One quantum problem solved; many more to go

World-first demonstration of successfully controlled qubit coupling achieved

Researchers in Japan have developed new circuit technology touted to be the vital next step towards the realisation of a practical quantum computer.

A collaborative effort between Japan Science and Technology Agency (JST), the Institute of Physical and Chemical Research (RIKEN), and electronics vendor NEC Corporation, the technology is said to be the world's first quantum bit (qubit) circuit that can control the strength of coupling between qubits.

Current electronics rely on the manipulation of binary bits between two states - on and off, or one and zero - to store information. In quantum computing, information is stored in qubits, which can exist in a much larger range of states.

While previous advances have been made in establishing qubits and quantum logic gates, the coupling of qubits so far has been difficult to control.

"It has hitherto been difficult to switch the movement of one bit and two bits in the same quantum bit, although the bit's movements in the state of one single bit and the coupling of two bits have been confirmed," explained researcher Jaw-Shen Tsai of NEC.

The new technology enables the coupling of qubits to be controlled by employing an additional qubit in between the coupled qubit pair. The additional qubit acts as a non-linear transformer that is able to turn on and off the magnetic coupling between the two coupled qubits.

Using the new scheme, researchers have successfully employed a coupled two-qubit system to carry out a multi-quantum control experiment involving the turning on and off of the coupling.

Quantum computing is expected to be a vast improvement on today's most modern supercomputers due to its potentials of performing functions exponentially faster than any classical computer.

Having been employed at NEC for the past 24 years, Tsai anticipates quantum computing to continue to have a significant role in NEC's research and development efforts.

"NEC has been supporting this project for the past 10 years," he said. "One of the main businesses of NEC's is information processing, so naturally I would think the top management would support such a revolution of information processing, and I'm not surprised that they are supporting this project."

But there is still a long way to go before quantum computing becomes a reality, Tsai said. With ongoing improvements in conventional computers and their applications, Tsai expects the development of a practical quantum computer to be more than ten years away.

Meanwhile, the researchers are making plans for more complicated quantum computation that involve more computation steps and more qubits, in order to create a more realistic system and keep abreast of competition from other laboratories in the U.S. and Europe.

"In this particular technology, we have achieved a lot in the past. But many other labs are developing fast, so competition is there and we hope we can keep producing things, like what we have just disclosed, in the future," Tsai said.

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