May 2026 - ITP-quantumseminare - lists.phys.ethz.ch

Next week's QIT seminar
by Ladina Hausmann 29 May '26

29 May '26

Hi all, Next Friday, Lorenzo Biagi will talk about "A Game-Theoretic Approach to the Byzantine Generals Problem”. See below for the abstract. The talk will take place at 15:00 in HIT E41.1. Best, Ladina %%%%%%%%%%% Title: A Game-Theoretic Approach to the Byzantine Generals Problem Abstract: Can agreement be reached in a decentralized system corrupted by malicious agents? Modern distributed architectures rely on multi-party protocols that turn local, potentially inconsistent information into global reliable outcomes, even under failures or adversarial behaviour. Quantizing such protocols offers a direct way to probe quantum advantage by asking whether quantum resources can improve fault-tolerance thresholds. In this work, we pursue a game-theoretic route to quantizing Byzantine Agreement. We first introduce a formalism that recasts the Byzantine Generals Problem (BGP) as a finite-horizon dynamic Bayesian game. This lets us study decentralized agreement through game-theoretic solution concepts by encoding consensus in equilibrium strategies. Concretely, we establish an equivalence between Nash-Pareto equilibria and agreement-achieving protocols, which points to possible extensions of the classical solution space. This game-theoretic formulation opens a natural path to quantization. To this end, we propose an Eisert-type framework in which the BGP protocol itself generates the shared quantum resource, removing the reliance on a trusted arbiter and possibly improving traitor tolerance.

1 0

Fwd: Seminar Announcement: QFT and String Theory seminar / Quantum Information Theory seminar
by Renato Renner 28 May '26

28 May '26

Dear all The talk today at 14:00 (see below) may be of interest to those who are wondering what happens inside a black hole. Zhenbin is an expert on black holes and the paradoxes around them, so I can warmly recommend this talk. Best wishes Renato > Begin forwarded message: > > From: Beatrix Huber <beatrix.huber(a)itp.phys.ethz.ch> > Subject: Seminar Announcement: QFT and String Theory seminar / Quantum Information Theory seminar > Date: 26 May 2026 at 16:39:47 CEST > To: itp-all(a)lists.phys.ethz.ch > > Seminar Announcement > QFT and String Theory seminar / Quantum Information Theory seminar > > > Speaker: Zhenbin Yang (Tsinghua University) > > Location: HIT F 13 > > Date: Thursday, May 28, 2026 > > Time: 14.00 h > > Title: Chaotic properties of de Sitter horizon > > Abstract: > > The introduction of an observer in de Sitter space introduces the notion of an energy and closed system. I will discuss some properties of this closed system from a conjectured holographic perspective, and some related puzzles. > > > sig. M. Gaberdiel

1 0

No QIT seminar next week
by Ladina Hausmann 21 May '26

21 May '26

Hi all, Due to the holiday on Monday, there is no QIT seminar next week Best, Ladina

1 0

Monday's QIT seminar at 16:45
by Ladina Hausmann 14 May '26

14 May '26

Hi all, Next Monday we will have two seminars: (1) Heiko Schwab will tell us about “Quantum Resource Trade-offs in Quantum Reference Frames on the Lattice” (2) Lucas Hörl will tell us about “Quantum extremal surfaces and the black hole information problem” See below for the abstracts. The talks will take place on Monday at 16:45 in HIT K52. Best, Ladina %%%%%%% Title: Quantum Resource Trade-offs in Quantum Reference Frames on the Lattice Abstract: The study of quantum reference frames (QRFs) and their transformations has demonstrated the relational nature of entanglement and coherence. Motivated by the central role these quantum resources play in quantum information processing, it was recently shown that the sum of particular quantifiers of these resources remains invariant under ideal QRF transformations. A first step in generalizing this result from the quantum information- to the field-theoretic setting is to consider quantum reference frames on a spatial lattice. Inspired by the Hamiltonian formulation of lattice gauge theory, we propose a possible extension of the perspective-neutral formulation of QRFs to the lattice by explicitly considering a Z_2 gauge theory and analyze the entanglement-coherence trade-off for QRFs on the lattice in this concrete case. This leads us to propose a quantum resource trade-off for transformations between ideal and non-ideal QRFs on the lattice in terms of a generalized invariant with an operational meaning as a relative entropy. %%%%%%%%% Title: Quantum extremal surfaces and the black hole information problem Abstract: This talk reviews the quantum extremal surface prescription and its role in the black hole information problem. Starting from the Bekenstein-Hawking entropy, I introduce holographic entanglement entropy, the Ryu-Takayanagi formula, and its quantum generalization leading to the island rule. I then discuss the information problem in a concrete toy model, namely two-dimensional JT gravity coupled to a non-gravitating bath. In this setting, the replica trick, including the contributions from replica wormhole saddles, gives a controlled derivation of the Page curve for Hawking radiation. I conclude with a brief overview of my semester project, which studies corrections to this semiclassical picture, and makes steps towards understanding the radiation of black holes prepared in superpositions of semiclassical geometries and one-loop corrections to JT gravity coupled to a bath.

1 0

Monday's QIT seminar
by Ladina Hausmann 08 May '26

08 May '26

Hi all, On Monday, Apostolos Giovanakis will talk about “What is accessible from the perspective of a non-ideal QRF?”. See below for the abstract. The talk will take place on Monday at 15:00 in HIT K52. Best, Ladina %%%%%%%%%% Title: What is accessible from the perspective of a non-ideal QRF? Abstract: A central question in the study of quantum information theory in the presence of symmetries concerns which properties of a system can be inferred by observers without access to the laboratory frame. We investigate this question by introducing the relational observables described from the perspective of a quantum reference frame (QRF). However, non-ideal (spatial) QRFs have finite resources and cannot keep track of position perfectly. This might suggest that they are operationally less useful than reference frames with infinite resources that are often considered. In this talk, I will explore whether the opposite is possible: are there any features that arise in the non-ideal case that are absent in the ideal one, thereby rendering non-ideal QRFs more advantageous? More generally, I will discuss how an observer can operationally describe and access observables relative to a non-ideal QRF.

1 0