Quantum Computing Gets A Leap Forward With New Qubit Spin Control Technique

Quantum computing has been hailed as the next big leap forward in processing power, and a group of University of New South Wales (UNSW) researchers may have just solved one of its fundamental problems.

The team of researchers figured out a way to precisely align the necessary phosphorous atoms for quatum bits, or qubits, to be effectively utilized.

What are qubits, you say? And what's phosphorous got to do with it?

Qubits are the basic buildings blocks of quantum computing. Rather than storing information in 0s or 1s like our current-day binary chips do, quantum computers store information in an electron's spin. The electron can be spinning up, or down, or any combination of the two, allowing for an exponential increase in computing power. The problem is, one of the most effective qubit technologies requires the electron to be bound to phosphorous atoms laid incredibly close to each other on silicon chips.

"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 professor Michelle Simmons, leader of the research team.

"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 operational problem is simple: affecting the spin of one qubit can affect the spins of others. 

"It is a daunting challenge to rotate the spin of each qubit individually," says lead author of the study detailing the findings Holger Büch.

"If each electron spin-qubit is hosted by a single phosphorus atom, every time you try to rotate one qubit, all the neighbouring qubits will rotate at the same time - and quantum computation will not work. 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 explained.

The UNSW was able to circumvent the issue by designing a manufacturing process utilizing scanning tunneling microscope that deposited a precise layer of hydrogen that was then used to fuse phosphorous atoms exactly the way they wanted to into the silicon.

"This is an elegant and satisfying piece of work," says Professor Simmons, Büch's PhD supervisor. "This first demonstration that we can maintain long spin lifetimes of electrons on multi-donor systems is very powerful. It offers a new method for addressing individual qubits, putting us one step closer to realizing a practical, large-scale quantum computer."

You can read the full publishing findings in the journal Nature.