## Information at all length scales

## from black holes to quantum information and living systems

## DIEP focus session on information theory | 18th January 2021| 10:35 - 11:55 | Online | Physics@Veldhoven

## Barbara Terhal

## Stephanie Wehner

## Greg Stephens

## Organizers and chairs: Jácome Armas and Michael Walter

## Erik Verlinde

## An invitation to information theory

###### Information plays a ubiquitous role in physics. Information-theoretic concepts such as entropy appeared for the first time in the context of classical thermodynamics and represent how information is encoded, stored and coarse-grained at given length scales. Historically, the study of information theory has revealed deep connections between microscopic physical degrees of freedom and large-scale macrophysics, providing an understanding, for instance, of the emergent properties of large collections of particles. Nowadays, information theory is an integral part of the study of the physics of complex and living systems, while its quantum counterpart, quantum information theory, has led to numerous discoveries in quantum technology and condensed matter systems and to insights into the physics of black holes. This focus session covers many of these developments, including applications to black hole physics and reconstruction of space and time, quantum information, large quantum/classical networks and information processing in living systems.

###### (We had an unfortunate cancellation by Xiaoliang Qi (Stanford University))

## Programme:

######

###### Quantum computational physics and quantum complexity theory aim at simulating quantum physical systems effectively or capturing the computational hardness of quantum physical problems. An important class of possibly 'easier' problems are quantum systems without a sign problem, sometimes referred to as stoquastic Hamiltonians. We discuss whether Hamiltonian descriptions of superconducting qubit devices, in particular of coupled flux qubits, do or do not have a sign problem and the computational consequences thereof for a task such as quantum annealing.

###### Stoquastic Hamiltonians in Circuit-QED

###### Barbara Terhal, TU Delft | 10:36-10:55

Building the first large-scale quantum network is a highly challenging endeavor. Not only is it a highly contested question of what the most promising hardware platform might be, but even if we had selected one, it is unknown what the precise requirements for its realization would be.

In this talk, we will present a series of methods that can be used in order to determine minimal requirements of creating such a network on an existing fiber network infrastructure. We start by presenting an algorithm to perform a pre-selection of where quantum repeaters may be located on an existing fiber grid. We present a purpose built discrete event simulator that can be used to validate candidate architectures, and a matching machine learning method that can be used to determine minimal hardware (or software) requirements necessary to achieve a specific target functionality of the network. Finally, we provide an initial case study of a resulting Blueprint for a network architecture on the real world fiber grid of SURF in the Netherlands.

###### Towards a Blueprint for a Quantum Internet

###### Stephanie Wehner, TU Delft | 10:55-11:15

######

###### Physics offers countless examples for which theoretical predictions are astonishingly powerful, such as the first detection of gravitational waves using near-atomic scale deformations in kilometer-scale interferometers. Unfortunately, it’s hard to imagine similar precision in complex systems, including life. The number and interdependencies between components of complex systems simply prohibits a first-principles approach: look no further than the challenge of the billions of neurons and trillions of connections within our own brains. Faced with such complexity how do we even compare theory and experiment? Here we describe an alternative, systems-scale perspective in which we integrate information theory, dynamical systems and statistical physics to extract understanding directly from measurements. We demonstrate our perspective first with a reconstructed state space of the behavior of the nematode worm C. elegans, revealing a low-dimensional chaotic attractor with symmetric Lyapunov spectrum. We then outline a maximally predictive, coarse-graining in which nonlinearities are subsumed into a linear, ensemble evolution to obtain a simple yet accurate model on multiple scales. We demonstrate this approach by identifying long timescales and collective states in the Langevin dynamics of a double-well potential and the Lorenz system. Our ``inverse’' perspective provides an emergent, quantitative framework in which to seek rather than impose effective organizing principles of complex systems.

###### Theory, reimagined

###### Greg Stephens, Vrije Universiteit Amsterdam | 11:15-11:35

###### Quantum Information and Black Holes

###### Erik Verlinde, UvA | 11:35-11:55

In recent years considerable progress has been made in the study of the quantum aspects of black holes, and the microscopic understanding of space and time.

A crucial role in these developments is played by quantum information theoretic concepts like quantum entanglement, quantum teleportation and quantum (error correcting) codes.

In this presentation I will give a brief overview of these developments.