Google takes step forward at quantum supremacy with 72-qubit chip

LOS ANGELES - Google takes a step forward in its bid to become the first company to demonstrate "quantum supremacy" with its newest 72-qubit quantum processor, which was unveiled this week at annual American Physical Society meeting here.

The chip, known as Bristlecone, is an expanded version of their previous 9-qubit linear quantum processor. Google believes that Bristlecone will be the chip that helps the internet giant to become the first company to demonstrate quantum supremacy.

"We are cautiously optimistic that quantum supremacy can be achieved with Bristlecone," Julian Kelly, a research scientist at Google's Quantum AI Lab wrote on Monday in a blog post, "and feel that learning to build and operate devices at this level of performance is an exciting challenge."

Quantum supremacy is the potential ability of quantum computing devices to solve problems that classical computers practically cannot.

"We believe the experimental demonstration of a quantum processor outperforming a supercomputer would be a watershed moment for our field, and remains one of our key objectives," said Google's blog post.

The general assumption in the industry is that it will take 49 or 50 quantum bits, or qubits, to achieve quantum supremacy, the capability of a quantum computer to outperform the largest supercomputers on certain computational tasks, a 72-qubit processor should be more than enough to achieve such a milestone.

However, a quantum computer requires not only a large number of qubits. Crucially, the error rates on readout and logical operations of such a system must be low enough for it to be of practical use.

The device uses the same scheme for coupling, control, and readout, according to Kelly. But instead of using a linear array design, it is scaled to a square array of 72 qubits. The guiding design principle for this device is to demonstrate similar error rates they were able to achieve on the 9-qubit hardware: 1 percent for readout, 0.1 percent for single-qubit gates, and 0.6 percent for two-qubit gates.

"Operating a device such as Bristlecone at low system error requires harmony between a full stack of technology ranging from software and control electronics to the processor itself," writes the team. "Getting this right requires careful systems engineering over several iterations."

There are other players in the game, too.

In January, Intel announced its own 49-qubit quantum chip. Last November, IBM announced that it was testing a prototype quantum processor with 50 qubits.

IBM's qubits look a lot like Google's, but Microsoft, Intel, and startups like IonQ are pursuing vastly different qubit architectures.

In China, scientists have made remarkable progress in quantum science and technology over the past year, leaping to a world-leading position in the field of quantum communications.

China has also made a breakthrough in quantum computing. Also in 2017, Chinese scientists have built world's first quantum computing machine that goes beyond the early classical - or conventional - computers, paving the way to the ultimate realization of quantum computing beating classical computers.

Chinese scientists are exploring three technical routes: systems based on single photons, ultra-cold atoms and superconducting circuits.

There are also many other groups around the world pursuing different approaches to achieve the "supremacy."