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Link visio: https://univ-grenoble-alpes-fr.zoom.us/j/97827988665?pwd=fOb8WVvg3kBHPaGbGLvVQP84zMp1S6.1
The defence will be in English.
Abstract: Waveguide QED refers to the physics of quantum emitters coupled to reservoirs of light modes confined in one dimension, such as superconducting and photonic circuits. Owing to constant technological improvements it is now possible to measure the state of the light with high efficiency. These new experimental capacities mandate to update theoretical tools, to close formerly open quantum systems. This is the purpose of Autonomous Collisional Models (ACM). They model the emitter-field interaction as repeated interactions in a closed manner, with no external influence. By construction, an ACM captures the unitary dynamics of the quantum emitter and the light modes, unlocking access to their correlations. Moreover, they are energy conserving and give rise to a thermodynamics framework with symmetric and accurate energy balances between quantum systems.
We first build an ACM to describe a qubit coupled to a displaced thermal field, which is the regime of the Optical Bloch Equations (OBE). Through this study, we track fundamental correlations created within each collision and in doing so find that each sub-system is driven by an effective Hamiltonian while a remnant term captures the effect of the correlations. They respectively impact the field amplitude and fluctuations, resulting in a physically observable splitting. We then explore the thermodynamic consequences of our framework by developing a general paradigm valid for any isolated bipartite system, i.e., bipartite quantum energetics (BQE). Exploiting the global energy conservation, we define work-like (heat-like) flows as the energy changes stemming from the effective Hamiltonian dynamics (the dynamics induced by the correlations). We show that these quantities are accessible through measurements performed on the field, such as dyne or spectroscopic measurements. Our approach differs from former analyses by the emitter self-work, which yields a tighter expression of the second law. We quantitatively relate this tightening to the extra-knowledge about the field, compared with usual treatment of the atom as an open system.
Lastly, to extract intuitions about the energetic impact of correlations, we apply BQE to the interaction of light fields within a BS. It reveals that the energies exchanged are directly measurable in the fields’ phase-space distributions. We find that the field is deformed whenever heat-like energy is exchanged, while displacements are caused through transfer of work-like energy. We again find a tightening of the second law and show that in this framework squeezing can transfer heat from a colder to a hotter field, while maintaining a positive entropy production. The concepts and effects we introduce deepen our understanding of thermodynamics in the quantum regime and its potential for energy management at quantum scales.
