Scientists discover new method of observing interactions in nanoscale systems

Scientists have used new optical technologies to observe interactions in nanoscale systems that Heisenberg's uncertainty principle usually would prohibit, according to a study published recently in the journal Nature.

Researchers conducted experiments with high-powered lasers and quantum dots - artificial atoms that could be the building blocks of nanoscale devices for quantum communication and computing - to learn more about physics at the nanoscale.

One common phenomenon in physics is the Fano effect, which occurs when a discrete quantum state - an atom or a molecule - interacts with a continuum state of the vacuum or the host material surrounding it. The Fano effect changes the way an atom or molecule absorbs light or radiation, said Sasha Govorov, an Ohio University theoretical physicist who is co-author on the paper.

In experiments on nanoscale systems, Heisenberg's uncertainty principle sometimes blocks scientists from observing the Fano effect, Govorov explained. The interaction of the nanoscale system and its continuum state surroundings can't be detected.

But in a new high-resolution laser spectroscopy experiment led by M. Kroner and K. Karrai of the Centre of NanoScience at the Ludwig-Maximilians University in Munich, Germany, scientists utilised a new method. They measured photons scattered from a single quantum dot while increasing the laser intensity to saturate the dot's optical absorption. This allowed them to observe very weak interactions, signalled by the appearance of the Fano effect, for the first time.

A theory for the new nonlinear method was developed by Govorov. 'Our theory suggests that the nonlinear Fano effect and the method associated with it can be potentially applied to a variety of physical systems to reveal weak interactions,' he said.

Scientists also can revisit older experiments on atoms by using modern tools such as highly coherent light sources that are strong enough to reveal such nonlinear Fano-effects, Karrai said. 'We can explore new frontiers in quantum optics,' he noted.

The researchers were funded by the National Science Foundation (USA), SFB 631 (Germany), A. von Humboldt Foundation (Germany), Engineering and Physical Sciences Research Council (UK), SANDiE (EU), Royal Society of Edinburgh, German Excellence Initiative via the Nanosystems Initiative Munich (NIM), and Ohio University's Nanobiotechnology Initiative.

Other co-authors on the study were S. Remi, B. Biedermann, S. Seidl and of the Ludwig-Maximilians University, W. Zhang of Ohio University; A. Badolato and P.M. Petroff of the University of California at Santa Barbara; and R. Barbour, B.D. Gerardot and R.J. Warburton of the Heriot-Watt University in Edinburgh, Scotland.