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  • Revealed: The private lives of electrons

Photonics Spectra
Sep 2011
Compiled by Photonics Spectra staff

PRINCETON, N.J. – Using laser light, scientists have looked into the complex relationship that develops between a single electron and its environment, known as a Kondo state. The break-through could aid the development of quantum computers.

Scientists at Princeton University have brought fresh ideas to the study of the Kondo problem, a phenomenon first observed in the 1930s when researchers were surprised to find that resistance to electricity flowing through certain metals increases at very low temperatures. Normally, resistance through metals decreases as temperature is lowered.

A tangled relationship

Thirty years later, Japanese scientist Jun Kondo explained the phenomenon as resulting from the presence of cobalt or other magnetic impurities in the metals. Other scientists further realized that the Kondo effect resulted from a relationship between electrons known as entanglement, in which the quantum state of one electron is tied to the quantum states of neighboring electrons, even if the particles are later separated by considerable distances. In the case of the Kondo effect, a trapped electron is entangled in a complex manner with a cloud of surrounding electrons.

Intrigued by this effect, researchers set out to understand how a trapped electron becomes entangled with its environment. They hoped the findings could help overcome barriers to quantum computing.

Although previous observation methods allowed scientists to make measurements of the Kondo state, they could not provide information on how electrons developed such a relationship with their surroundings. To better understand how electrons become entangled, an international team of scientists from the US, Germany and Switzerland investigated the idea using a laser to probe electrons that evolve into the Kondo state. The investigators developed a theory about how laser light scattered off electrons could carry information about this process.

They discovered that, depending upon the state of the electron, it should absorb various colors of laser light to varying degrees. The light reflected back would carry a signature of the entangled quantum state, offering a window into the relationship between the trapped electron and its environment. They used nanostructured devices to isolate the electrons and tested their theory by projecting a laser beam on the device and measuring the transmitted light.

The light signature matched theoretical predictions, and the researchers discovered that they could use it to confirm when they had turned off the Kondo state using a magnetic field.

The findings, which appeared in Nature (doi: 10.1038/nature10204), could allow new ways of storing and processing information or threaten to destabilize the computing process.

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