# Gravity, Quantum Fields and Information

How do gravitational force and matter at any point in space emerge from an underlying microscopic reality? How to model complex quantum mechanical systems with many constituents? What happens at a microscopic level when such systems evolve in time and how to quantify it? These are some of the motivating questions for the independent research group on “Gravity, Quantum Fields and Information” (GQFI) led by Dr. Michal P. Heller and generously supported by the Humboldt Foundation through the Sofja Kovalevskaja Award.

The theoretical framework underlying these questions is the holographic principle, i.e. a set of ideas originating from the field of black hole physics, which seek for the origin of gravitational force and the universe as a whole in terms of a lower-dimensional reality without gravitational interactions. In 1997 these ideas led to a very precise correspondence. On the one side, it involved some negatively curved universes and on the other a certain class of quantum field theories in a lower number of directions. This holography, also known as the AdS/CFT or the gauge/gravity duality, with time became a valuable ab-initio approach to quantum field theories. In particular, it allowed modeling equilibration processes similar to the ones occurring in ultra-energetic collisions of atomic nuclei at RHIC and LHC accelerators and brought many interesting phenomenological lessons in the field of nuclear physics [1-3].

A breakthrough result in 2006 demonstrated (see also [4]) that a very important role in the way negatively curved universes emerge from underlying quantum field theories is played by the information about entanglement between different sub-regions in these systems. The latter topic is the focal point of interest for quantum-many body physics and, cleverly used, allows for efficient simulations of complex quantum systems with many constituents. Furthermore, thinking about the physics of entanglement in quantum field theories has led to a fascinating link with other spacetimes, in particular de Sitter geometry of our Universe [5-6].

The aim of the GQFI independent research group is to explore the fascinating intersection of gravitational and high-energy physics with quantum information science. The topics of primary interest are equilibration phenomena in quantum field theories, the broadly-understood link between spacetime geometries and entanglement and entanglement-based approaches to quantum field theories.

[1] M. P. Heller, R. A. Janik, P. Witaszczyk, “The characteristics of thermalization of boost-invariant plasma from holography,” Phys. Rev. Lett. 108 (2012) 201602, arXiv:1103.3452 [hep-th]

[2] M. P. Heller, D. Mateos, W. van der Schee, D. Trancanelli, “Strong Coupling Isotropization of Non-Abelian Plasmas Simplified,” Phys. Rev. Lett. 108 (2012) 191601, arXiv:1202.0981 [hep-th]

[3] M. P. Heller, R. A. Janik, P. Witaszczyk, “Hydrodynamic Gradient Expansion in Gauge Theory Plasmas,” Phys. Rev. Lett. 110 (2013) 211602, arXiv:1302.0697 [hep-th]

[4] V. Balasubramanian, B. D. Chowdhury, B. Czech, J. de Boer, M. P. Heller, “Bulk curves from boundary data in holography,” Phys. Rev. D89 (2014), 086004, arXiv:1310.4204 [hep-th]

[5] J. de Boer, M. P. Heller, R. C. Myers, Y. Neiman, “Holographic de Sitter Geometry from Entanglement in Conformal Field Theory,” Phys. Rev. Lett. 116 (2016), 061602, arXiv:1509.00113 [hep-th]

[6] J. de Boer, F. M. Haehl, M. P. Heller, R. C. Myers, “Entanglement, holography and causal diamonds,” JHEP 1608 (2016) 162, arXiv:1606.03307 [hep-th]