# Decoherence and the quantum-to-classical transition for complex systems

Quantum theory is the current framework that is used to understand the fundamental constituent of the Universe. Contrary to classical physics, it has many non intuitive features rooted in the superposition principle and embodied in the famous SchrÃ¶dinger's cat paradox. What this paradox illustrates are the difficulties to apply quantum concepts into our classical world and naturally leads to the question of how to understand the quantum-to-classical transition.

Decoherence is our best physical mechanism to understand this quantum to classical transition. From a conceptual perspective, the underlying idea behind this phenomenon is that every system is never isolated from an unmonitored environment, whatever care the experimentalist is putting in the design of their experiment. Information about the state of the system is always lost in the environment and this leakage leads to the effective destruction of the quantum interference pattern.

To be more precise, what controls the decoherence process and the emergence of a classical description is mostly the interaction between the system and its environment. In principle, once we know the interaction, we could determine how the transition occurs. In practice, the most efficient approach is to set up a simple effective model, like the quantum Brownian motion, and compare it to our experiments. In realistic cases, however, the environment will be composed of different parts competing to access the limited information stored in the quantum system. In those cases, even when the dynamics is well known, the question of the emerging classical states can be deeply non trivial.

The goal of this project is to have a better understanding of the emerging classical states when a system is interacting with complex, competing environments.

# Outcome

*arXiv preprint arXiv: 2001.10851*