October 2026 - ITP-quantumseminare

Next week's QIT seminar
by Ladina Hausmann 15 Oct '26

15 Oct '26

Hi all, Next week Alessandro Palumbo will talk about “An Algebraic Approach to Quantum Reference Frames: Crossed Products, Edge Modes and Entropy Agreement”. See below for the abstract. The talk will take place on Monday at 15:30 in HIT E41.1. Best, Ladina %%%%%%%%%% Title: An Algebraic Approach to Quantum Reference Frames: Crossed Products, Edge Modes and Entropy Agreement Abstract: Recent works highlight the role of quantum reference frames (QRFs) in high-energy physics: they can account for the edge modes arising at the boundaries of a spacetime subregion and, under suitable assumptions, enable type reduction of local quantum field theory algebras via crossed product constructions. We generalise the QRF-based crossed product construction to locally compact symmetry groups and establish a classical counterpart for ideal frames. The classical construction clarifies the physical role of reorientations and allows us to identify a connection to the extra particle degree of freedom. Via a simple translational toy model we illustrate the relationships between different concepts appearing in the QRF literature: reorientations, the extra particle, edge modes and the Goldstone mode. Crossed product algebras can break the usual subsystem structure on which the trade-off between coherence and entanglement relies. Using an algebraic approach, we establish an entropy agreement theorem for ideal and non-ideal QRFs within the perspective neutral framework. This yields an algebraic entropy-defect trade-off that recovers the entanglement-coherence trade-off under its assumptions. The theorem extends the trade-off to settings involving different accessibility assumptions, crossed product algebras, and incomplete frames.

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Next week's QIT seminar
by Ladina Hausmann 07 Oct '26

07 Oct '26

Hi all, Next week, our visitor, Leon Loveridge, will talk about “Quantum Reference Frames, Locality, and Microcausality in Quantum Field Theory”. See below for the abstract. The talk will take place on Monday at 15:30 in HIT E41.1. Best, Ladina %%%%%%%%%% Title: Quantum Reference Frames, Locality, and Microcausality in Quantum Field Theory Abstract: In this talk, I'll introduce the operational framework for quantum reference frames, and give an overview of the main ideas and some recent results. I'll then discuss the example of translation-covariant quantum reference frames in Minkowski space, where the spectrum condition prohibits ideality of the frame. We will see that for a large class of frame states, strict locality is replaced by almost locality, and microcausality by commutators that decay rapidly with increasing separation, corresponding to an effective smearing of the light cone by the localisation density of the frame state. I'll also discuss measurement disturbance and causality in this setting. Finally I'll discuss the upshot that quantum field theories formulated relative to a quantum reference frame cannot rest on the traditional axioms, which must be updated by taking into account physically realistic properties of the frame.

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Next week's QIT seminar
by Ladina Hausmann 04 Oct '26

04 Oct '26

Hi all, Next Friday, our visitor Antoine (Choups) Soulas will talk about “A solution to the preferred-basis problem based on the WAY theorem”. See below for the abstract. The talk will take place on Friday at 14:00 in HIT E41.1. Best, Ladina %%%%%%%% Title: A solution to the preferred-basis problem based on the WAY theorem Abstract: The preferred-basis problem is an issue that arises in several fields of quantum foundations: decoherence theory (including its later developments like quantum Darwinism), consistent histories, the quantum-to-classical transition, as well as in some discussions about the measurement problem and the interpretation of QM. From a “3rd person perspective”, it can be formulated as follows: given the laws of physics, in which bases do systems preferably entangle and therefore mutually decohere? That is: about which observables does information accurately flow between systems? Equivalently, from a “1st person perspective”, it amounts to understand which measurements can actually be performed, while the vast majority of bases in the Hilbert space can not be probed in practice (e.g. Wigner’s unfeasible measurement on his friend). While a variety of models already exist, they remain arguably insufficient: lack of either universality or physical meaning, unrealistic Hamiltonians, circularity, diverging conclusions… In this talk, we propose a general solution to the preferred-basis problem which merely assumes the existence of a global symmetry, relying on the Wigner-Araki-Yanase (WAY) theorem and some basics of quantum reference frames. We further discuss the implications of this result for the quantum-to-classical transition.

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