An international team of researchers from ETH Zurich, Princeton University and LMU Munich have used lasers to peek into the complex relationship between a single electron and its environment, a breakthrough that could aid the development of quantum computers.

The research brings fresh insight 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, but that was not the case with these metals.

The researchers investigated the use of a laser to probe electrons evolving into the Kondo state. They first developed a theory about how laser light scattered off electrons could carry information about this process. Depending on the state of the electron, they surmised, it should absorb different 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.

To isolate the electrons, used nanostructured devices, small machines built one atom at a time that trap the electrons in small wells. The particles are only provided limited isolation in the wells and so eventually become entangled with a cloud of surrounding electrons in the device.

The researchers tested the idea by projecting a laser beam on the device and measuring the light that was transmitted. The light signature matched theoretical predictions.

Ref.: H. E. Türeci, A. Imamoglu, et al., Quantum quench of Kondo correlations in optical absorption, Nature, 2011; 474 (7353): 627 [DOI: 10.1038/nature10204]