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Has Google Actually Achieved Quantum Supremacy? Why IBM Doesn’t Think So

November 8, 2019

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Google recently announced they achieved quantum supremacy, an extremely important milestone in the development of quantum computers. Shortly after, IBM decided to spoil the party by announcing that quantum supremacy had not actually been achieved. Who’s right and who’s wrong? Can both tech giants be right and wrong at the same time? Maybe.

Let’s Start from The Beginning: What Is a Quantum Computer

A quantum computer can potentially reduce execution time to minutes or hours for problems that would previously have taken hundreds of years to solve on humanity’s best supercomputers. Instead of regular bits, which are always either 0 or 1, a quantum computer uses qubits or the quantum analog of bits.

A qubit is a two-state quantum-mechanical system. In a classical system, a bit would have to be in one state or the other. However, quantum mechanics allows the qubit to be in a superposition of both states at the same time, a property that is fundamental to quantum computing.

According to researchers, finance, medicine, chemistry, and artificial intelligence are all expected to be transformed by quantum computing.

Google claims to have just achieved Quantum Supremacy. IBM: “Not so fast”

Google has recently announced a major breakthrough at its California research lab, a milestone that scientists have been working toward since the 1980s: quantum supremacy. According to the tech giant, its researchers had performed a calculation that the largest supercomputers could not complete any sooner than 10,000 years. And they had done it in 3 minutes and 20 seconds.

“We developed a new 54-qubit processor, named Sycamore, that is comprised of fast, high-fidelity quantum logic gates, in order to perform the benchmark testing. Our machine performed the target computation in 200 seconds, and from measurements in our experiment we determined that it would take the world’s fastest supercomputer 10,000 years to produce a similar output”, according to the blog post. Google claims the Sycamore quantum computer is fully programmable and can run general-purpose quantum algorithms. The team is already working on near-term applications, including quantum physics simulation and quantum chemistry, as well as new applications in generative machine learning, among other areas.

While scientists all over the world cheered Google’s achievement, IBM rapidly spoiled the party saying those results aren’t quite as groundbreaking as they may seem. The rival company acknowledges the impressiveness of the Sycamore system but has far more faith in the abilities of classical supercomputers to keep up.

IBM rapidly reacted and disputed Google’s assertion in a blog post: “Recent advances in quantum computing have resulted in two 53-qubit processors: one from our group in IBM and a device described by Google in a paper published in the journal Nature. In the paper, it is argued that their device reached “quantum supremacy” and that “a state-of-the-art supercomputer would require approximately 10,000 years to perform the equivalent task.” We argue that an ideal simulation of the same task can be performed on a classical system in 2.5 days and with far greater fidelity. This is, in fact, a conservative, worst-case estimate, and we expect that with additional refinements the classical cost of the simulation can be further reduced”

Quantum Supremacy – When a Simple Definition Sparks a Huge Debate

How did we end up in a situation where Google and IBM are contradicting each other over quantum supremacy? As always, the devil is in the details. Basically, the essence of the disagreement between the two tech giants is related to the apparently simple definition of Quantum Supremacy. Coined in 2012 by John Preskill, a theoretical physicist at the California Institute of Technology, the definition of Quantum Supremacy describes the exact moment when a quantum computer surpasses even the best supercomputers in the world. While the term caught on, scientists came to hold different ideas about what it means. 

Today, most experts interpret the notion as the moment a quantum computer performs a calculation that, for all practical purposes, a classical computer cannot. This is where the pieces of the puzzle no longer fit for Google: “practical” is a vague concept. In the paper published in Nature magazine, Google claims that its Sycamore processor took 200 seconds to perform a calculation that the world’s best supercomputer would need 10,000 years to perform. IBM argues that its Summit machine, which fills an area the size of two basketball courts, could perform the calculation in two and a half days with far greater fidelity and with additional refinements.

For some, Google’s announcement looks like a PR exercise. For others, like IBM for example, the approach is like comparing apples with oranges, forgetting that classical supercomputers have advantages. After the recent breakthroughs in quantum computing, one thing is sure: the race is only starting to heat up.