Quantum supremacy:How does it actually work and what is the Sycamore computer

Scientists have finally claimed to reach quantum supremacy, a landmark in an industry that could change the world.
But the announcement has been wrapped in confusion and controversy. Though quantum computing could bring profound new processing power to the world, it is also incredibly complicated both to understand and to test.

The milestone is revealed in a new paper that has been long-rumoured but is now finally published in the prestigious journal Nature. And the world is finally scrutinising what exactly google means by quantum supremacy, whether its claim stand up – and what happens now.

Here is what you need to know

How does quantum computing work?
To understand how a quantum computer works, it’s important first to understand how a traditional one works. Everything from the phone in your pocket to the computer in your desk – and all the other places that computers appear – do so using the paradigm of classic computing, which has stayed strong for years but which quantum computers could compete with, if not displace.
In a traditional computer, everything in the memory is represented as a series of bits, which work as a binary system: they are either 1 or 0, on or off. Those bits can be assembled into the vast and complex information processing systems that we use every day, by stringing them together and analysing the data they together represent.

A quantum computer works instead with qubits, not bits – they are no longer binary, but instead can be in a number of different states. By exploiting the unusual behaviour described in quantum mechanics, scientists are able to build quantum computers, which operate at that more complex and therefore more powerful level.
What is Google’s ‘Sycamore’?
The Sycamore chip is a 54-qubit processor. That is relatively limited, and is one of the many reasons that the discovery is not practically useful – researchers want a 100-qubit or even 200-qubit system before they are really able to put it to the test, and see whether the dreams of quantum computing are realised.
But the big breakthrough is just how high-fidelity and fast the gates that make up the computer are. Scientists have lauded the precision with which the system works, and it is that which allowed Google to make its announcement.