Quantum thermometry at ultracold temperatures (Ref: 4342-6)

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Quantum thermometry is a rapidly growing field aimed at establishing precision limits on thermometry when quantum effects are important. Strong dissipative interactions at low temperatures can create quantum correlations between a temperature probe and the measured sample. In order to accurately describe the state of the probe, one may resort to the theory of open quantum systems. The thermal sensitivity of the probe can be then quantified with the toolbox of quantum estimation theory. This provides a robust theoretical framework to study thermometry experiments. Given the stringent limitations on ultracold measurements, it is essential to understand the origin of these bounds, and harness that understanding to optimise current experiments. Quantum thermometry appears as the ideal vehicle to achieve it.The core objective of this theoretical project is to develop new theory that will help integrate quantum thermometry into current low-temperature experiments. To do so, we will blend the powerful microscopic modelling from the theory of open quantum systems with Bayesian estimation methods. We will use this new framework to devise upgrades to experimental thermometric techniques and to boost their precision and time-efficiency. To do so, we will reformulate recently developed Bayesian methods for use in out-of-equilibrium situations. This will facilitate optimal and platform-independent processing of noisy data in situations of particular experimental interest-extreme temperatures and finite couplings. The outcomes will thus be relevant for thermal control on cold-atom based technologies, but also trapped ions, superconducting qubits, or quantum optomechanics. The theory of open quantum systems and thier thermodynamic characterisation will be the second major player in this projetc. It provides an effective and tractable approximation to the dynamics of individual quantum systems in contact with their surroundings. While much effort has gone into studying the thermodynamics of open systems in weak thermal contact with linear baths, the regimes of non-linear and strong dissipation still remain virtually unexplored. These are likely to unveil rich new physics, as well as offering a plethora of opportunities for boosting the energetic performance of quantum-thermodynamic devices. Besides, accurate modelling of real-life devices certainly requires going beyond weak linear dissipation. However, this will require a whole set of new/repurposed open-system tools based on, e.g., Markovian embedding methods, perturbative expansions of global equilibrium states, or truncation of hierarchies of exact equations of motion.