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Leaked paper claims Google has demonstrated quantum supremacy

by Max Smolaks
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But not everyone is impressed

by Max Smolaks 23 September 2019

Update: The full paper was published in Nature on 23 October 2019

A researcher leading Google’s quantum computing effort claims to have produced a proof of quantum supremacy - a task where a quantum computer considerably outperforms a classic computer.

A paper describing the experiment was accidentally
published on a NASA website, before being promptly removed.

The document, seen by both the Financial Times and New Scientist, details a computational problem that would take 10,000 years to solve using today’s most powerful supercomputer, Summit - built by IBM for Oak Ridge National Laboratory – but which can be solved by an existing quantum tech in less than four minutes.

The news is not entirely unexpected: Google previously said it plans to prove quantum supremacy using Bristlecone, its latest and most powerful quantum chip.

Demonstrating quantum supremacy is an important
step towards making quantum computing useful in the data center. List of potential
applications for quantum calculations includes protein folding in medical research,
machine learning, image recognition, financial modelling, cryptography and even
weather forecasting.

However, not everyone agrees that the reported
experiment falls under the definition of quantum supremacy.

Huge, if true

The paper that’s been turning heads has been written by John Martinis, professor at the University of California, Santa Barbara, who has been in charge of Google’s quantum hardware efforts since 2014.

It details a type of a random
sampling problem that is almost impossible to solve with conventional processors. But true
quantum chips – the kind that need to be operated at temperatures close to absolute
zero (-273.15°C/-459.67°F) – can
reportedly get it done within a few minutes.

The clever bit of maths essentially checks
whether an incredibly long number was truly random.

“To our knowledge, this experiment marks the first computation that can only be performed on a quantum processor,” the paper said.

Quantum computers interact with information
using quantum bits or ‘qubits’. A traditional bit measures either ‘1’ or ’0’. Because
quantum states can be superposed, qubits can measure both ‘1’ and ’0’
simultaneously – just as the famous cat in Schrodinger’s Paradox can be both
alive and dead because it is isolated from the outside world in a coherent
quantum state.

In the experiment, the calculations were performed using Google’s 54-qubit quantum circuit codenamed Sycamore. It’s not even the highest-performing quantum chip at Google, that honor belongs to the 72-qubit Bristlecone, but the more powerful version is reportedly suffering from design issues.

Interestingly, the paper notes that one of the
qubits gave up during the experiment, so technically the alleged quantum
supremacy was proven on a 53-qubit system.

Several of Google’s competitors have disputed the paper’s claims. “It’s just plain wrong,” Dario Gil, head of research at IBM, told the FT, adding that the experiment had no practical applications.

The hardware used by Google was specialized
for the task, he said – and was very far removed from universal quantum
computers that are necessary for doing real-world research.

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