The goal of this physics school is to offer master and Ph.D. students from the field of experimental and theoretical physics as well as mathematics and philosophy a coherent introduction to the subject of quantum gravity in low energy quantum systems from both theoretical and experimental perspectives. 

The participants will receive training in the theoretical description of quantum system under the influence of gravity and how to predict observable signatures. They will learn how specific experimental setups can be used to test the theoretical predictions. This education equips the participants with the skills to bridge the gap between theory and experiment in the field of the interplay between quantum systems and classical and quantum gravity research in the future.

This is the second of a series of Training Schools organized by the European COST Action CA23130 - BridgeQG: Bridging high and low energies in search of quantum gravity (https://web.infn.it/BridgeQG).

While the focus of the first training school was on the high-energy aspects of the BridgeQG research topics, the focus of this training school will be on the low-energy aspects.

A third school will cover the combination of the two branches.

The school consists of four main lectures, which are accompanied by tutorial classes. In addition there will be an introductory short lecture on quantum gravity phenomenology, and a concluding short lecture. Lecture notes will be published after the school.

Lecturers and topics (Final titles of the lectures will be announced soon)

Časlav Brukner: Quantum clocks and Quantum Reference Frames for Quantum Gravity

Rainer Kaltenbaek: Testing Quantum Physics in Space

Sofia Qvarfort: Quantum Metrology and the Standard Quantum Limit

In these lectures, we will cover quantum and classical Fisher information as a tool for quantifying the sensitivity of quantum systems. We will then also look at the fundamental limits of positions measurements, which are key for e.g. gravitational wave measurements, and which leads to the Standard Quantum Limit. 

Benjamin Stickler: Quantum control of optically trapped nanoparticles

Simone Manti: Testing quantum gravity with underground experiments

Quantum mechanics provides an extraordinarily successful description of microscopic phenomena, yet fundamental questions remain open. Among the most important are the origin of wave function collapse, embodied in the measurement problem, and the exact validity of the Pauli Exclusion Principle, one of the cornerstones of quantum theory. In this talk, I will present a program of precision experiments conducted at the underground laboratories of INFN Laboratori Nazionali del Gran Sasso, designed to probe possible deviations from standard quantum mechanics in ultra-low-background conditions. Using state-of-the-art radiation detectors, we search for two classes of rare phenomena: spontaneous electromagnetic emission predicted by dynamical collapse models, proposed as physically motivated solutions to the measurement problem and potentially connected to gravity, and Pauli-forbidden atomic transitions, which would signal violations of fermionic quantum statistics. I will discuss recent experimental results placing increasingly stringent bounds on Continuous Spontaneous Localization and related collapse scenarios, including tests motivated by gravity-induced collapse frameworks. I will also present the latest advances of the VIP Collaboration in high-sensitivity searches for possible violations of the Pauli Exclusion Principle. Together, these studies open a unique experimental window on quantum foundations, connecting precision measurements, underground rare-event searches, and emerging ideas at the interface between quantum theory and gravity.

Djordje Minić: Quantum Spacetime, Quantum Gravity, and Gravitized Quantum Theory, based on https://arxiv.org/pdf/2604.19418 and https://arxiv.org/abs/2407.06207

Lin-Qing Chen: Theoretical aspects of tabletop tests of quantum gravity

About COST Action CA23130 BridgeQG

Recent advances in both high-energy astrophysics and high-precision table-top experiments are pushing our capability to test nature in regimes where gravity meets quantum physics. Astrophysical observations are now potentially sensitive to tiny residual effects of Planck-scale physics, while table-top experiments are reaching the precision needed to test the interplay between gravity and quantum systems at ultra-low energies. Investigations of these regimes, in particular once they are combined, will provide important clues towards the understanding of the full-fledged theory of quantum gravity.

The main aim of the Action is to bring together scientists with a variety of complementary expertise: theorists working on quantum gravity or the interplay between gravity and quantum physics with quantum information and quantum optics tools, and experimentalists involved in astrophysical searches for quantum gravity, or investigating the effects of gravitational interactions on quantum systems. The resulting interdisciplinary collaboration will develop a common language and a shared framework which will boost investigations at the interface between high-energy quantum gravity and quantum aspects of gravity in the weak-field regime. The Action will also facilitate cross-disciplinary training and exposure of young scientists to different communities with a common goal, serving as a career accelerator. The synergy within this newly-formed community will be essential to systematically search for quantum gravity on all scales, and possibly find the first signatures of new physics.

J. Bolmont (LPNHE, Paris, France), L.-Q. Chen (Vienna U, Austria), C. O. Curceanu (INFN-LNF, Italy),  A. Domi (ECAP Erlangen-Nürnberg U, Germany), M. Fadel (ETH Zürich, Switzerland), T. Galley (IQOQI Vienna, Austria), F. Giacomini (ETH Zürich, Switzerland), G. Gubitosi (U Napoli Federico II, Italy), F. Mercati (Burgos U, Spain), A. Platania (Graz University, Austria), C. Pfeifer (ZARM, Bremen U, Germany), G. Rosati (U Cagliari, Italy), D. Staicova (INRNE, Bulgaria), J. Strišković (Osijek U, Croatia), T. Terzic (Rijeka U, Croatia), M. Tórtola (Valencia U, Spain)

Acknowledegments

This conference is supported by COST (European Cooperation in Science and Technology). COST is a funding agency for research and innovation networks. COST Actions help connect research initiatives across Europe and enable scientists to grow their ideas by sharing them with their peers. This boosts their research, career and innovation.