# Theoretical Physics Seminar: Friederike Metz

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This is the 20th biweekly session of the OIST Theoretical Physics Seminar.

In this seminar series, we pretend to have a theoretical physics department, and tell each other informal stories over drinks and snacks.

Speaker: Friederike Metz (Quantum Systems).

Title: "Precise temperature estimation with a single qubit as a probe".

With the increasing number of experiments and technologies involving quantum systems, grows the need for precise control and monitoring thereof. Many of those quantum systems such as ultracold atomic gases operate at extremely low temperatures and therefore very precise temperature estimation protocols become inevitable. On the other hand, quantum effects allow us to infer the temperature in completely new ways that do not necessarily rely on the energy transfer (thermalization) of a probe with the environment. For example, when coupling a qubit to the system of interest, its temperature is encoded in the dephasing dynamics of the qubit. Hence, measurements of the qubit alone can reveal the temperature of the system without the need of destructively measuring the system itself.

In this seminar I will introduce the basics of (quantum) parameter estimation theory which lays the foundations for temperature estimation and its precision bounds. Then, I will introduce a particular system as an example which consist of a gas of fermionic particles and a single qubit whose coupling strength to the gas can be changed in a controlled way. I will show how the coherences of the qubit (the off diagonal elements of its density matrix) encode the temperature of the gas. In case I have time, I will tell you how I want to improve the precision of the temperature estimation using machine learning.

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