May 2025 - ITP-quantumseminare - lists.phys.ethz.ch

No QIT seminar this week
by Ladina Hausmann 26 May '25

26 May '25

Hi all, As Thursday is a holiday, there will be no QIT seminar this week. Best, Ladina

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This week's QIT seminar Thursday at 11:00 in HIT E 41.1
by Ladina Hausmann 20 May '25

20 May '25

Hi all, This week, Mischa Woods will tell us about why “Quantum theory does not need complex numbers”, see below for the abstract. The talk will take place on Thursday at 11:00 in HIT E41.1. Best, Ladina *** Title: Quantum theory does not need complex numbers Abstract: The longstanding debate over whether quantum theory fundamentally requires complex numbers--or if their use is merely a convenient choice--has persisted for decades. Until recently, this question was considered open. However, in [M.-O. Renou et al, Nature 600, 625-629, 2021], a decisive argument was presented asserting that quantum theory needs complex numbers. In this work, we demonstrate that a formulation of quantum theory based solely on real numbers is indeed possible while retaining key features such as theory-representation locality (i.e. local physical operations are represented by local changes to the states) and the positive semi-definiteness of its states and effects. We observe that the standard system combination rule--the tensor product--was derived after the development of single-system complex quantum theory. By starting from a single-system quantum theory using only real numbers, we derive a combination rule that produces a real quantum theory with properties analogous to those of conventional complex quantum theory. We also prove that the conventional tensor product rule can also lead to a real and representation-local theory, albeit with a modified characterization of the state space. We thus conclude that complex numbers are a mere convenience in quantum theory.

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This weeks QIT seminars
by Ladina Hausmann 13 May '25

13 May '25

Hi all, This week we will have two talks: (1) On Wednesday at 10:00 in HIT F11.1, our visitor Andrea Smirne will talk about “Multi-time statistics in open quantum systems: general definition and connection with non-classicality”. (2) On Thursday at 11:00 in HIT E41.1, Riccardo Cicchetti will talk about “Optimization Problems in Semi-Device-Independent Quantum Key Distribution Security Proof" See below for the abstracts. Best, Ladina *** Title: Optimization Problems in Semi-Device-Independent Quantum Key Distribution Security Proof Abstract: Quantum Key Distribution (QKD) is a well-established field of Quantum Information Theory with the promise of information theoretic secure key distribution protocols. Within this field, semi-Device Independent QKD address the challenge of providing the same security guarantee while giving no constraints on one party other than the laws of Quantum physics. In this master thesis, we walk step by step through a complete security proof, from the theoretical part to the numerical optimization. Although the results were inconclusive, the work highlighted challenges and area of development for the field. Title: Multi-time statistics in open quantum systems: general definition and connection with non-classicality Abstract: More than a century after the advent of quantum theory, the question of which properties and phenomena are genuinely quantum—meaning that they cannot be replicated by any classical theory—remains a subject of active investigation. In this talk, we will explore how and to what extent non-classicality can be rigorously associated with specific behaviors in the evolution of open quantum systems subjected to sequential measurements over time. We will first revisit the general framework for defining multi-time correlators in open quantum systems and consider the Kolmogorov consistency conditions as the characterizing feature of classical stochastic processes. We will then discuss some recent findings that relate the emergence of non-classicality to the dynamics of quantum coherences within the system, or to quantum correlations between the system and its environment, depending on whether the underlying process is Markovian or non-Markovian.

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No QIT seminar this week
by Ladina Hausmann 05 May '25

05 May '25

Hi all, There is no QIT seminar planned for this week. Best, Ladina

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