New understanding of the limits on nano-noise

Nanotechnology is rapidly advancing, capturing widespread interest across industries 
such as communications and energy production. At the nano level – equivalent to a 
millionth of a millimeter – particles adhere to quantum mechanical laws. By harnessing 
these properties, materials can be engineered to exhibit enhanced conductivity, 
magnetism, and energy efficiency.

“Today, we witness the tangible impact of nanotechnology – nanoscale devices are 
ingredients to faster technologies and nanostructures make materials for power 
production more efficient,” says Janine Splettstoesser, Professor of Applied Quantum 
Physics at Chalmers.

Devices smaller than the human cell unlocking novel electronic and 
thermoelectric properties

To manipulate charge and energy currents down to the single-electron level, 
researchers use so-called nanoscale devices, systems smaller than human cells. These 
nanoelectronic systems can act as “tiny engines” performing specific tasks, leveraging 
quantum mechanical properties.

“At the nanoscale, devices can have entirely new and desirable properties. These 
devices, which are a hundred to ten thousand times smaller than a human cell, allow to 
design highly efficient energy conversion processes,” says Ludovico Tesser, PhD student 
in Applied Quantum Physics at Chalmers University of Technology. 

Navigating nano-noise: a crucial challenge

However, noise poses a significant hurdle in advancing this nanotechnology research. 
This disruptive noise is created by electrical charge fluctuations and thermal effects 
within devices, hindering precise and reliable performance. Despite extensive efforts, 
researchers have yet to find out to which extent this noise can be eliminated without 
hindering energy conversion, and our understanding of its mechanisms remains limited. 
But now a research team at Chalmers has succeeded in taking an important step in the 
right direction.

In their recent study, published as editor’s suggestion in Physical Review 
Letters, they investigated thermoelectric heat engines at the nanoscale. These 
specialised devices are designed to control and convert waste heat into electrical 
power.

“All electronics emit heat and recently there has been a lot of effort to understand how, 
at the nano-level, this heat can be converted to useful energy. Tiny thermoelectric heat 
engines take advantage of quantum mechanical properties and nonthermal effects and, 
like tiny power plants, can convert the heat into electrical power rather than letting it go 
to waste,” says Professor Splettstoesser.

Balancing noise and power in nanoscale heat engines

However, nanoscale thermoelectric heat engines work better when subject to 
significant temperature differences. These temperature variations make the already 
challenging noise researchers are facing even trickier to study and understand. But now, 
the Chalmers researchers have managed to shed light on a critical trade-off between 
noise and power in thermoelectric heat engines.

“We can prove that there is a fundamental constraint to the noise directly affecting the 
performance of the "engine. For example, we can not only see that if you want the 
device to produce a lot of power, you need to tolerate higher noise levels, but also the 
exact amount of noise. It clarifies a trade-off relation, that is how much noise one must 
endure to extract a specific amount of power from these nanoscale engines. We hope 
that these findings can serve as a guideline in the area going forward to design 
nanoscale thermoelectric devices with high precision,” says Ludovico Tesser.

More about the research:
The study “Out-of-Equilibrium Fluctuation-Dissipation Bounds” was published in 
Physical Review Letters, on 3 May 2024

Funding: 
The research project has been funded by the European Research Council (ERC) under the European Union’s Horizon Europe research and innovation program (101088169/NanoRecycle), as well as by a Wallenberg Academy Fellowship.