Even empty gaps have a colour. Now scientists have shown that quantum jumps of electrons can change the colour of gaps between nano-sized balls of gold. The new results, published today in the journal Nature, set a fundamental quantum limit on how tightly light can be trapped.
The team from the Universities of Cambridge, the Basque Country and Paris have combined tour de force experiments with advanced theories to show how light interacts with matter at nanometre sizes. The work shows how they can literally see quantum mechanics in action in air at room temperature.
Because electrons in a metal move easily, shining light onto a tiny crack pushes electric charges onto and off each crack face in turn, at optical frequencies. The oscillating charge across the gap produces a 'plasmonic' colour for the ghostly region in-between, but only when the gap is small enough.
Team leader Professor Jeremy Baumberg from the University of Cambridge Cavendish Laboratory suggests we think of this like the tension building between a flirtatious couple staring into each other's eyes. As their faces get closer the tension mounts, and only a kiss discharges this energy.
In the new experiments, the gap is shrunk below 1nm (1 billionth of a metre) which strongly reddens the gap colour as the charge builds up. However because electrons can jump across the gap by quantum tunnelling, the charge can drain away when the gap is below 0.35nm, seen as a blue-shifting of the colour. As Baumberg says, "It is as if you can kiss without quite touching lips."
Matt Hawkeye, from the experimental team at Cambridge, said: "Lining up the two nano-balls of gold is like closing your eyes and touching together two needles strapped to the end of your fingers. It has taken years of practise to get good at it."
Prof Javier Aizpurua, leader of the theoretical team from San Sebastian complains: "Trying to model so many electrons oscillating inside the gold just cannot be done with existing theories." He has had to fuse classical and quantum views of the world to even predict the colour shifts seen in experiment.
The new insights from this work suggest ways to measure the world down to the scale of single atoms and molecules, and strategies to make useful tiny devices.
The paper 'Capturing the Quantum Regime in Tunneling Plasmonics' will be published in the 07 November edition of Nature. Further information can be found at Nature: doi:10.1038/nature11653
University of Cambridge: http://www.cam.ac.uk
This press release was posted to serve as a topic for discussion. Please comment below. We try our best to only post press releases that are associated with peer reviewed scientific literature. Critical discussions of the research are appreciated. If you need help finding a link to the original article, please contact us on twitter or via e-mail.
Sheets of programmable matter can be made to pop into complex 3D shapes 100 times taller than their original thickness when heated, and could find uses in medicine
A particle physics student has used his downtime to build a Lego model of the world's most powerful particle accelerator, the Large Hadron Collider (LHC), and is now lobbying the toy company to take it to market.
Get the full the story behind a $761 jar of peanut butter and other exorbitantly priced everyday objects used by scientists
Satellite imagery shows 20 new craters around holes discovered last year in Siberia
Young maths whizz from Iran uses simple equations to paint stunning images that bizarrely look like marine objects, and makes a fractal Africa
A new breed of the hyper-accurate clocks could help scientists detect the elusive ripples in space-time faster and cheaper
Replacing the spark plugs in engines with lasers could lead to more complete fuel combustion and greener cars
After a two-year hiatus, the Large Hadron Collider will restart soon, twice as strong and with some "dark" mysteries to unlock
Global antibiotic resistance is imperilling our existence. We need clever ways to find new bug-beating drugs
If dark matter turns out to interact with photons, its glow would be visible at the edges of spiral galaxies – now we just have to find it