Quantum computer concept art

Google paper claims ‘quantum supremacy’ has been achieved

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A paper published on a Nasa website, before being quickly removed, has described Google’s apparently successful project to build a quantum computer that reaches quantum supremacy.

Quantum computers make use of quantum-mechanical phenomena such as superposition to carry out calculations rapidly. Quantum computers use ‘qubits’ instead of bits: while bits can be either a 0 or a 1, a qubit can represent 0, 1, or any superposition of these two states. While quantum computers are in early stages of development, a quantum computer could theoretically perform calculations exponentially faster than a classical computer.

Quantum supremacy is a milestone in quantum computing, referring to the ability of quantum computer to perform calculations which would not be possible using classical computers.

The Google paper describing this achievement, which was briefly made available on a Nasa website before being removed (Google and Nasa collaborate on developing quantum hardware), was reported on by the Financial Times. Although the original paper is no longer accessible, a plaintext version has been posted online.

According to the paper, Google engineers created a quantum computer with 54 qubits – of which 53 were functional – nicknamed ‘Sycamore’. This is a successor to Google’s previous 72-qubit ‘Bristlecone’, which did not achieve the milestone. The computer was used to perform calculations - performing random operations and printing the results - in 200 seconds which would have taken the most advanced supercomputers an estimated 10,000 years. However, it is worth noting that the calculations were performed on a supercooled quantum rig designed specifically for this purpose and which does not also function as a general-purpose computer.

The paper described the calculations as “an experimental realisation of quantum supremacy on a computational task” which “heralds the advent of a much-anticipated computing paradigm”. The calculations do not serve any practical purpose but rather serve as a demonstration of rapid advances in the field.

Dario Gil, director of research for IBM, told Science News that: “Quantum computers are not ‘supreme’ against classical computers because of a laboratory experiment designed to essentially (and almost certainly exclusively) implement one very specific quantum sampling procedure with no practical applications.”

IBM is among the organisations competing to develop quantum computers capable of delivering practical benefits not possible using classical computers.

Quantum computers – which Google claims could double the pace of Moore’s Law – have raised fears that cryptographic techniques used to transfer data could be rendered insecure on account of their sheer computational might. However, a considerable number of technical hurdles stand between the basic quantum computers tinkered with today and a general-purpose quantum computer capable of operating at room temperature.

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