New step towards silicon based quantum computer

Researchers at the University of New South Wales have proposed a new way to distinguish between quantum bits that are placed only a few nanometers apart in a silicon chip, taking them a step closer to the construction of a large-scale quantum computer.
Quantum bits, or qubits, are the basic building blocks of quantum computers — ultra-powerful devices that will offer enormous advantages for solving complex problems.
Professor Michelle Simmons, leader of the research team, said a qubit based on the spin of an individual electron bound to a phosphorus atom within a silicon chip is one of the most promising systems for building a practical quantum computer, due to 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,” she says.
“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.”
The UNSW team, in collaboration with theorists at Sandia National Laboratories in New Mexico, has found a solution to both these problems. Their study is published in the journal Nature Communications.
In a significant feat of atomic engineering, they were able to read-out the spins of individual electrons on a cluster of phosphorus atoms that had been placed precisely in silicon. They also propose a new method for distinguishing between neighboring qubits that are only a few nanometers apart.
“It is a daunting challenge to rotate the spin of each qubit individually,” says Holger Büch, lead author of the new study.
“But if each electron is hosted by a different number of phosphorus atoms, then the qubits will respond to different electromagnetic fields — and each qubit can be distinguished from the others around it,” he says.
“This is an elegant and satisfying piece of work,” says Professor Simmons, center director and Mr Büch’s PhD supervisor.