Smalltalks "How much noise is necessary in mesoscopic engines?"

Abstract: 

Noise plays an important role in the characterization of nanoscale systems because, due to their small size, fluctuations are often comparable with average quantities.

In this talk, I will discuss some general properties of noise in coherent mesoscopic conductors. These properties can be formulated as inequalities, setting bounds on the noise. For example, when the device is working as an engine, they result in inequalities between the noise and useful output, e.g. output power.

First, I will discuss the main differences between conventional, macroscopic engines and mesoscopic ones. The key distinctions lie in the presence of non-negligible fluctuations and quantum mechanical features. In classical systems, fluctuations play a crucial role in determining the maximum output power in nanoscale engines. This is quantified by the recently developed thermodynamic uncertainty relations [1], which set a constraint on the precision of the engine. However, these uncertainty relations hold no longer in the presence of quantum coherence. Nonetheless, we establish a novel relation between the average charge current flowing in a mesoscopic conductor where quantum coherence is present and its noise [1]. This result sets a minimum amount of noise required to produce power, which complements the thermodynamic uncertainty relation.