In the Race for Quantum Supremacy, Researchers Claim to Pull Ahead of Google

In many respects, the quantum computing field is still in its infancy. In 2019, Google showed the feasibility of quantum computing for the first time, claiming "quantum supremacy"—a term that refers to the ability of a programmable quantum device to solve a problem that no classical computer can solve within a feasible amount of time. 

 

Rendering of Google's Sycamore processor. Image (modified) used courtesy of Google

 

Now, a group of researchers from the Chinese Academy of Sciences says they have usurped Google's claims in a newly released study.  

 

First, What is Quantum Supremacy?

Much of the hype around quantum computing comes from the theoretical projections of how quantum computing will eventually perform. In practice, however, researchers are far from reaching this potential outside of a temperature-controlled lab. 

Quantum supremacy is the ability of a quantum computer to outperform a classical computer in any given task.  Computer scientists confirm quantum supremacy based on two factors: first, they must show that a classical computer could not have solved a certain calculation within a reasonable timeframe, and second, they must prove that a quantum computer can perform the calculation quickly.

 

Google's Quantum Computer Kicks Off the Race

By these standards, Google achieved quantum supremacy for the first time in 2019 when its quantum computer Sycamore outperformed even the world’s best supercomputer at a given task.

Sycamore was tasked with simulating the performance of a quantum computer (a very self-referential goal), in which a random quantum circuit was generated to produce a finite-length bitstring. Because of the effects of quantum interference, certain bitstrings have a higher likelihood of occurring than others, and finding which of these bitstrings is most likely becomes exponentially more difficult as the number of qubits and gate cycles increases.

 

Sycamore performed a task in 200 seconds that would have taken a classical computer 10,000 years to complete. Image used courtesy of Google

 

In the experiment, Google showed that at 53 qubits and a depth of 20 gate cycles, its Sycamore quantum computer completed the task in 200 seconds while the world’s fastest classical computer would have taken 10,000 years. Sycamore's ability to solve this problem so much faster than a classical computer marked a major milestone in the quantum computing field, breathing life into the idea that quantum computing might truly be a feasible pursuit. 

 

New Research Challenges Google’s Claims

Researchers at the Chinese Academy of Sciences now claim to trump Google's 2019 assertion of quantum supremacy. 

When calculating the 10,000-year figure for a classical computer, Google researchers assumed the computer would run the Schrodinger-Feynman algorithm. The researchers at the Chinese Academy of Sciences decided to develop a new, more efficient algorithm to perform this task at a faster rate.

 

Representation of the 3D network algorithm used by the researchers. Image used courtesy of Pan et al

 

The group's new algorithm ran Google’s 2019 quantum supremacy task by organizing the problem as a 3D network of tensors, each consisting of its own set of interconnected vectors. Using the new algorithm on a computing engine consisting of 512 GPUs, the researchers completed the task in 15 hours compared to the 10,000 hours estimated by Google. 

The researchers posit that if this algorithm were run on the world’s fastest supercomputers, the total time for computation could be on the order of seconds—making it faster than Sycamore’s performance.

 

The Race for Quantum Supremacy Continues

Responding to this new research, Google's principal scientist for Google Quantum AI Sergio Boixo said, “In our 2019 paper, we said that classical algorithms would improve...We don’t think this classical approach can keep up with quantum circuits in 2022 and beyond.”

While Google may have been the first to start the race for quantum supremacy, it certainly didn't end it. Pan Zhang, one of the researchers involved in the Chinese Academy of Sciences study, asserts that in the future, researchers need to find real-world demonstrations to prove a quantum advantage.