This thread will collect detailed information about past seminars, including links to the video recording and the presentation slides when available.
Date and time: 16 April 2026, 15:00 (CEST)
Speaker: Jonathan Oppenheim (University College London)
Title: Decoherence vs diffusion: testing the quantum nature of gravity
Abstract: We consider two interacting systems when one is treated classically while the other remains quantum. The most general form of such dynamics can be derived and has implications for the foundations of quantum theory, and for the problem of understanding gravity when spacetime is treated as fundamentally or effectively classically. In particular, we construct a consistent classical-quantum description of general relativity coupled to quantum field theory. The pure gravity theory is formally renormalisable. If any system is treated as fundamentally classical, the dynamics necessarily results in decoherence of quantum systems, and a breakdown in predictability in classical phase space. Nonetheless the quantum state remains pure conditioned on the classical trajectory. We prove that a trade-off between the rate of decoherence and the degree of diffusion induced in the classical system is a general feature of all classical-quantum dynamics. Applying the trade-off to general relativity enables us to experimentally test the nature of spacetime. Bounds on decoherence rates arising from interferometry experiments, combined with precision acceleration measurements, squeezes the theory from both sides and can be used to rule out theories in which spacetime is described classically.
Video recording: https://youtu.be/lvd60KjTH0g
Presentation slides: https://drive.google.com/file/d/1bQysFpH7_4QeCDcFYjxBYNp0pTKkBaXz/view?usp=sharing
Date and time: 21 May 2026, 15:00 (CEST)
Speaker: Maria Chiara Braidotti (University of Glasgow)
Title: Exploiting Rotation for the Generation of Quantum Entanglement
Abstract: Rotation, a fundamental form of non-inertial motion, can profoundly influence the behaviour of quantum systems. In this presentation, I will discuss recent advances in understanding how rotational motion affects quantum correlations and entanglement. Building on a novel approach that combines Sagnac interferometry with modern quantum techniques, I will show how rotation can expose, modify, and even generate entanglement between particles that are initially uncorrelated. These results open new perspectives on the interplay between motion and quantum information, while laying the groundwork for future applications in quantum sensing and relativistic quantum technologies.
Date and time: 18 June 2026, 10:00 (CEST)
Speaker: Torsten Zache (Universität Innsbruck)
Title: Non-local mass superpositions and optical clock interferometry in atomic ensemble quantum networks
Abstract: Quantum networks are emerging as powerful platforms for sensing, communication, and fundamental tests of physics. We propose a programmable quantum sensing network based on entangled atomic ensembles, where optical clock qubits realize mass superpositions arising via mass-energy equivalence, as in atom and atom-clock interferometry. Our approach uniquely combines scalability to large atom numbers with minimal control requirements, relying only on collective addressing of internal atomic states. This enables the creation of both non-local and local superpositions with spatial separations beyond those achievable in conventional matter-wave interferometry with single atoms. Starting from Bell-type seed states distributed via photonic channels, collective operations within atomic ensembles coherently build many-body mass superpositions sensitive to gravitational redshift. The resulting architecture implements a non-local Ramsey interferometer, where gravitationally induced phase shifts are imprinted on nonlocal entangled states and are read out through local measurements at the network nodes. Beyond extending the spatial reach of mass superpositions, our scheme establishes a scalable, programmable platform to probe the interface of quantum mechanics and gravity, and offers a new experimental pathway to test atom and atom-clock interferometer proposals, e.g. for probing gravitational dephasing, in a network-based quantum laboratory.
Video recording: https://youtu.be/a6EcHRpZWKs
Presentation slides: https://drive.google.com/file/d/1j-D8AkVk3TQoiK3pmnJFD4EA1QimEorD/view?usp=sharing
Date and time: 16 July 2026, 15:00 (CEST)
Speaker: Youka Kaku (Stevens Institute of Technology)
Title: Quantumness unique to gravity in quantum clock systems
Abstract: In 2017, several groups proposed testing whether Newtonian gravity can generate quantum entanglement between spatially superposed masses. This idea has attracted considerable attention as a possible low-energy test of the quantum nature of gravity. However, entanglement between spatial superposition states is not unique to gravity; it can also be generated by other interactions, such as the Coulomb interaction. In this talk, we shall discuss a quantum effect that is more specific to gravity. We focus on a quantum clock system, namely a particle with internal energy levels, which reveals various gravitational phenomena arising from mass-energy equivalence. We consider an atomic interferometer for the clock system under an external force generated by a spatially superposed source. As a result, we show that the collapse and revival of the interference visibility depend qualitatively on whether the external force is described by first-quantized Newtonian gravity, Schrödinger-Newton gravity, or the Coulomb interaction. This difference reflects in entanglement between the internal energy states of the clock and the spatial superposition state of the source. We show that this type of entanglement is generated uniquely by the first-quantized Newtonian gravity when the weak equivalence principle is respected.
This talk is based on Phys. Rev. D 106, 126005 (2022).
Video recording: https://youtu.be/f0qfs2Xy0l8
Presentation slides: https://drive.google.com/file/d/1gZu1dd5dQFoLxWrizzkBGbGzwmCZXH46/view?usp=sharing