New Way to Distinguish Between Neighboring Quantum Bits: Spin

First Posted: Jun 18, 2013 02:06 PM EDT

We may be even closer to creating a large-scale quantum computer. Scientists have proposed a new way to distinguish between quantum bits, or qubits, that are placed only a few nanometers apart in a silicon chip.

Qubits are essentially the basic building blocks of quantum computers, devices that possess the capability to solve problems than even the fastest supercomputer. While conventional computing is binary, which uses the typical 1s and 0s, quantum computing relies on the fact that subatomic particles inhabit a range of states. Different relationships among these particles may coexist, and the probable states can be narrowed in order to determine an optimal outcome among a near-infinitude of possibilities. In other words, quantum computers are really, really good at picking a "best" choice.

Scientists are currently working on designing these computers, but they need to get down to the basics in order to do so. That's why they're looking at qubits. In fact, a qubit based on the spin of an individual electron bound to a phosphorous atom within a silicon chip is one of the most promising systems for building a practical quantum computer. That's mainly due to the silicon's widespread use in the microelectronics industry.

"However, to be able to couple electron-spins on single atom qubits, the qubits need to be placed with atomic precision, within just a few tens of nanometers of each other," said Michelle Simmons, leader of the research team, in a news release. "This poses a technical problem in how to make them, and an operational problem in how to control them independently when they are so close together."

Yet the researchers seem to have overcome this challenge. They were able to read-out the spins of individual electrons on a cluster of phosphorous atoms that had been placed precisely in silicon. In addition, they even developed a new method for distinguishing between neighboring qubits that were only a few nanometers apart.

"If each electron is hosted by a different number of phosphorous atoms, then the qubits will respond to different electromagnetic fields-and each qubit can be distinguished from the others around it," said Holger Buch, lead author of the study, in a news release.

The new techniques reveal that it's possible to maintain long spin lifetimes of electrons on multi-donor systems. It now only offers a new method for addressing individual qubits, but also paves the way for a future large-scale quantum computer. This finding could be huge for developing a computer that could perform calculations at speeds that were before unheard of.

The findings are published in the journal Nature Communications.

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