Mixing light with dye molecules, trapped in golden gaps. Credit: Yi Ju/University of Cambridge NanoPhotonics
Researchers have successfully used quantum states to mix a molecule with light at room temperature, which will aid in the exploration of quantum technologies and provide new ways to manipulate the physical and chemical properties of matter, aid in understanding photosynthesis mechanisms, or manipulate chemical bonds between atoms.
When a molecule emits a blink of light, it doesn’t expect it to ever come back. However researchers have now managed to place single molecules in such a tiny optical cavity that emitted photons, return to the molecule before they have properly left. The energy oscillates between light and molecule, resulting in a complete mixing. Previous attempts to mix molecules with light have been complex and only at very low temps, but the researchers, led by Uni of Cambridge, can now produce ‘half-light’ molecules at room temperature.
They constructed cavities 1nm across in order to trap light. They used the tiny gap between a gold nanoparticle and a mirror, and placed a coloured dye molecule inside. “It’s like a hall of mirrors for a molecule, only spaced a hundred thousand times thinner than a human hair,” said Prof Jeremy Baumberg of the NanoPhotonics Centre.
To achieve the molecule-light mixing, the dye molecules needed to be correctly positioned in the tiny gap. “Our molecules like to lie down flat on the gold, and it was really hard to persuade them to stand up straight,” said Rohit Chikkaraddy. To solve this, the team joined with a team of chemists at Cambridge to encapsulate the dyes in hollow barrel-shaped molecular cages called cucurbiturils, which are able to hold the dye molecules in the desired upright position.
When assembled together correctly, the molecule scattering spectrum splits into 2 separated quantum states, the signature of this ‘mixing’. This spacing in colour corresponds to photons taking less than a trillionth of a second to come back to the molecule. A key advance was to show strong mixing of light and matter was possible for single molecules even with large absorption of light in the metal and at room temperature. They could observe steps in the colour spacing of the states corresponding to whether 1, 2, or 3 molecules were in the gap. http://www.cam.ac.uk/research/news/nano-hall-of-mirrors-causes-molecules-to-mix-with-light
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