How Google's 'quantum supremacy' could unlock 'inventive' new applications

Google claims it has achieved something extraordinary, and it’s published a paper explaining how it did it.

In a paper published Wednesday in the journal Nature, researchers claim they created a quantum computing system that took 200 seconds to complete a specified task. The task would have taken a classical computer 10,000 years to complete, far longer than the lifespan of the machine, meaning Google’s setup had demonstrated “quantum supremacy.” The success of the experiment, announced ahead of the paper’s publication last month, could help pave the way for practical applications of the technology.

“I think people in Google and Silicon Valley tech companies will see that this technology may be a lot closer than they thought, and have to think about it now more carefully,” John Martinis, one of the paper’s authors, said during a press conference call Wednesday.

Sergio Boixo, another of the paper’s authors, noted in the call that a key theory in computer science is that “classical computers can efficiently emulate all realistic models of computation.” Breakthroughs like this, he explained, are “challenging one of the main tenants of classical computer science.”

It’s a big step in the drive to develop a quantum machine. A regular computer uses zeroes and ones to represent data, reflecting the “on” and “off” states in “bits.” A quantum machine adds a third state that is both on and off, creating a “qubit.” The system can theoretically take advantage of other features like entanglement, meaning it could process data much faster.

Google’s Sycamore processor is comprised of 54 qubits, but the experiment only used 53 because one was not working correctly. The experiment asked the machine to work on a random number sampling task, with numbers produced randomly by a quantum circuit. The task becomes harder as the circuit grows more complex. Sycamore took one million samples in 200 seconds, completing the task at speed.

From here, the Google team hopes to develop other applications. Martinis voiced his hope that placing a quantum computer in the cloud could encourage researchers to “be very inventive” and come up with new uses. Boixo cited several potential uses for the setup, like quantum simulations, machine learning, material sciences, and chemistry experiments.

Not everyone is on board with Google’s claim. In a blog post published Monday, IBM claimed that a computer simulating the same task could, in fact, achieve the same results in two-and-a-half days with better fidelity. This estimate, IBM claims, is a worst-case scenario. The company also argues that, even with “quantum supremacy” achieved, there will be some tasks more suited to classical computers. This makes the notion that a quantum computer has achieved superiority misleading.

Although IBM, who has also created a 53-qubit machine, claims the experiment “should not be viewed as proof that quantum computers are ‘supreme’ over classical computers,” it does admit that the experiment is “an excellent demonstration of the progress in superconducting-based quantum computing.”

The world of quantum computing may soon step into a new era.

Read the abstract below:

The promise of quantum computers is that certain computational tasks might be executed exponentially faster on a quantum processor than on a classical processor . A fundamental challenge is to build a high-fidelity processor capable of running quantum algorithms in an exponentially large computational space. Here we report the use of a processor with programmable superconducting qubits^2-7 to create quantum states on 53 qubits, corresponding to a computational state-space of dimension 2^53 (about 10^16). Measurements from repeated experiments sample the resulting probability distribution, which we verify using classical simulations. Our Sycamore processor takes about 200 seconds to sample one instance of a quantum circuit a million times—our benchmarks currently indicate that the equivalent task for a state-of-the-art classical supercomputer would take approximately 10,000 years. This dramatic increase in speed compared to all known classical algorithms is an experimental realization of quantum supremacy^8–14 for this specific computational task, heralding a much- anticipated computing paradigm.