Information eNergy Conversion at the single quAntum Level – INCAL

« Information is physical » : by postulating the physical nature of information in 1961, Landauer was solving the paradox of Maxwell’s demon and successfully merging thermodynamics and information sciences. Of particular relevance is Landauer’s limit, which sets the smallest possible amount of work necessary to erase one bit of information, whereas reversibly, one bit of information can be converted into useful work (Szilard’s engine). Later in the nineties, the developments of quantum information shed novel light on entanglement, which appeared as a resource allowing to communicate more securely and to compute more efficiently than in the classical world. Recently, the peculiarities of quantum information started to be explored within a thermodynamical paradigm. Oddly enough, it was shown that the erasure of a bit could produce work provided that the observer is quantum, a drastic difference with respect to classical information.

Owing to the progresses of nanotechnologies, Landauer’s limit and Szilard’s engine have recently been experimentally demonstrated with classical bits. However, thermodynamics of quantum information has remained restricted to theoretical investigations so far, involving rather abstract notions of small systems, thermal baths and batteries. The purpose of the present project is to give a physical identity to these notions, and to suggest and model experiments in this new field, in close interaction with experimental groups. Feasibility studies will be conducted for two different systems, both having already shown outstanding results in the domain of quantum information processing, namely Josephson qubits in circuit QED (case 1) and solid-state emitters in optomechanics (case 2).

As a first step, we will build the conceptual and modeling tools to describe a heat engine operating at the single quantum level. We will particularly focus on extensively characterizing the work produced by the machine, that will either consist of tiny electromagnetic (case 1) or phononic fields (case 2). This is drastically new with respect to former estimations of the thermodynamical quantities, so far based solely on measurements performed on the small working system itself. This approach relies on the ability to monitor continuously such environments as transmission lines or phononic fields, an ability that we plan here to exploit for the first time in a thermodynamical context. This study should lead to the first direct measurement of Landauer’s limit.

As a second step, we will study the potential of each system as a platform to investigate new physical effects related to quantum information and entanglement. In this perspective, heat engines involving two quantum bits will be modeled. In particular, we will explore to which extent the useful energy extracted from the engine can be used to quantify the strength of the correlations between the two qubits. A final product of these fundamental investigations could be a heat engine working as entanglement witness.

The success of the present project will contribute to create an important synergy between a wide range of scientific communities : quantum optics, quantum information, thermodynamics, circuit QED and optomechanics. It will benefit from the collaboration with a high level team working on theoretical aspects of the thermodynamics of quantum information, and aims at developping a local think tank around these groundbreaking ideas, in direct connection with experimentalists. From a deeper point of view, this project will bring out the first building blocks for the comprehension of information/energy conversion at the nanoscale, a fundamental issue in our society of information.