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Quantum processor demonstrated under less frigid conditions

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Scientists have demonstrated a basic silicon-based quantum processor which functions at temperatures a magnitude higher than the basic quantum computers being developed by key players like Google and IBM.

Quantum computers are in early stages of development, but have the potential to completely outperform classical computers. They use qubits as their basic units of information, which can exist in a superposition of binary states (rather than just as a 0 or 1 like a bit).

There are a number of serious technical barriers in quantum computing, such as the fact that each pair of qubits added to a system in close proximity with other qubits increases thermal energy, increasing risk of errors. This means that quantum computers only work when the qubits are spaced out and cooled to a fraction of a degree above absolute zero.

This makes them impractical, given how expensive and energy-intensive dilution refrigeration can become close to absolute zero. It can cost millions of pounds to maintain systems at these temperatures to perform calculations, which – until recently, when Google claimed to have reached “quantum supremacy” – can also be performed on classical computers.

Now, scientists have demonstrated a quantum processor unit cell which works at 1.5K (-271.65°C). Despite still being much colder than anything we are familiar with in our everyday lives, this represents quantum computing at temperatures approximately 15 times higher than had previously been achieved by IBM and Google, who use superconducting qubits cooled to almost absolute zero.

According to the University of New South Wales’ Professor Andrew Dzurak, who led one of the research groups: “This is still very cold, but is a temperature that can be achieved using just a few thousand dollars’ worth of refrigeration, rather than then millions of dollars needed to cool chips to 0.1K. While difficult to appreciate using our everyday concepts of temperature, this increase is extreme in the quantum world.

“Our new results open a path from experimental devices to affordable quantum computers for real-world business and government applications,” said Dzurak. According to the researchers, as temperatures rise above 1K, the cost of maintaining quantum computing systems drops “substantially” and efficiency improves.

Dzurak’s team – which worked with collaborators in Canada, Finland and Japan – first revealed their experimental results in February last year, which was followed months later by a Dutch group confirming similar results. Dzurak and his team have now detailed their work in a Nature paper. The paper was published back-to-back with the Dutch group’s paper, which demonstrated a quantum circuit which operates at 1.1K.

The basic quantum processor developed by Dzurak’s team comprises of two qubits confined in a pair of quantum dots (tiny semiconductor particles) embedded in silicon. While previously qubits have been separated in order to prevent heating, and connected with cables to read information, this team has instead used electrons tunnelling between quantum dots – which can be placed close together – to “read” the qubits.

At this stage, the researchers have demonstrated that the system maintains coherence 1.5K for two microseconds: approximately as long as more conventional 0.1K quantum processor can maintain coherence.

According to the researchers, a scaled-up version of the unit cell could be manufactured using conventional manufacturing processes and equipment, operate without the need for million-dollar-refrigeration, and would be easier to integrate with conventional hardware due to the use of a silicon-based platform.

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