Google researchers claimed quantum supremacy last week, shortly followed by rebuke from its rivals.
On the company’s quantum computer, scientists led by John Martinis achieved a computation in 200 seconds that would have taken 10,000 years on a classical computer.
Writing in the journal Nature, the team said they performed a fixed set of operations that entangles 53 quantum bits, or qubits, into a quantum superposition state to solve a random number sampling task.
Brooks Foxen from Google’s Martinis Group, said: "It is likely that the classical simulation time, currently estimated at 10,000 years, will be reduced by improved classical hardware and algorithms, but, since we are currently 1.5 trillion times faster, we feel comfortable laying claim to this achievement."
Joe Incandela, UC Santa Barbara particle physicist, said: “The team has demonstrated the ability to reliably create and repeatedly sample complicated quantum states involving 53 entangled elements to carry out an exercise that would take millennia to do with a classical supercomputer.”
Professor Incandela said that the accomplishment, which represents two decades of quantum computing research, marks “a threshold of a new era of knowledge acquisition”.
But the rivals and members of the quantum community have been slightly more conservative in their praise. Intel commended Google on its “demonstration” but said the next step will be “to build a system that will enable us to address intractable challenges — in other words, to demonstrate ‘quantum practicality’”.
And this seems to be where the key difference lies. Perhaps by publishing their pioneering quantum capabilities, Google researchers have inadvertently established the difference between quantum supremacy and quantum practicality.
Professor Winfried Hensinger, director of the centre for quantum technologies at Sussex University, said: “The problem they [Google] picked is a completely utterly useless problem. The next step will be to solve useful problems.”
By definition, Google’s random number generator task is achievable on a classical computer – albeit after 10,000 years of computation. On this basis, it has had cold water poured on it by rival IBM, which has a quantum computing effort of its own.
"Because the original meaning of the term ‘quantum supremacy, as proposed by John Preskill in 2012, was to describe the point where quantum computers can do things that classical computers can't, this threshold has not been met," IBM researchers wrote in a blog post.