In a feat akin to plucking a single water molecule from a vast ocean, physicists have for the first time isolated a single electron from an electronic sea. The study gives scientists a chance to learn more about the elementary particles and to employ them for quantum communication and computing devices.
The world is flush with electrons, yet they are very difficult to study individually. In metal wires and electrodes, individual electrons are virtually indistinguishable from each other because they sit together in a vast reservoir called the Fermi sea. One trick physicists have used is to strip a wire free of electrons and then inject it with particles one at a time, but those electrons don’t behave the same way they would if they were immersed in the sea. Like zoologists interested in learning the behavior of an animal, physicists want to study individual electrons in their natural environment.
In 1996, MIT physicist Leonid Levitov and colleagues proposed a way to do that. They surmised that applying a particular voltage pulse across a circuit would cause electrons within the sea to interact and produce a single electron of high energy; all the other electrons would remain in a low-energy state. The high-energy electron would glide across the surface of the Fermi sea like a lone wave in the ocean, making it easy to study.
Now, 17 years later, a European team including physicist Christian Glattli of the Saclay Nuclear Research Center near Paris has experimentally confirmed Levitov’s prediction. The researchers set up a circuit, cooled it to a few hundredths of a degree above absolute zero and sent through an electric pulse. An instrument called a beam splitter counted the electrons carried by each pulse by acting like an audio recorder on a tin roof in the rain: The hope was that it would detect the tiny splat of a single raindrop – an electron – rather than the thrashing of many drops. Sure enough, the beam splitter confirmed that each pulse triggered a lone electron to glide across the sea, the researchers report October 23 in Nature.
The study sets physicists on a path toward using electrons in quantum experiments the way they use photons, Glattli says. Photons are far easier to isolate and manipulate than electrons, so they have been the particle of choice for designing secure communication networks and rudimentary quantum computers. A new generation of quantum electronics could integrate more easily with other electronic devices.
Fittingly, Glattli and his team coined the term leviton for the single-electron pulse. “It is a terrific paper,” Levitov says. “And I say that not because [of the word] leviton.”
J. Dubois et al. Minimal-excitation states for electron quantum optics using levitons. Nature. Published online October 23, 2013. doi: 10.1038/nature12713.
A. Witze. Memories made of light. Science News. Vol. 178, July 17, 2010, p. 16.
L.S. Levitov, H.-W. Lee and G.B. Lesovik. Electron counting statistics and coherent states of electric current. Journal of Mathematical Physics. Vol. 37, October 1996, p. 4845.
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