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.