To celebrate the 100th anniversary of the "Umdeutung" paper, the UN declared 2025 the International Year of Quantum Science and Technology. For this reason, the theme of the annual meeting of the Basic Research Community for Physics (BRCP) will be A 100 years of quantum foundations: a retrospective of these 100 years of advances, paradoxes, and debates on the foundations of quantum mechanics.
https://brcp2025.sciencesconf.org/?lang=en
Invited Speakers:
- Dr. Gautier Depambour (CNRS)
Title of the presentation: "From the EPR thought experiment to Aspect’s experiments: how quantum optics contributed to settle the debate between Bohr and Einstein"
Abstract:
Almost all the experiments related to the foundations of quantum mechanics carried out in the 1970s-1980s were quantum optics experiments, since they relied on correlations between photon polarizations. However, the original debate between Albert Einstein and Niels Bohr over the interpretation of quantum formalism did not explicitly deal with the quantum nature of radiation.Likewise, the work of Irish physicist John Bell in the early 1960s, which reinvigorated this debate by demonstrating that it could be settled experimentally, remained highly abstract and did not directly involve the properties of light. In this talk, I will show how the epistemological debate between Bohr and Einstein gradually extended into the realm of experimental optics, especially thanks to Clauser, Horne, Shimony and Holt (CHSH) who proposed in 1969 an experimental scheme for testing Bell's inequalities in an optical experiment. Then I will present experiments testing the Bell-CHSH inequalities - thus addressing the foundations of quantum mechanics - such as those carried out by Aspect and his colleagues at Orsay in the 1980s.
- Pr. Alexei Grinbaum (CEA)
Title of the presentation: "Operationalism on the march: conceptual lessons of indefinite causality"
Abstract:
What did we learn after almost twenty years of research on indefinite causality? I submit that the main take-away is a clear understanding of the unbridgeable gap between the operational approach and physical theory in spacetime. Much like the device-independent models of nonlocality in previous decades, the models of noncausality teach us a quantifiable lesson about the fundamental concepts of systems and observers. If -- to celebrate the 100 years of Heisenberg's approach with a slightly refreshed formulation -- one wishes for a theory founded exclusively on inputs and outputs of physical experiments, then the space-time theoretical paradigm based on a geometric conception of events becomes an obstacle to further progress.
Contributed Talks:
- Maik Reddiger (Anhalt University of Applied Sciences)
Title of the presentation: "On the applicability of Kolmogorov's theory of probability to the description of quantum phenomena"
Abstract:
Through his axiomatization of quantum mechanics, von Neumann laid the foundations of a "quantum probability theory." In the literature this is commonly regarded as a non-commutative generalization of the "classical probability theory" established by Kolmogorov. Outside of quantum physics, however, Kolmogorov's axioms enjoy universal applicability. One may therefore ask whether quantum physics indeed requires such a generalization of our conception of probability or if von Neumann's axiomatization of quantum mechanics was contingent on the absence of a general theory of probability in the 1920s. Taking the latter view, I motivate an approach to the foundations of non-relativistic quantum theory that is based on Kolmogorov's axioms. It relies on the Born rule for particle position probability and employs Madelung's reformulation of the Schrödinger equation for the introduction of physically natural random variables. While an acceptable mathematical theory of Madelung's equations remains to be developed, one may nonetheless formulate a mathematically rigorous "hybrid theory", which is empirically almost equivalent to the quantum-mechanical Schrödinger theory. I provide an explicit example showing that the theory also makes predictions, which differ from the corresponding quantum mechanical theory. This talk is based on arXiv:2405.05710 [quant-ph] and Reddiger, Found. Phys. 47, 1317 (2017).
- Alexander Thomas (Université Claude Bernard Lyon 1)
Title of the presentation: "A new representation of (complex) numbers"
Abstract:
If you are asked how you represent a rational number, most people would say that it is a point on a line. In this talk, I'll show you some other ways of representing numbers using circles. This leads to amazing circle fractals which are highly symmetric.
- Adil Arsalan (UC Davis)
Title of the presentation: "A Search for Classical Subsystems in Quantum Worlds"
Abstract:
Decoherence and einselection have been effective in explaining several features of an emergent classical world from an underlying quantum theory. However, the theory assumes a particular factorization of the global Hilbert space into constituent system and environment subsystems, as well as specially constructed Hamiltonians. In this work, we take a systematic approach to discover, given a fixed Hamiltonian, (potentially) several factorizations (or tensor product structures) of a global Hilbert space that admit a quasi-classical description of subsystems in the sense that certain states (the "pointer states") are robust to entanglement. We show that every Hamiltonian admits a pointer basis in the factorization where the energy eigenvectors are separable. Furthermore, we implement an algorithm that allows us to discover a multitude of factorizations that admit pointer states and use it to explore these quasi-classical "realms" for both random and structured Hamiltonians. We also derive several analytical forms that the Hamiltonian may take in such factorizations, each with its unique set of features. Our approach has several implications: it enables us to derive the division into quasi-classical subsystems, demonstrates that decohering subsystems do not necessarily align with our classical notion of locality, and challenges ideas expressed by some authors that the propensity of a system to exhibit classical dynamics relies on minimizing the interaction between subsystems. From a quantum foundations perspective, these results lead to interesting ramifications for relative-state interpretations. From a quantum engineering perspective, these results may be useful in characterizing decoherence free subspaces and other passive error avoidance protocols.
arXiv: https://arxiv.org/abs/2403.10895