Quantum supremacy hits theoretical quagmire

Nature mag reports:

Race for quantum supremacy hits theoretical quagmire

It’s far from obvious how to tell whether a quantum computer can outperform a classical one

Quantum supremacy might sound ominously like the denouement of the Terminator movie franchise, or a misguided political movement. In fact, it denotes the stage at which the capabilities of a quantum computer exceed those of any available classical computer. The term, coined in 2012 by quantum theorist John Preskill at the California Institute of Technology, Pasadena1, has gained cachet because this point seems imminent. According to various quantum-computing proponents, it could happen before the end of the year.

But does the concept of quantum supremacy make sense? A moment’s thought reveals many problems. By what measure should a quantum computer be judged to outperform a classical one? For solving which problem? And how would anyone know the quantum computer has succeeded, if they can’t check with a classical one? ...

Google, too, is developing devices with 49–50 qubits on which its researchers hope to demonstrate quantum supremacy by the end of this year2. ...

Theorist Jay Gambetta at IBM agrees that for such reasons, quantum supremacy might not mean very much. “I don’t believe that quantum supremacy represents a magical milestone that we will reach and declare victory,” he says. “I see these ‘supremacy’ experiments more as a set of benchmarking experiments to help develop quantum devices.”

In any event, demonstrating quantum supremacy, says Pednault, “should not be misconstrued as the definitive moment when quantum computing will do something useful for economic and societal impact. There is still a lot of science and hard work to do.”

I can't tell if this article was written by Richard Haughton or Philip Ball.

Just reading between the lines here, I say that this means that IBM and Google will soon be claiming quantum supremacy, but they are preparing journalists with the fact that their new quantum computers won't really outdo any classical computers on anything.