Writer: Enrico Caprioglio

Editor: Karolay Lorenty

Artist: Victoria Kozlova

Quantum Supremacy – these two words were first used together by John Preskill, in 2012. He defined this concept to describe the point where quantum computers could complete tasks and solve problems that normal computers would never be able to do. Just the word quantum sounds arcane, wrapped in mystery or hidden in some other dimension parallel to ours. The word supremacy, instead, is normally used to describe the highest authority or the greatest power. He carefully chose these two words, “to emphasize that this is a privileged time in the history of our planet, when information technologies based on principles of quantum physics are ascendant”.

Google researchers claim to have reached the so-called quantum supremacy with their latest quantum processor, Sycamore, which was able to complete a task that would have taken “a state-of-the-art supercomputer” over 10,000 years. But for Sycamore, it took only 200 seconds to complete. In order to fully appreciate this milestone in information technology, let’s try to understand how a quantum computer differs from a classical computer, and look at the effect that these technological devices could have in today’s society.

A normal or “classical” computer is fundamentally made of very tiny switches called transistors. Just as a lamp can be turned on and off when current is provided or taken away, a transistor can be on or off. If it is on, we say it assumes value 1; if it is off, the value is 0. The state of a transistor (0 or 1) is the simplest form of information – we call this a bit. Multiple transistors can be combined to store more complex information or connected with each other to perform basic algebraic calculations. You might think computers are pretty stupid, and they are! Humans can compute more complex calculations; we wonder about life, love or whether we should put in milk or cereals first. However, just as we have billions of neurons in our brain, computers have billions of transistors as well. By reducing complex problems to simpler ones, we can teach computers how to solve them.

Quantum computers are fundamentally different. The smallest form of information in a quantum computer is called qubit, which can be 0 and 1 simultaneously. This might seem inconceivable, but that is what happens when we enter the quantum regime. In the quantum regime, the laws of quantum mechanics apply, which state that, before an object is observed or detected, this object is in a superposition of all its possible states. So until you observe or interfere with a qubit, the qubit is not 0, nor 1, but both at the same time! Exciting as this may sound, with only one qubit, we still have the same information we would have using one transistor (0 or 1). But what happens when we add one more qubit? A system of two qubits is simultaneously 00, 01, 10, 11 – that is four states. Thus, a normal computer would require four bits to match the same amount of states as a system of two qubits. With only 20 qubits, a quantum computer processor could potentially be in 1,048,576 states simultaneously. Google’s quantum processor had 53 working qubits, with a stunning number of nine million billions simultaneous states. The same number of kilometers you travel if you walked from the earth to the sun 60 million times!

You may now be wondering if we should start worrying about the rise of an AI quantum machine which is going to take over the world using this computational power. This scenario is quite absurd – Sycamore was required to complete a task specifically designed to demonstrate quantum supremacy. The task consisted of producing a string of nine million billion bits, for a million times and then calculate the average string produced – it probably wouldn’t be able to take over an ant colony. Moreover, qubits need to be at freezing cold temperatures and isolated from anything that could interfere with them to avoid errors in calculations, which is tremendously difficult to achieve.

Nonetheless, this is not a silly question to ask. A quantum computer could, in principle, be used to threaten cryptosecurity systems online. A normal computer would take thousands of years to break the encryption codes that safely store our bank or health details online, but more powerful quantum computers could break these codes, in the time it takes to make a cup of tea.

Fortunately, researchers foresaw this problem and organizations such as the National Institute of Standards and Technology (NIST) have been looking for potential post-quantum algorithms for encryption codes, since 2016. Earlier this year, they narrowed down 26 algorithms that could potentially be implemented in future encryption systems to be quantum-computer proof.

Quantum computers are still far from being able to be used for these kinds of purposes, but it is reassuring to know that the scientific community is not only working to build incredible machines, but also to be safe from them.