Selected Talks (Videos)

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

Further Recent Talks

  • 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
  • 03 Aug. 2023: QIQT 2023, Quantum theory from simple principles, spacetime, and 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.
  • 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. Slides
  • 06 Feb. 2023: Poster at QIP (Quantum Information Processing) ’23, Ghent, Testing quantum theory with generalized noncontextuality. Poster
  • 01 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”.
  • 09 Sept. 2022: DPG Meeting Regensburg, Testing quantum theory with generalized noncontextuality. Slides

Talks Before 2021

  • 6 Nov. 2021, Atominstitut, TU Vienna, Black boxes in space and time: semi-device-independent information processing via representation theory. Slides
  • 2 Nov. 2021, Habilitation Colloquium, University of Vienna, Quantum theory from simple principles. Slides
  • 15 Oct. 2021, Quantum Boundaries 2021 workshop, 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
  • 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
  • … To be completed.
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