G. Fève et al., Science

Electrons in action.
An artist's conception of the single electron device.

Marching Single File Toward Qubits

The electron might have just caught up with the photon as a possible data carrier for the next generation of supercomputers. Scientists have demonstrated the ability to control a current so precisely that they can transmit electrons one at a time. More research is needed, but the achievement could someday be a key part of building a quantum computer on a chip.

In the race to create ever smaller and faster computers, quantum computing has become the ultimate goal among scientists, promising speeds and capacities far above present technologies using a tiny fraction of the power and space that conventional machines need.

The key to this new technology is quantum physics, which allows subatomic particles to exist in multiple states simultaneously and therefore perform several tasks in the same time it takes existing computers to make a single calculation. The enduring problem in attempting to create such a computer has been how to control the flow of photons or electrons carrying the information. Photons are fairly docile, but transporting them requires complex arrays of lasers, beam splitters, polarizers, and the like. Electrons require just a conductor, but they are unruly, which complicates the creation of supremely delicate quantum states.

Now, researchers have demonstrated a tiny device that can emit single electrons through a conducting medium called a two-dimensional electron gas (2DEG), every nanosecond or so. The 2DEG allows the electrons to pass undisturbed, so they can act as quantum bits, or qubits, more elaborate versions of the individual data bits in conventional computer systems. The team, at L'École Normale Supérieure in Paris, describes in today's issue of Science how they created an extremely tiny electrical insulator called a quantum dot, which allows electrons through to the 2DEG one at a time whenever it receives a tickle of electricity.

The device represents a step toward quantum computing, says physicist and co-author Christian Glattli. The next step is to begin to control the movement of qubits. Glattli says the difficulty of such control will be overcoming the signal noise generated when single electrons are emitted quickly.

Also needed is an electron detector to receive the qubits, "a challenging thing," says Stephen Giblin, a physicist at the U.K.'s National Physical Laboratory in Middlesex who wrote an accompanying Perspective in Science. Building such a detector will require a 10-fold increase in speed for single-electron detectors, he says. Nevertheless, quantum computers that use electrons are worth pursuing, he adds. Although these computers would be "messy compared to photonic systems," Giblin says, they could be fabricated easily in large numbers and would be easier to integrate with conventional electronics.

Related sites

Posted in Physics, Math