# Qubits and Spacetime Unit (Philipp Höhn)

The challenge of quantum gravity is to build a theory valid over all the scales down to the minuscule Planck scale, which explains how the known physics of general relativity and quantum (field) theory emerge from it. This deep challenge is the main impetus of the research efforts of the Qubits and Spacetime Unit.

There are many approaches to quantum gravity, and, rather than adhering to a specific one, we pursue somewhat of an "approach-independent approach". This means that our focus lies on generic challenges, which many approaches to quantum gravity will have to face up to and which have implications and relevance also in other areas of physics. Thus, we focus less on Planck scale physics and more on effective descriptions in quantum gravity that are closer to the known physics. The idea is to develop concepts, tools and methodology, which will be useful for various approaches to quantum gravity and beyond, e.g., for classical gravity, gauge theories, quantum information and the foundations of quantum theory, but we also import ingredients from the latter areas. Our research therefore resides at the interface of a broad spectrum of topics in fundamental physics and this is also reflected in the composition of our Unit. In particular, we host and have hosted representatives from different approaches to quantum gravity, as well as from quantum foundations and quantum information theory.

A main tool which we have been developing recently is that of quantum reference frames. These are internal frames associated with quantum subsystems and appear in any quantum system subject to a symmetry principle. As such, they are relevant in all of the above mentioned areas, as well as in quantum thermodynamics. While we have explored them in all of these contexts, we are especially interested in their application to gauge theories and gravity, whose physical content they define via dressed/relational observables. For example, we are interested in finite regions and subsystems in gauge theory and gravity, where quantum frames help to define and regulate entanglement entropies. Quantum frames further give rise to a novel quantum covariance of physical properties and laws that we study. However, we also research on other topics, including spacetime thermodynamics and quantum error correcting codes in high-energy physics.

**We're hiring a new postdoc:**

A 2+1 year postdoctoral position will become available in the fall of 2024, with (non-sharp) deadline July 1st. For more information, click here.

__2 workshops @ OIST in the fall of 2024, co-organized by our unit:__

### 1) QG/QI/QMB Workshop 2024 with the Extreme Universe Collaboration

#### Click here for more info.

#### Registration deadline: June 20th, 2024.

### 2) From Quantum Materials to Quantum Information (QMQI2024): Nov 11 - 15, 2024

Interdisciplinary symposium co-organized with the Quantum Materials Synthesis collaboration, funded by the Gordon and Betty Moore Foundation, and the Trans-Scale Quantum Science Institute of the University of Tokyo. This event will bring together researchers from quantum many-body physics, quantum materials science, quantum computation, quantum information and the foundations of quantum theory.

#### Click here for more info.

#### Registration/application deadline: July 17th, 2024.

## Some recent recorded overview talks:

- Philipp Höhn, "Quantum frames, subsystems and gravity", 9 Nov 2023, gravity seminar @ KITP/UC Santa Barbara (video)
- Philipp Höhn, "Quantum frames and subsystems", 13 Sep 2023, Extreme Universe -YITP
*Workshop on Holography, Gravity and Quantum Information*, workshop @ YITP Kyoto (video) - Philipp Höhn, "Complementarity identities from an informational reconstruction", Aug 1 2023,
*The Quantum Reconstruction Program and Beyond,*workshop @ U Graz (video) - Philipp Höhn, "Observables and dynamical frames in gravity", 11 July 2023,
*QG2023*, conference @ U Nijmegen, (video) - Philipp Höhn, "Quantum frame covariance and subsystem relativity", May 24 2023,
*Quantum Information and Quantum Matter*, workshop @ NYU Abu Dhabi (video) - Philipp Höhn, "Dynamical frames in gauge theory and gravity", 26 Sep 2022,
*Quantum extreme universe from quantum information, workshop @ YITP Kyoto*(video) & 22 Sep 2022,*QG seminar @ Perimeter Institute*(video) - Philipp Höhn, "Dynamical frames in gravity: locality, covariance and charges", 1 July 2022,
*Gravity Seminar*@*University of Vienna*(video)

## New articles:

- Julian De Vuyst, Stefan Eccles, Philipp A. Höhn and Josh Kirklin, "Gravitational entropy is observer-dependent", arXiv:2405.00114
- Elena Cáceres, Stefan Eccles, Jason Pollack and Sarah Racz, "Generic ETH: eigenstate thermalization beyond the microcanonical", arXiv:2403.05197
- Salvatore Ribisi and Francesco Sartini, "Phase spaces and symmetries of Vaidya superspace", arxiv:2401.16036
- Aidan Chatwin-Davies, Pompey Leung and Grant N. Remmen, "Holographic screen sequestration", arXiv:2312.06750
- Philipp A. Höhn, Andrea Russo and Alexander Smith, "Matter relative to quantum hypersurfaces",
*Phys. Rev.**D***109**, (2024) 105011, arXiv:2308.12912 - Philipp A. Höhn, Isha Kotecha and Fabio M. Mele, "Quantum Frame Relativity of Subsystems, Correlations and Thermodynamics", arXiv: 2308.09131
- Josh Kirklin, "Probes, purviews, purgatories, parable, paradox?", arXiv: 2304.00679

## Currently Taught Courses (more info):

- Quantum many-body physics (lecturer Prof. P. Höhn)