Spin control quantum computing needs

Australian engineers are claiming a breakthrough in quantum computing, having increased the length of the “superposition” of quantum bits vital for making calculations.

“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, lead author of the paper published in Nature Nanotechnology.

“This quantum bit is more versatile and more long-lived than the electron alone, and will allow us to build more reliable quantum computers.”

Scientists hope the quantum computers will become revolutionary tools for solving certain sorts of problems, including the the design of complex drugs and advanced materials, minimising lengthy trial and error testing.

Traditional computing relies on a transistor being on or off to provide inputs of the 1s and 0s of the binary code the computer uses to process instructions.

Quantum computing instead works on the basis of the quantum bit, or qubit, being spin-up, spin-down or in a “superposition” of both: 1 and 0 at the same time.

Theoretically, this should enable a quantum computer to weigh multiple solutions to a complex problem at once, and solve it at phenomenal speed.

The new quantum bit remains in a stable superposition for 10 times longer than previously achieved, the study says.

It is made up of the spin of a single atom in silicon and merged with an electromagnetic field – known as “dressed qubit”.

“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.

“Our decade-long research program had already established 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,” he said.

What Laucht and colleagues did was push this further.

“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.”

Morello says the “dressed qubit” can be controlled in a variety of ways that would be impractical with an “undressed qubit”.

“For example, it can be controlled by simply modulating the frequency of the microwave field, just like in an FM radio.”

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