Researchers have studied how light can be used to “see” the quantum nature of an electronic material. They managed to do that by capturing light in a net of carbon atoms and slowing it down so that it moves almost as slow as the electrons in the graphene. Then something special happens: electrons and light start to move in concert, unveiling their quantum nature at such large scale that it can be observed with a special type of microscope. 

The experiments were performed with ultra-high quality graphene. To excite and image the ultra-slow ripples of light in the graphene (also called plasmons), the researchers used a special antenna for light that scans over the surface at a distance of a few nanometers. With this near field nanoscope they saw that the light ripples on the graphene moved more than 300 times slower than light, and dramatically different from what is expected from classical physics laws. 

The work has been published in Science by ICFO researchers Dr. Mark Lundeberg and Dr. Achim Woessner, led by ICREA Prof. at ICFO Frank Koppens, in collaboration with Prof. Hillenbrand from Nanogune, Prof. Polini from IIT and Prof. Hone from Columbia University. 

In reference to the accomplished experiments, Prof. Koppens comments: “Usually it is very difficult to probe the quantum world, and to do so it requires ultra-low temperatures; here we could just “see” it with light and even at room temperature”. 

This technique now paves the way for exploring many new types quantum materials, including superconductors where electricity can flow without energy consumption, or topological materials that allow for quantum information processing with topological qubits. In addition, Prof. Hillenbrand states that “this could just be the beginning of a new era of near field nanoscopy”. 

Prof. Polini adds that “This discovery may eventually lead to understanding in a truly microscopic fashion the complex quantum phenomena that occur when matter is subject to ultra-low temperatures and very high magnetic fields, like the fractional quantum Hall effect” 

This work reveals that the mechanism that repairs errors in DNA is more efficient in the regions of genes that hold information for the production of proteins.

The basic structure of genes is divided into exons and introns. The former holds the genetic sequences required to synthesize proteins, while most of the sequence of the latter hold less important information.

When DNA is copied, the molecule called polymerase—responsible for replication—places one nucleotide after the other in the sister sequence following the original sequence, but from time to time the wrong nucleotide is incorporated, thus causing an error. These errors can be corrected by the DNA mismatch repair machinery.

We showed that in tumors, with functional DNA mismatch repair machinery, exonic regions exhibit lower number of somatic mutations than expected. This decrease is not due to purifying selection. Instead, it can be explained by the enhanced activity of mismatch repair in exons compared to introns, a fact demonstrated by the lack of decrease in a type of paediatric brain cancer characterised by bialellic mismatch repair deficiency. The results of this work also suggest that the enhanced activity of mismatch repair in exons may be driven by the higher exonic levels of histone marks (H3K36me3).

Mismatch repair system is conserved across evolution, which leads to the intriguing possibility that a combination of enhanced repair and purifying selection contributes to the observed lower exonic variation and divergence, both intra and inter-species. This has important implications for designing methods to study genic selection and for our understanding of the evolution of eukaryotic genes.