Quantum computers perform calculations based on the probability of an object's state before it is measured - instead of just 1s or 0s - which means they have the potential to process exponentially more data compared to classical computers.

Classical computers carry out logical operations using the definite position of a physical state. These are usually binary, meaning its operations are based on one of two positions. A single state - such as on or off, up or down, 1 or 0 - is called a bit.

In quantum computing, operations instead use the quantum state of an object to produce what's known as a qubit. These states are the undefined properties of an object before they have been detected, such as the spin of an electron or the polarization of a photon.

Rather than having a clear position, unmeasured quantum states occur in a mixed 'superposition', not unlike a coin spinning through the air before it lands in your hand. These superpositions can be entangled with those of other objects, meaning their final outcomes will be mathematically related even if we don't know yet what they are.

The complex mathematics behind these unsettled states of entangled 'spinning coins' can be plugged into special algorithms to make short work of problems that would take a classical computer a long time to work out. Such algorithms would be useful in solving particular mathematical problems, like finding very large prime numbers.

Since prime numbers are so important in cryptography, it’s likely that quantum computers would quickly be able to crack many of the systems that keep our online information secure. Because of these risks, researchers are already trying to develop technology that is resistant to quantum hacking and on the flip side of that, it’s possible that quantum-based cryptographic systems would be much more secure than their conventional analogues.

Researchers are also excited about the prospect of using quantum computers to model complicated chemical reactions, a task that conventional supercomputers aren’t very good at all. In July 2016, Google engineers used a quantum device to simulate a hydrogen molecule for the first time. Shortly after that IBM has managed to model the behaviour of even more complex molecules. Eventually, researchers hope they will be able to use quantum simulations to design entirely new molecules for use in medicine

Building a functional quantum computer requires holding an object in a superposition state long enough to carry out various processes on them. Unfortunately, once a superposition meets with materials that are part of a measuring system, it loses its in-between state in what's known as decoherence and becomes a boring old classical bit.

Devices need to be able to shield quantum states from decoherence, while still making them easy to read. Different processes are tackling this challenge from different angles, whether it's to use more robust quantum processes or to find better ways to check for errors.

For the time being, classical technology can manage any task thrown at a quantum computer. Quantum supremacy describes the ability of a quantum computer to outperform their classical counterparts.

Google, IBM and a handful of startups are racing to create Quantum computers and achieve Quantum Supremacy. But the quantum future isn't going to come easily and there's no knowing what it'll look like when it does arrive. At the moment, companies and researchers are using a handful of different approaches to try and build the most powerful computers the world has ever seen.

In November 2017, when IBM announced it had built a 50-qubit quantum computer. However, it was far from stable, as the system could only hold its quantum microstate for 90 microseconds, a record, but far from the times needed to make quantum computing practically viable. Just because IBM has built a 50-qubit system doesn’t necessarily mean they have cracked supremacy and it definitely doesn’t mean that they have created a quantum computer that is anywhere near ready for practical use.

Quantum computing is by no means a two-horse race. Californian startup Rigetti is focusing on the stability of its own systems rather than just the number of qubits and it could be the first to build a quantum computer that people can actually use. D-Wave, a company based in Vancouver, Canada, has already created what it is calling a 2,000-qubit system although many researchers don’t consider the D-wave systems to be true quantum computers. Intel, too, has skin in the game. In February 2018 the company announced that it had found a way of fabricating quantum chips from silicon, which would make it much easier to produce chips using existing manufacturing methods

Everybody isn't convinced that quantum computers are worth the effort. Some mathematicians believe there are obstacles that are practically impossible to overcome, putting quantum computing forever out of reach. Time will tell who is right.

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