(Economist) The Economist lands in the middle of IBM’s challenge to Google’s claim of quantum supremacy with an editorial stance that “IBM is right technically. Practically, it makes little difference.”
The task that Google’s engineers tested their machine with is called circuit sampling. It involves measuring the outputs of randomly wired circuits made of qubits. The Economist says that “. . .circuit sampling is a toy problem with little practical use”. Google picked it as a demonstration because it is mightily difficult for a classical machine to do at all, whereas a well-behaved quantum computer finds it trivial. Google used a 53-qubit machine.
Not so fast, said IBM—or, rather, not so slow. The chief problem Summit faced is that when simulating 53-qubit circuits it would run out of memory. This means that, were anyone actually trying to run the simulation, they would have to use a less memory-hungry but much slower algorithm to do so. IBM pointed out that Summit also has plenty of hard-disk space.
The classical-computing yardstick against which its performance was putatively measured was Summit, a machine at Oak Ridge National Laboratory that is, at the moment, the fastest in the world. Summit would be able to compute bthe job in a mere 2½ days. Therefore, according to IBM, Google had not shown quantum supremacy after all.
Technically, IBM is right. How much it matters is another question. Two and a half days is, after all, still about 1,200 times longer than 3 minutes.