In 2012, theoretical physicist John Preskill came up with a formulation of quantum supremacy, the superiority of quantum computers. He named it the moment when quantum computers can do things that are not possible for ordinary computers.

Seven years later, in autumn 2019, Googles quantum computer Sycamore reached this milestone. In 200 seconds, the machine performed a mathematically designed calculation so complex that it would take the world’s most powerful supercomputer, IBM’s Summit, 10,000 years to do it. This makes Google’s quantum computer about 158 million times faster than the world’s fastest supercomputer.

The quantum computer uses the rules of quantum mechanics to perform calculations beyond human comprehension. Quantum mechanics is a branch of physics that deals with photons, electrons and atomic nuclei.

These smallest building blocks of the universe behave completely illogically. For example, the states of two particles can be connected, even though they are a long way apart, and one particle can be in two places at the same time.

By mimicking the complex chemical and physical processes of nature at the atomic level, the quantum computer can help develop new medicines and invent superconducting materials that conduct electricity without loss of energy, for example.

But to start a new scientific golden age, the researchers behind the new technology still have a few hurdles to overcome.

The computing power of the quantum computer comes from so-called quantum bits, abbreviated to qubits. On an ordinary computer, data is stored as bits with a value of 0 or 1. Four classical bits can together create 16 different data combinations — (0000, 0001, 0010, etc.) — but the classical computer can only work with one of these combinations at a time.

Qubits can have both values, 0 and 1, at the same time. In this state, called superposition, the computer can work with all 16 combinations of data at the same time. For each added qubit, computing power increases exponentially. According to the researchers, a quantum computer with 300 qubits can perform more calculations simultaneously than there are atoms in the universe.

The 0 and 1 come from the binary number system on which computers base their calculations since they were so big that they filled a living room and worked with radio tubes instead of transistors.

But for the binary numbers to work on a computer, there must be something physical that can do it. And that is the computer’s microchip: in it, millions of tiny transistors switch the current on the microchip on or off. The more transistors the microchip contains, the more information the computer can process simultaneously.

Google’s quantum computer, Sycamore, and IBM’s, IBM Q System One, also process data using microchips. Instead of millions of transistors spitting out zeros and ones, the quantum computer’s brain’ contains very few qubits. The Sycamore chip has 53, and the IBM Q System One 20.

The qubits are made of the element niobium and pressed into a chip of silicon, the material that ordinary computer chips are made of.

By separating two niobium electrodes with a thin layer of aluminium oxide, a so-called Josephson contact is created, through which a quantum mechanical superposition can occur. A Josephson contact is only possible if the material is superconducting, meaning that it has no electrical resistance.

This is the biggest challenge to overcome when developing quantum computers for the home and office.

Because the properties of quantum mechanics occur only at the tiniest scale, the slightest disturbance in the calculations is enough to make them ineffective. Even one atom of air or light particle can knock the vulnerable qubits off course, causing them to lose their superposition.

That is why the quantum chip in the laboratories of both IBM and Google is located at the bottom of a freezer in a large cabinet with components made of gold and copper, which cool the chip to almost absolute zero of -273.15 ºC. This construction is called a cryostat, and it is the only thing that allows researchers to perform calculations on a quantum chip at all.

This also explains why quantum computers have not contained more qubits up to now. The more qubits they have, the harder it is to keep them in superposition for a while because of the risk of electrical interference from outside increases exponentially with the number of qubits.

Better medicines, smarter artificial intelligence and the solution of big cosmic riddles. These are just some of the scientific advances that the quantum computer may bring in the future.

1. Medical experiments are a thing of the past

Quantum computers make it possible to create, simulate and design molecular structures down to the atomic level. This allows them, for example, to simulate how a new drug will work in a human being — without first testing on humans or animals.

2. New materials see the light of day

New materials that can improve the mobile phone and the PC, and make solar cells and building materials more efficient, will emerge in the wake of the quantum computer. In particular, researchers hope that technology will provide more insight into superconducting materials, which can transport electricity without losing energy.

3. Cosmic riddles are solved

Although researchers took the world’s first picture of a black hole in 2019, we still know very little about the mysterious cosmic phenomena. The quantum computer, which can measure and analyse the smallest components of the universe, may shed new light on black holes.

4. Artificial intelligence is getting smarter

Artificial intelligence is based on so-called neural networks. These are imitations of the extensive network of nerve cells in the human brain that, just like a human being, have to be trained at first. This is a demanding process that can sometimes take weeks. With artificially intelligent quantum algorithms, the process can probably be reduced to seconds. The algorithms will therefore be able to evolve much faster and become ‘smarter’.

Despite the great advances made by Google and IBM in particular, there is still a long way to go before the extremely powerful quantum computer can be found in your home.

If you were to install a quantum computer at home, the sensitive processor would probably have to be able to operate at room temperature. Moreover, Googles quantum computer has ‘only’ beaten a supercomputer with a particularly complicated calculation designed for this purpose. The next milestone is to get a quantum computer to solve a useful problem.

To succeed in this, the quantum computer must be able to work with thousands and perhaps even millions of qubits simultaneously. And that is difficult since the structure of qubits in Google’s and IBM’s quantum computers is like a house of cards that threatens to collapse at the slightest external noise.

But perhaps a third IT giant, Microsoft, has the solution to the problem. Via a so-called topological circuit of quantum bits, this company is trying to circumvent the fragile structure of the quantum computer. The design works like Lego blocks, connecting qubits like bricks in a house and thus making the computer less vulnerable.

Whether the quantum computer will get its final breakthrough at Microsoft, Google, IBM or a fourth party is impossible to predict. One thing is certain, however: the race to get the quantum computer out of the freezing labs and prove the value of the technology has begun in earnest.

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