The goal of any tech company that joins the race to build a quantum computer is to achieve quantum supremacy. That’s the point where their design can consistently run certain algorithms faster than even the most powerful conventional supercomputers.
On Monday, Google research scientist Julian Kelly revealed a quantum processor codenamed “Bristlecone” at the annual meeting of the American Physical Society in Los Angeles. This is the chip that the company believes will achieve quantum supremacy.
This record-shattering chip contains 72 qubits, which are the quantum version of digital bits, the smallest unit of data stored on a standard computer. A bit can only have one of two values, zero or one. While qubits can be a zero, a one, or a mix of the two. This gives quantum systems the power to complete operations at preposterous speeds.
“We chose a device of this size to be able to demonstrate quantum supremacy in the future,” Kelly writes in a blog post. “We believe Bristlecone would then be a compelling proof-of-principle for building larger scale quantum computers.”
The amount of data qubits can represent grows exponentially every time one is added to a quantum processor. But sheer numbers isn’t the only thing standing in the way of quantum supremacy. Researchers have to make sure these systems of qubits have low error rates — or large circuit depth in technical terms.
Qubits are extremely unstable and can be greatly affected by noise, any disruption in their arrangement can greatly throw off results.
Kelly writes quantum supremacy can be achieved with just 49 qubits. But Google has chosen to go with a larger number to help mitigate some of this error.
“Although no one has achieved this goal yet, 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,” Kelly writes.
Of course, in order to prove that Bristlecone can do the same Google is going to have to be able to evaluate it actually works, which is another exceedingly difficult task.
Certain researchers have been able to check the work of quantum systems using artificial intelligence, but Google has made its own check. It involves looking at sample results from Bristlecone against the output from a classical computer, a process that can take a very long time.
Whether or not Google is able to achieve quantum supremacy, the simple fact that the researchers have Bristlecone in their tech arsenal means a future with quantum computing is another incremental step closer.