The boffins behind quantum computing have not solved some of the gargantuan technical challenges that would have to be overcome ever to make quantum computing work.

Experts estimate that the number of qubits needed for a useful quantum computer, one that could compete with your laptop in solving certain kinds of interesting problems, is between 1,000 and 100,000.

The number of continuous parameters describing the state of such a useful quantum computer at any given moment must be at least 2**1,000, which is to say about 10**300.

This number is greater than the number of subatomic particles in the observable universe. So basically a useful quantum computer needs to process a set of continuous parameters that is larger than the number of subatomic particles in the observable universe.

It is unimaginable how to keep errors under control for the 10300 continuous parameters that must be processed by a useful quantum computer. Quantum-Computing theorists have succeeded in convincing the public that this is possible.

The article said that even without considering these impossibly large numbers, it's sobering that no one has yet figured out how to combine many physical qubits into a smaller number of logical qubits that can compute something useful.

“It is not like this hasn't long been a key goal.... On the hardware front, advanced research is underway, with a 49-qubit chip (Intel), a 50-qubit chip (IBM), and a 72-qubit chip (Google) having recently been fabricated and studied. The eventual outcome of this activity is not entirely clear, especially because these companies have not revealed the details of their work.”

The article suggests that despite all the fanfares about quantum computing, interest in the technology is running thin. A few decades is the maximum lifetime of any big bubble in technology or science, and after a certain period, too many unfulfilled promises have been made, and anyone who has been following the topic starts to get annoyed by further announcements of impending breakthroughs.

“What's more, by that time all the tenured faculty positions in the field are already occupied. The proponents have grown older and less zealous, while the younger generation seeks something completely new and more likely to succeed."

He advises quantum computing researchers to follow the advice of IBM physicist Rolf Landauer. Decades ago Landauer warned quantum computing's proponents that they needed a disclaimer in all of their publications.

"This scheme, like all other schemes for quantum computation, relies on speculative technology, does not in its current form take into account all possible sources of noise, unreliability and manufacturing error, and probably will not work."