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Quantum computers are all over the news, but what are they and how do they differ from conventional computing? If they can be built economically and at scale quantum computers will harness properties that extend beyond the limits of classical physics to offer us exponential gains in computing power. Classical computers are made of bits, a unit of information that can either be a 0 or a 1. But in a quantum computer, the basic unit, known as a qubit, can represent both 0 and 1 at the same time, a state known as superposition.
By stringing together qubits the number of states that they could represent rises exponentially, enabling it to compute millions of possibilities instantaneously. The applications of this type of machine could revolutionise fields from cryptography to chemistry, ranging from materials science, agriculture, and pharmaceuticals, not to mention artificial intelligence and energy.
So far, the challenge has been to scale up the number of qubits to perform useful calculations while reducing the number of errors that the qubits are prone to. This week Google has published a landmark paper in the scientific journal Nature. It claims to have built a processor that can perform a very specific calculation in 200 seconds that would take today's most powerful computer 10,000 years to complete. This demonstration is known as quantum supremacy.
This is just the first step towards creating a useful quantum computer. Next, scientists will have to build a scaled-up version that can perform real world, useful calculations, thus achieving the promise of quantum computing.
