQI Circuit Vienna:
**How spacetime constrains the structure of quantum theory**. Video - 11 Sept. 2023, Rethinking the Foundations of Physics, LMU Munich:
**Testing quantum theory by generalizing noncontextuality**. Slides - 3 Aug. 2023, The Quantum Reconstructions Program and Beyond, University of Graz:
**Quantum theory from simple principles, spacetime, and what it tells us about interpretations**. Video - 9 July 2023, Foundations 2023, Bristol: Testing quantum theory by generalizing noncontextuality. Slides
- 2 June 2023, Physics Meets Philosophy workshop, Vienna:
**Information-theoretic idealism**. Slides - 24 May 2023, Borg3-Gymnasium Wien:
**Quantenphysik und der Satz von Bell***.* - 09 May 2023, 4th International Conference on Quantum Information and Quantum Technology (QIQT) 2023:
**Testing quantum theory by generalizing noncontextuality**. Video - April 2023, QISS (Quantum Information Structure of Spacetime) Spring School:
**It from qubit underground**. Slides, notes - 17 March 2023, QISS Virtual Seminar:
**How spacetime constrains the structure of quantum theory**. Video, slides - 6 Feb. 2023, Poster at QIP (Quantum Information Processing) ’23, Ghent: Testing quantum theory with generalized noncontextuality. Poster
- 6 Feb. 2023, Online seminar at OIST (Okinawa Institute of Science and Technology):
**Theory-independent randomness generation with spacetime symmetries**. Video - 1 Dec. 2022, Wigner’s Friends Theory Workshop, The Institute, San Francisco:
**Why we should study other observer puzzles together with Wigner’s friend**. - 17-18 Nov. 2022, Moderation of Essentia Foundation’s Online Conference 2022 “Quantum physics and the first-person perspective”.
- 9 Sept. 2022, DPG Meeting Regensburg, Hauptvortrag (“main lecture”):
**Testing quantum theory with generalized noncontextuality**. Slides - 23 May 2022, Algebra, Particles, and Quantum Theory seminar series:
**Quantum theory and Jordan algebras from simple principles**. Video

## Talks before 2022

- 2 Nov. 2021, Habilitation Colloquium, University of Vienna:
**Quantum theory from simple principles**. Slides - 15 Oct. 2021, Quantum Boundaries 2021 workshop, Nottingham, UK (online):
**Quantum theory from simple principles**. Video - 1 Sept. 2021, University of Ulm (online):
**Black boxes in space and time: semi-device-independent information processing via representation theory**. Slides - 11 June 2021, Atominstitut, TU Wien:
**Black boxes in space and time: semi-device-independent information processing via representation theory**. Slides - 1 June 2021, Banff International Research Station, Quantum Foundations, Gravity, and Causal Order (online):
**Quantum reference frame transformations as symmetries and the paradox of the third particle**. Video - 19 May 2021, USI Lugano (online):
**Computational irreducibility and notions of simulation for Turing machines**. Slides - 18 March 2021, APS March Meeting (online): Black boxes in spacetime: semi-device-independent information processing with spatiotemporal degrees of freedom.
- 25 Feb. 2021, “Nonlocal talks” seminar (online), University of Campinas, Brazil:
**Physical idealism**. Video - 15 Dec. 2020, Harvard Mini-Workshop on Probability and Undecidability (Harvard Foundations of Physics Series):
**From undecidability as undifferentiation to physics “without a world”**. Video - 8 Dec. 2020, Conference on Quantum Foundations, Technology and Applications (QFTA) 2020, Mohali, India (online):
**Black boxes in space and time:****semi-device-independent information processing****via representation theory**. - 26 Nov. 2020, Online NITheP Workshop on Quantum Thermodynamics:
**On the repeatable use of quantum resources in thermodynamics**. Video - 16 Nov. 2020, Essential Foundation Work Conference, Eindhoven:
**From enigmas of physics to a structural version of idealism**. Video - 9 Nov. 2020, Vienna Center for Quantum Science and Technology (VCQ) Colloquium talk:
**Black boxes in space and time: from quantum reconstructions to protocols**. Slides - 5 Oct. 2020, The Computing Community Consortium (CCC) Reversible Classical Computing Workshop (online):
**Reversible computing and the resource-theoretic approach to thermodynamics**. Slides - 22 Sept. 2020, Vienna Center for Quantum Science and Technology (VCQ) PI Day:
**Quantum Information Theory in the Foundations of Physics**. - 21 July 2020, ArtScience Monthly, STATE Studio Berlin:
**How are physics and math usually advertised, and what is my own motivation instead?**Slides - 5 Feb. 2020, 713. WE Heraeus-Seminar “Quantum Thermodynamics for Young Scientists”, Bad Honnef:
**Thermodynamics as a resource theory: versions of the second law(s)**. Slides - 3 Dec. 2019, Prize talk for Best Paper Award by ÖAW, Austrian Academy of Sciences Festive Hall:
**Der zweite Hauptsatz der Thermodynamik für einzelne Quantensysteme**. - 24 July 2019, Foundational Questions Institute (FQXi)’s 6th International Conference, Castelvecchio Pascoli, Italy:
**Mind before matter — why and how consider “idealist” worldviews?**Video - 3-10 July 2019, Les Houches School of Physics on “Quantum Information Machines”:
**Quantum Foundations and Probabilistic Theories**. Lecture Notes - 27 June 2019, Quantum ThermoDynamics Conference, Espoo, Finland:
**Thermodynamics as a resource theory: versions of the second law(s)**. Slides - 21 June 2019, Solstice of Foundations summer school, ETH Zurich:
**From observers to physics via information theory**. - 17 June 2019, Scientific Advisory Board Meeting, IQOQI Vienna:
**From correlation machines to spacetime boxes: a tour of informational physics**. - 1 June 2019, MCMP (Munich Center for Mathematical Philosophy)-Western Ontario Workshop on Computation in Scientific Theory and Practice:
**An approach in which the “first person” is fundamental and the external world is emergent**. - 23 May 2019, IQOQI Vienna Theory Breakfast:
**The second law in nanoscale thermodynamics****and no-broadcasting of reference frame information**. Slides - 29 March 2019, Physics-Philosophy Meeting, University of Vienna:
**Quantum theory as a principle theory: insights from information-theoretic reconstructions**. Slides - 13 March 2019, Subjectivist interpretations of quantum probabilities, École Normale Supérieure, Paris:
**QBism, beliefs, and the world: a reversal of perspective**. - 11 Dec. 2018, IQOQI Vienna Mini Workshop on the Foundations of Quantum Mechanics:
**Exact operational interpretation of entropy and free energy without the thermodynamic limit**. Slides - 10 Dec. 2018, Online Seminar “Mind-Matter Relation”:
**Law without law – from observer states to physics via algorithmic information theory**. Video - 19 Nov. 2018, IQOQI Vienna semester start lecture:
**Information in the foundations of (quantum) physics: an overview**. - 30 Sept. 2018, Workshop on Causation and Complexity in the Conscious Brain, Aegina, Greece:
**Could the first person perspective be a fundamental aspect of physics?** - 26 Sept. 2018, 2nd Workshop on Biological Mentality, Michigan State University, Ann Arbor, MI:
**From mental states to physics via algorithmic information theory**. - 20 Aug. 2018, Seminar talk at ETH Zürich, Renato Renner’s group:
**From observers to physics via algorithmic information theory**. Slides - 22 June 2018, Interdisciplinary workshop “Thermodynamics as a Resource Theory: Foundational and Philosophical Implications”, University of Western Ontario, Canada:
**Operational interpretation of entropy and free energy without the thermodynamic limit**. Video - 28 May 2018, Workshop “Interplay of Quantum Information, Foundations, and Gravity”, Vienna:
**Quantum theory and the structure of spacetime in the light of operationalism**. Video - 12 Dec. 2011, Poster at QIP (Quantum Information Processing) 2012, Université du Quebec à Montreal: Undecidability of Quantum measurement Occurrence. Poster
- 11 Jan 2011, Poster at QIP (Quantum Information Processing) 2011, Singapore: Concentration of measure for quantum states with a fixed expectation value. Poster
- 11-14 May 2010, Poster at A2 Meeting Reisensburg: Concentration of measure and the mean energy ensemble. Poster
- … To be completed.