Google Chip Takes Aim At ‘Quantum Supremacy’

Google's latest quantum processor, Bristlecone. Google

The ‘Bristlecone’ quantum chip may become the first to demonstrate quantum systems’ theoretical performance edge over conventional supercomputers

Google has said its new quantum processor, ‘Bristlecone’, could help it become the first company to demonstrate the use of quantum computing to solve problems faster than a conventional supercomputer.

That feature, which has remained theoretical to date, but which is the primary draw of quantum technologies, is known as ‘quantum supremacy’.

In theory, quantum computers – built of ‘qubits’ that are able to hold more than one state at a time – offer performance so much greater than that of today’s supercomputers that they can make new applications practical for the first time.

At the annual meeting of the American Physical Society in Los Angeles, where it presented the chip, Google said Bristlecone aims to build on a key achievement of its predecessor – low error rates.

A Bristlecone chip being installed by Research Scientist Marissa Giustina at the Quantum AI Lab in Santa Barbara. Credit: Google

Low error rates

Current qubits are highly unstable and as such must run at ultra-low temperatures to prevent errors from creeping in.

A previous nine-qubit linear array demonstrated low error rates for readout, single-qubit gates and two-qubit gates.

Bristlecone uses the same scheme for coupling, control and readout, but is scaled to a square array of 72 qubits, Google said.

It plans to use the chip to conduct research into first and second-order error-correction and facilitate quantum algorithm development on working hardware.

It has developed a benchmarking tool for measuring error rates and said it wants to check Bristlecone’s output against a simulation running on a conventional system.

“If a quantum processor can be operated with low enough error, it would be able to outperform a classical supercomputer on a well-defined computer science problem,” Google said in a prepared statement. “We calculate quantum supremacy can be comfortably demonstrated with 49 qubits, a circuit depth exceeding 40, and a two-qubit error below 0.5 percent.”

Intel’s 48-qubit test chip. Credit: Intel

‘Cautious optimism’

If Bristlecone’s 72 qubits can achieve similar error performance rates to the 9-qubit device, it would be a compelling proof-of-principle for building larger-scale quantum computers, Google said.

“We are cautiously optimistic that quantum supremacy can be achieved with Bristlecone,” the company stated.

Microsoft, Intel, IBM and an array of startups and academic laboratories are all working on quantum computers using widely varied approaches.

IBM has a 50-qubit computer running in its labs and last year began offering a 20-qubit system via the cloud for researchers to experiment with, an upgrade from a five-qubit cloud computer launched earlier in the year.

Alibaba said earlier this week it would begin offering access to an 11-qubit system of its own online. The system was built in collaboration with the Chinese Academy of Sciences (CAS) and runs at temperatures as low as 10 milli-Kelvin, or -273° C.

In September Microsoft announced the Q# quantum programming language and a quantum API for developers, acknowledging they were aimed at future systems that might not come into being for a decade or more.

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