31 March 2014 Never say never in the nano world

Artistic impression of a nano-particle trapped by a laser

Temporal violation of the second law of thermodynamics in Nature Nanotechnology. Objects with sizes in the nanometer range, such as the molecular building blocks of living cells or nanotechnological devices, are continuously exposed to random collisions with surrounding molecules. In such fluctuating environments, the fundamental laws of thermodynamics that govern our macroscopic world need to be rewritten.

An international team of researchers from ICFO- The Institute of Photonic Sciences in Barcelona, the Swiss Federal Institute of Technology in Zurich and the University of Vienna found that a nanoparticle trapped with laser light temporarily violates the famous second law of thermodynamics, something that is impossible on human time and length scale. They report about their results in the latest issue of the prestigious scientific journal Nature Nanotechnology.

With their experimental set-up, the researchers were able to capture the nano-sphere and hold it in place, and, furthermore, to measure its position in all three spatial directions with exquisite precision. In the trap, the nano-sphere rattles around due to collisions with surrounding gas molecules. By a clever manipulation of the laser trap the scientists cooled the nano-sphere below the temperature of the surrounding gas and, thereby, put it into a non-equilibrium state. They then turned off the cooling and watched the particle relaxing to the higher temperature through energy transfer from the gas molecules.

The researchers observed that the tiny glass sphere sometimes, although rarely, does not behave as one would expect according to the second law: the nano-sphere effectively releases heat to the hotter surroundings rather than absorbing the heat. The theory derived by the researchers to analyze the experiment confirms the emerging picture on the limitations of the second law on the nanoscale.