Fano Effect Seen Using Quantum Dot

An international team of researchers has revealed a previously unseen phenomenon known as the Fano effect by using an artificial nanostructure -- a quantum dot (QD) -- instead of an atom. The work could allow the exploration of new frontiers in quantum optics.

Observation of the Fano effect, or the interactions between a material and its surroundings, is normally prohibited by Heisenberg's uncertainty principle, which states that it is impossible to know both the exact position and the exact velocity of a subatomic-scale object at the same time.

The Fano effect changes the way an atom or molecule absorbs light or radiation, said Sasha Govorov, an Ohio University theoretical physicist on the research team.

The high-resolution laser spectroscopy experiment led by Martin Kroner and Khaled Karrai of the Center of NanoScience at the Ludwig-Maximilians University (LMU) in Munich, Germany, involved a new method. Instead of using atoms, they measured photons scattered from a single QD, or artificial atom, while increasing the laser intensity to saturate the dot's optical absorption. This allowed them to observe very weak interactions, signaled by the appearance of the Fano effect, for the first time. The quantum dots were made of indium arsenide (InAs) topped with a thin layer of gallium arsenide (GaAs).

A new theory for the new nonlinear method was developed by Govorov, who is co-author on a paper about the research published today in the journal Nature. "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."

Quantum dots, which stay in place on their own, offer research advantages over atoms, which move very fast and need to be "trapped" by laser beams for use in experiments.

The LMU team received funding from the National Science Foundation, Ohio University's Nanobiotechnology Initiative and various national organizations in Germany, the UK and the European Union.

For more information, visit: www.ohio.edu/researchnews