Thermodynamic constraints on noise

Doctoral thesis, 2025

The recent progress in nanotechnology has allowed the fabrication of smaller and smaller devices.
On the one hand, this development allows to fit more of such devices on a chip, improving its performance.
On the other hand, decreasing the size of the device allows the emergence of new phenomena, such as quantum effects and sizable fluctuations.
Indeed, when the size of the device is comparable with the coherence legth, the quantum nature of particles cannot be neglected. Furthermore, the smaller a device is, the more it is affected by random changes in one of its few components, leading to fluctuations and noise that are comparable with the average quantities.
While these phenomena pose new challenges, they also offer new opportunities both in terms of understanding the underlying physical system, and of realizing new devices that exploit such phenomena.

This thesis studies, from a theoretical perspective, the noise in such nanodevices where both quantum effects and fluctuations play an important role.
While noise has already been investigated for systems at thermodynamic equilibrium, most devices need to operate out of equilibrium in order to be useful. Here we show that such out-of-equilibrium conditions set constraints on how large or how small the noise can be, and how these constraints affect the performance of the device.