Talks and abstracts
Embezzling Entanglement From Relativistic Quantum Fields
Henrik Wilming, Leibniz Universität Hannover
Embezzlement of entanglement refers to the counterintuitive possibility of extracting entangled quantum states from a reference state of an auxiliary system via local quantum operations while hardly perturbing the latter. I will discuss a deep connection between the operational task of embezzling entanglement and the mathematical classification of von Neumann algebras. Our result implies that relativistic quantum fields are universal embezzlers: any entangled state of any dimension can be embezzled from them with arbitrary precision. This provides an operational characterization of the infinite amount of entanglement present in the vacuum state of relativistic quantum field theories.
Frame Dependence of Spekkens’ Contextuality for Relativistic Spin Systems
Ruben Campos Delgado, Leibniz Universität Hannover
In this talk I will discuss the notion of relativistic contextuality. In particular, I will show how the operational definition of contextuality introduced by Spekkens is, in general, frame-dependent. Indeed, while an observer in an inertial frame describes a contextual ontological model with respect to spin states and all possible spin measurements, an observer in a boosted frame can describe a non-contextual model with respect to the transformed spin states and all transformed spin measurements.
The talk is based on Phys.Rev.A 113 (2026) 1, 012202.
Quantum Photonic Networks With Semiconductor Quantum Dots
Michael Zopf, Leibniz Universität Hannover
Quantum dots are emerging as reliable, on-demand sources of single and entangled photons, compatible with wafer-scale fabrication and precisely tunable to interface with diverse quantum systems. These emitters can be integrated into compact photonic structures, generating high-quality photon streams that couple efficiently into optical fibers, enabling secure quantum key tribution across metropolitan distances. Together, these deterministic light sources, robust encoding methods, and hybrid photonic designs pave the way for scalable quantum photonic networks.
Real-time Lattice Approximations of Quantum Fields
Alexander Stottmeister, Leibniz Universität Hannover
Computer simulations are an indispensable tool to explore quantum field theories (QFTs) beyond the perturbative regime. It is common to base such numerical investigations on lattice discretizations of space (and time). Assuming that a given QFT is under sufficient control in a fixed discretization, we will discuss the problem of controlling the continuum limit. This is facilitated by treating QFTs arising in the scaling limit of near-critical models of (quantum) statistical mechanics as effective field theories. Following Wilson and Kadanoff, a QFT is understood as a coherent sequence of lattice models connected by the renormalization group, where each lattice model supplies the predictions appropriate for a certain energy scale (lattice spacing) together with a required precision – intuitively, the inverse lattice spacing should be at least double that of the features to be simulated to have reasonable error bounds following the Nyquist-Shannon theorem. This picture is mathematically implemented using operator-algebraic renormalization, a rigorous version of the Wilson-Kadanoff renormalization group in the Heisenberg picture. As a guiding example, we discuss the transverse-field Ising chain.
The Emergence of Spacetime From Quantum Mechanics
Leo Shaposhnik, Freie Universität Berlin
A fundamental question in the study of holographic dualities is how bulk gravity emerges from the quantum information structure of a holographic boundary theory. While the standard bulk/boundary dictionary allows one to relate local bulk operators to nonlocal boundary operators, a more microscopic understanding of the mechanism behind this relation remains hidden. One recent approach towards deepening our understanding of this relationship is concerned with the question of what properties of the boundary theory are sensitive to the bulk causal structure. This has led to the formulation of rigorous criteria by which one can judge, given any quantum-mechanical system, whether its dynamics are consistent with the dynamics of a semiclassical higher-dimensional bulk dual. This approach is based on an understanding of the bulk-to-boundary map as an encoding of quantum information in the form of subalgebra/subregion duality, where each subsystem of the boundary theory represents a particular piece of the emergent bulk and the algebraic structure of operators within it. This talk will introduce the basic methods and results that arose from these studies and the open problems that they raise.
Quantum Properties in High-energy Collider Experiments
Matthias Kleinmann, Universität Münster
Quantum entanglement has recently been observed in high-energy particle physics processes, exploring quantum information in relativistic regimes, but also posing conceptual and technical challenges in the interpretation of the results. In this talk, I will discuss the prospects of using concepts from quantum information theory to access quantum properties in collider experiments. Unlike in conventional quantum optics settings, the systems are relativistic and the particle momenta and measurements are not under active experimental control. Adapting methods from quantum information theory allows for enhanced ways to analyze quantum properties but also to test the soundness of the predictions from quantum field theory and the standard model in high-energy experiments. As a first proof of concept we illustrate the application of such methods to top pair production in the LHC using Monte Carlo simulations.
Existing Experiments Suffice to Indirectly Verify the Quantum Essence of Gravity
Martin Plávala, Leibniz Universität Hannover
The gravity-mediated entanglement experiments employ concepts from quantum information to argue that if entanglement due to gravitational interaction is observed, then gravity cannot be described by a classical system. However, the proposed experiments remain beyond our current technological capability, with optimistic projections placing the experiment outside of the short-term future. Here we argue that current matter-wave interferometers are sufficient to indirectly prove that gravitational interaction creates entanglement between two systems. Specifically, we prove that if we experimentally verify the Schrödinger equation for a single delocalized system interacting gravitationally with an external mass, then, under one of two reasonable assumptions, the time evolution of two delocalized systems will lead to gravity-mediated entanglement.
Atom Interferometers in Non-trivial Gravity:
Where Quantum Metrology Meets Einstein
Michael Werner, Leibniz Universität Hannover
Atom interferometers (AIFs) are highly accurate instruments used to measure inertial forces such as rotations and accelerations. They leverage the principles of quantum mechanics by coherently splitting the wave function of ultracold atoms (Rb, Yb, Cs, K,…) into a superposition of two momentum states, thereby creating a spatial superposition through the use of light pulses. By recombining the wave packets and measuring the resulting phase shift between the two momentum states, AIFs can accurately determine local gravitational accelerations or the imprinted photon recoil, among other phenomena. In Hannover, we have the "Very-Long-Baseline Atom Interferometer" (VLBAI), a 10-meter facility that represents the latest advancement in large-scale AIF experiments. It is the third of its kind globally, following similar setups in Stanford and Wuhan. AIFs not only allow measurement of the fine-structure constant with cutting-edge precision but also hold potential for detecting gravitational waves in the eagerly anticipated mid-frequency range and probing dark matter, especially if baseline lengths are extended to 100 - 1000 meters. To achieve these objectives, it is crucial to develop realistic and precise theoretical models to distinguish genuine signals from background noise. This presentation provides a comprehensive introduction to this field of research and explores key aspects that will play a pivotal role in the future.
Towards Measuring Tailored Gravity Fields Using the Very Long Baseline Atom Interferometer (Vlbai) Facility
Guillermo Alejandro Pérez Lobato, Leibniz Universität Hannover
One of the scientific objectives of the Very Long Baseline Atom Interferometry (VLBAI) facility in Hannover is to investigate how gravity affects quantum objects such as macroscopically delocallized atomic wave functions. Using the 10 m baseline we plan to position additional test masses at 15 cm from the atoms. Including and removing the additional test mass will allow us to perform a differential measurement in order to determine the gravitational influence of the test mass on the atomic wave function. For this measurement to be possible, a series of technical requirements have to be met. For example: launching an ultracold sample of atoms with sub-nanokelvin effective energies, and giving the atoms a differential momentum sufficient to macroscopically delocallize the wave function. This contribution focuses on the progress in the facility during the past year, including the prototype system for positioning the masses with mm accuracy, demonstrating atom interferometry, and the plans to achieve the full potential of the facility. These include the progress towards achieving highly delocallized matter waves by the manipulation of rubidium atoms utilizing purely optical potentials for matter wave lensing, and control of the kinematics of the atoms for manipulation with Bragg beam splitting processes and Bloch oscillations for launch.
