Two-qubit chip draws quantum computing closer

Practical entanglement and reprogrammable devices now on the horizon. Andrew Masterson reports.

Reprogrammable quantum computers are the "ultimate goal" of current research.
Reprogrammable quantum computers are the "ultimate goal" of current research.
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The ultimate goal of quantum information programming – a device capable of being reprogrammed to perform any given function – is one step closer following the design of a new generation silicon chip that can control two qubits of information simultaneously.

The invention, by a team led by Xiaogang Qiang from the Quantum Engineering Technology Labs at the University of Bristol in the UK, represents a significant step towards the development of a practical quantum computing.

In a paper published in the journal Nature Photonics, Qiang and colleagues report proof-of-concept of a fully programmable two-qubit quantum processor “enabling universal two-qubit quantum information processing in optics”.

The invention overcomes one of the primary obstacles facing the development of quantum computers. Using current technology, operations requiring just a single qubit (a unit of information that is in a superposition of simultaneous “0” and “1”) can be carried out with high precision.

However, adding a second qubit and thus enabling quantum entanglement, a critical step for quantum computing, escalates problems dramatically.

“This is recognised as one of the most challenging tasks for photonics because of the extra resources required for each entangling step,” write the researchers.

To a notable extent, the challenge has now been met. Qiang and colleagues report constructing a quantum processor capable of controlling two qubits. The new chip comprises more than 200 photonic components and utilises complementary metal-oxide-semiconductors.

The researchers report using the processor to “implement 98 different two-qubit unitary operations” at an average of 93% efficiency.

According to team member Jingbo Wang from the University of Western Australia, the results bode well for future developments in the field.

“The team have used the silicon chip to perform delicate quantum information experiments with 100,000 different reprogrammable settings,” she says.

“One of the experiments is to implement a special class of quantum walk, which allows simultaneous traversing of all possible paths in arbitrarily complex network structures.”

“Being able to explore everything at the same time offers exciting prospects for science and practical applications.”

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