Hold your horses, quantum "supremacy" isn't all that

Bursting the quantum computer bubble. From, who else? @skdh https://t.co/2dK1NAIGLc

— John Horgan (@Horganism) August 2, 2019

Sabine Hossenfelder, Quantum supremacy is coming. I won't change the world, The Guardian, Aug. 2, 2019:

Today’s largest quantum computers have about 20 superconducting qubits. The next generation of chips, those expected to achieve quantum supremacy, will hold at least 50.

Quantum supremacy will be a remarkable achievement for science. But it won’t change the world any time soon. The fact is that algorithms that can run on today’s quantum computers aren’t much use. One of the main algorithms, for example, makes the quantum computer churn out random numbers. That’s great for demonstrating quantum supremacy, but for anything else? Forget it.

The mammoth task of making the machines useful has been eclipsed by quantum enthusiasm. The Boston Consulting Group drew on more than 100 experts and 150 peer-reviewed publications for its recent report on quantum computing. It sees the first applications coming in three to five years, with quantum computers taking on materials simulations that slash costly, time-consuming lab tests. Further ahead their use will spread, and in future decades productivity gains brought about by quantum computers will top $450bn (£372bn) annually, the report asserts.

Well, let’s not get carried away. To compute something useful – say, the chemical properties of a novel substance – would take a few million qubits. But it’s not easy to scale up from 50 qubits to several million. In fact, the challenge is formidable.

The trouble is that quantum systems are exceptionally fragile. To maintain their quantum behaviour, qubit chips are enclosed in sealed boxes fitted with vacuum pumps to remove stray air molecules, or cooled to a fraction of a degree above absolute zero. More qubits means more fridges, more connections and more expense. Worse, these devices are exquisitely sensitive to the smallest disturbances – even footsteps can send them awry. Even when housed in far-flung shelters and accessed through the cloud, it is not clear that a million qubit machine would ever remain stable for long enough to function.