What Does Google’s Quantum Supremacy Achievement Mean?

Spoiler: You Don’t Need to Upgrade Your Desktop Anytime Soon

Photograph of Google’s Sycamore quantum processor by Erik Lucero

On October 23, Google published a paper in the scientific journal Nature and an article demonstrating the ability of its Sycamore quantum processor to perform a target computation in 200 seconds. Why is that a big deal? In comparison, Google claims that the world’s fastest supercomputer would take 10,000 years (!) to perform this same computation. The ability of a quantum computer to perform a task that is practically impossible with a traditional computer is quantum supremacy. Google, working with NASA and Oak Ridge National Laboratory, became the first company to make this breakthrough.

But what is Quantum Computing?

Everything you do on a computer is ultimately converted to 0s and 1s and is represented in bits where each bit can either be a 0 or 1. In a quantum computer, this fundamental aspect changes. A quantum computer uses quantum bits or qubits which can represent both 0 and 1 simultaneously. A quantum computer is able to do this by applying key concepts from quantum mechanics: superimposition and entanglement.

Superimposition is the phenomenon that allows quantum computers to simultaneously be in multiple states (both 0 and 1). In a classical computer, for example, 2 bits can store one state out of 2² (=4) choices, whereas in a quantum computer with 2 qubits, all 2² (=4) states can be represented at the same time because of superimposition. Only when the qubit is finally measured to check for the result of a calculation, it collapses to either 1 or 0. This is not unlike a coin spinning in the air before landing. The Sycamore chip developed by Google uses a 53 qubit processor, which is capable of holding 2⁵³ states simultaneously. Theoretically, a 100 qubit quantum computer would be more powerful than all the supercomputers on the planet combined.

Entanglement is the other important feature that differentiates quantum from classical. This phenomenon allows pairs of quantum bits to be interconnected in a way that a change in the state of one will affect the state of the other. This applies even if the two qubits are quite far from each other, even as apart as the two ends of the universe, leading Einstein to famously describe it as “spooky action at a distance.”

Superimposition and entanglement make quantum computing dramatically and exponentially faster than traditional machines. Whereas in a traditional machine, doubling the number of bits doubles the processing power, in a quantum computer, doubling the number of qubits results in an exponential increase in processing power. A simple analogy to drive home this concept is to look at how both the computers find the right path through a maze. A classical machine tries every path one by one until it comes across the right path that allows it to escape the maze. A quantum computer tries all paths at the same time and provides the right path instantaneously.

But the biggest barrier to quantum computing, which is the main reason why we haven’t seen any quantum computer be practically applied to solve real-world problems, is decoherence.

The quantum superimposition state is extremely fragile. At any moment, disturbances (or noises) such as slight changes in vibration or temperature can result in the interference and breakdown of quantum behavior. This is known as decoherence. This is why quantum processors are built inside environment controlled, super-cooled rooms. But these controlled measures do not eliminate the chance of error, and this is why, even with Google’s new Sycamore processor, we are still in the NISQ (Noisy Intermediate-Scale Quantum) era. Once quantum processors are advanced enough, then we enter an era where these computers are said to be fault-tolerant.

A video explainer on how quantum computers work:

What does quantum computing allow us to do?

The first adopters of this technology will be governmental agencies, universities and research and development companies who will use it to solve problems in fields that current technology just doesn’t allow. Richard Feynman proposed one such field in 1981: quantum mechanics.

In an interview Google CEO Sundar Pichai gave after the paper was published, he highlighted the importance of Google’s achievement saying that “the real excitement about quantum is that the universe fundamentally works in a quantum way, so you will be able to understand nature better.” Scientists can use quantum computers to model different simulations, combinations and solutions to come up with a better understanding of how the world works. Some possibilities on the horizon are new drug discoveries, better weather predictability, efficient fertilizer production, building better batteries, supporting advanced space missions, more advanced machine learning capabilities, and advanced AI.

Another field of interest, as well as concern, is cryptography. The state-of-the-art technology to secure private information like credit card details and passwords use factorization to secure data because even the world’s fastest supercomputers would take hundreds of years to prime factorize a number. But in 1904, Peter Shor developed an algorithm to crack this code. However, he needed a quantum computer to run his algorithm. Within a decade or two, quantum computers will be capable of running Shor’s algorithm and make existing encryption technologies obsolete but also introduce the possibility of new and more secure cryptography.

In reality, we do not know what quantum computing has in store for us until it becomes more accessible. There are so many opportunities that we just cannot predict yet and as Google expressed in the last line of their paper: “We are only one creative algorithm away from valuable near-term applications.”

So has Google heralded us into a new world of possibilities?

Yes and No.

First, IBM published a response claiming the task performed by the quantum processor can be done on an IBM Summit supercomputer in 2.5 days, a worst-case estimate, challenging the “10,000 years” claim made by Google. If true, it means that a classical computer can perform the task in a reasonable amount of time, dismissing Google’s claim of quantum supremacy. Quantum supremacy as defined earlier is when a quantum computer performs a task which is practically impossible to do on a classical computer. Google has challenged IBM to run the same calculations and submit proof for its claim. IBM also expressed concerns about the term quantum supremacy which is misleading because it implies that classical computers are inferior, when, in reality, quantum computers and classical computers will work side by side because each has its unique advantages.

The second argument is that Google’s achievement is limited to specific tasks. Google programmed the quantum processor to run a task involving the use of random numbers which was not practically possible on a classical machine. While Google claims the computer is fully programmable to run general-purpose quantum algorithms, it doesn’t mean it can perform all tasks that a classical computer can do. Neither is Google claiming that their processor can be used for real-world applications. It was rather developed to reach an important milestone and open up the gates for future research.

Google isn’t the only company working towards advancing the quantum computer. In fact, companies like IBM and D-Wave Systems already have quantum computers that are accessible to researchers through the cloud and allows users to perform various tasks. But none of these machines have shown quantum supremacy yet. Google claims to have achieved that feat in a narrow application. Google’s CEO Sundar Pichai compares this feat to the first flight by the Wright Brothers in 1903. It wasn’t the first object to fly and it only flew for 12 seconds, having no practical application, but it showed the world a self-propelled aircraft heavier than air can fly. It led to the current day airplane. Google’s Sycamore processor is like the Wright Flyer. It shows us what is possible with quantum computers but we still have a long way to go before such computers can be used meaningfully and effectively to solve real-world problems.