# Zenith Grant Awardee

## Benjamin Huard

### Ecole Normale Supérieure de Lyon

Co-Investigators

Sergio Ciliberto, École Normale Supérieure de Lyon

Project Title

Information as fuel in colloids and superconducting quantum circuits

Project Summary

This project aims at performing groundbreaking experiments to explore the relation between information, irreversibility and energy. This fundamental question lies at the crossroads of statistical physics, quantum mechanics and philosophy. It is the field of information thermodynamics.

The concept of information as a fuel can be traced back to the paradox phrased by Maxwell two centuries ago. Maxwell imagined an entity, called a demon, that observes a system and uses the information it acquired to realize feats that are seemingly forbidden by the laws of nature (in this case, the second law of thermodynamics). For instance, using the information about the system, the demon can create an engine that works without heating one part of the environment or a cooler that cools down a system for free. The paradox was solved a century later, by understanding that the measurement and information storage by the demon need to be accounted for.

Despite its fundamental and practical interest, the field of information thermodynamics is still in its infancy with very few experiments. Energetic footprints associated to the processing of classical information have been observed only recently. Besides, the burst of quantum information technologies has raised new questions.

Is quantum information a new type of fuel leading to a thermodynamic advantage of quantum Maxwell demons with respect to their classical counterparts? Is it possible to design a Maxwell demon that operates in full autonomy and in the classical macroscopic limit? How is information defined in this regime? Our project plans to answer several similar questions, building on a strong consortium of experimentalists and theorists having brought major contributions in the field, and taking advantage of mature experimental platforms. Our interdisciplinary approach paves the way towards a unified framework for Maxwell's demons, from the deep quantum regime where coherence and entanglement matter, to the classical, macroscopic regime where the mere concept of information must be defined. In particular, we will show that the inherent backaction of a measurement on a quantum system provides a new form of energy resource for engines. We will demonstrate the existence of this resource directly using superconducting circuits and use it for two kinds of Maxwell demons. Besides, we will use colloids and electrical circuits to show new types of autonomous Maxwell demons in the classical limit.

Technical Abstract

This project aims at performing groundbreaking experiments to explore the relation between information, irreversibility and energy. This fundamental question lies at the crossroads of statistical physics, quantum mechanics and philosophy. Information thermodynamics provides a framework to investigate these concepts at the ultimate level where systems are elementary carriers of information (bits).

Despite its fundamental and practical interest, the field is still in its infancy. Energetic footprints associated to the processing of classical information have been observed only recently. Besides, the burst of quantum information technologies has raised new questions, such as for example on the role played by superposition and entanglement, which might be energetic resources useful for outperforming classical thermal engines and coolers.

Is quantum information a new type of fuel leading to a thermodynamic advantage of quantum Maxwell demons with respect to its classical counterparts? Is it possible to design a Maxwell demon that operates in full autonomy and in the classical macroscopic limit? How is information defined in this regime? Here we plan to answer several similar questions, building on a strong consortium of experimentalists and theorists having brought major contributions in the field, and taking advantage of mature experimental platforms. Our interdisciplinary approach paves the way towards a unified framework for Maxwell's demons, from the deep quantum regime where coherence and entanglement matter, to the classical, macroscopic regime where the mere concept of information must be defined.

1) In the quantum regime, it is well known that measurement disturbs the state of the measured system, possibly changing its energy. Observing a quantum system thus induces energetic fluctuations of purely quantum nature (quantum noise) that have been dubbed quantum heat. We will realize the first experiment to directly measure the quantum heat and its origin within a superconducting circuit. The concepts developed along this research line will be the soil of philosophical investigations related to the thermodynamical implications of the measurement postulate.

2) We will implement two quantum Maxwell demons that convert the quantum heat into useful work. We here benefit from the unique experimental ability to measure work directly, in the form of amplified microwave radiation reflected off a superconducting circuit. Our experiments will provide a clear demonstration that quantum measurement is a new kind of fuel specific to the quantum regime. Two flavors of demons will be realized: a non-autonomous demon using an electronic circuit called a Field Programmable Gate Array and an autonomous demon using microwave modes that act as a controller and detector in situ.

3) We will design and realize fully autonomous Maxwell demons based on a macroscopic classical system. One will be based on electrical circuits and the other one on colloids acting as Brownian particles. Using a parametric driving, we will engineer a non-linear interaction between a system and a demon such that the system is cooled down. We will analyze the energy flows and the correlations between system and demon to extend the notion of information as a fuel for a continuum of states.