Australian scientists invent qubit that's 10 times more stable than ever before

Australian scientists have made a breakthrough in quantum computing research by succeeding in developing a new type of quantum bit (qubit) that is able to stay in a stable superposition for 10 times longer than ever previously achieved.

Researchers from the School of Electrical Engineering & Telecommunications at the University of New South Wales (UNSW) have developed a qubit known as a "dressed quantum bit" with a record-breaking dephasing time of 2.4 milliseconds, because it consists of the spin of a single atom made from silicon that has been combined at its heart with an electromagnetic field.

The beauty of the dressed qubit is that it can retain information for far longer than an "undressed" qubit, meaning that the qubit can hold its delicate superposition long enough to perform complex calculations, as well as to enable scientists to manipulate the dressed qubit in ways that wouldn't be possible with the undressed qubit.

"We have created a new quantum bit where the spin of a single electron is merged together with a strong electromagnetic field," said Arne Laucht, a research fellow at the School of Electrical Engineering & Telecommunications at UNSW, and lead author of the paper. "This quantum bit is more versatile and more long-lived than the electron alone, and will allow us to build more reliable quantum computers."

The paper, entitled "A dressed spin qubit in silicon" is published in the journal Nature Nanotechnology.

How quantum computing works

Although currently quantum computers are merely a concept, numerous computer science researchers around the world and billions of dollars have been invested to create them, and it is believed that these new super-powerful computers will be available within the next 50 years.

While computers today are coded using a small unit of data with a single binary value of 0 or 1 called a "bit", a quantum computer would require qubits, which are in superposition so that they can have the value of 1 or 0 at the same time. This means that two qubits in superposition can be in four possible configurations at once, which would enable the quantum computer to factor huge numbers.

"The greatest hurdle in using quantum objects for computing is to preserve their delicate superpositions long enough to allow us to perform useful calculations," said Andrea Morello, leader of the research team and a programme manager in the ARC Centre for Quantum Computation & Communication Technology (CQC2T) at UNSW.

"We have now implemented a new way to encode the information: we have subjected the atom to a very strong, continuously oscillating electromagnetic field at microwave frequencies, and thus we have 'redefined' the quantum bit as the orientation of the spin with respect to the microwave field."

Race to build the first quantum integrated circuit

Since the electromagnetic field steadily oscillates at a very high frequency, any noise or disturbance at a different frequency results in a zero net effect. The researchers were able to extend the timespan during which a quantum superposition can be preserved 10 fold, and they did not need to invent a new material for the bit – it can be built using standard silicon technology.

UNSW has been researching quantum computing for a decade and previously managed to establish the most long-lived quantum bit in the solid state, by encoding quantum information in the spin of a single phosphorus atom inside a silicon chip, placed in a static magnetic field.

Australia wants to be the first in the world to develop a quantum computer in silicon, and to that end, the Australian government signed an AUS$70m ($54m, £44m) deal with UNSW in September to create a consortium to develop and commercialise a prototype 10-qubit silicon quantum integrated circuit within the next five years.