Google promised quantum supremacy um... well... last year. Made for some great headlines, with the press breathlessly announcing that the quantum era has arrived. Only, it didn't. Internally, there are two quantum computing groups who are competing for resources and don't seem to collaborate.

Rigetti plans a 120 qubit system, but has yet to calibrate it, so I'm not holding my breath. And their qubits still have astonishingly low connectivity and the fidelity of their gates is so low that a larger qubit count won't get them anywhere. In other news, they laid off half of their software team because their chip isn't actually useful, so a full-fledged software stack was somewhat premature (if quite elegant). Ex-employees have some great opinions about the culture; check glassdoor.

Microsoft's QC efforts are fascinating, but AFAIK they don't even have a plan to build a computer. Word on the street is that huge egos and a lack of production experience are conspiring to prevent progress.

And the funny thing about these quantum computing efforts: nobody even has a plan for error correction. For all Scott Aaronson rails against DWave... he doesn't dig deep into gate-model efforts, to expose their flaws. And strangely, he's still focused on coherence time of DWave's qubits.

There's a fundamental difference between gate-model and adiabatic qubits: gate-model qubits in the "0" state are at a ground level, and "1" is an excited state -- whereas DWave's qubits have "+1" corresponding to clockwise current, "-1" corresponding to counterclockwise current; and both are ground states of the qubit. Coherence time is roughly the amount of time it takes an excited state to decay into a ground state. Adiabatic transitions begin, remain, and end in ground states, barring external perturbations -- and if such an event occurs, a low coherence time is actually preferable. Higher coherence times are still beneficial to adiabatic quantum computers like DWave's and Google's G-mons, since it boosts long-range interactions between qubits, but it isn't the showstopper that Aaronson hypes it to be.

So gate-model quantum computing is promising, in theory. But there are some very real, very difficult roadblocks to clear before we get there. And for all that DWave gets omitted from such discussion... well, the theorists say that adiabatic and gate-model quantum computing are actually equivalent[1]. Wake me up when somebody else can factor arbitrary 10-bit integers[2] -- and even so... 10-bit factoring problems don't really scream "quantum computing may be here soon" -- more like "1970 called, and says quantum computing is crushing it."

[1] https://physicsworld.com/a/quantum-adiabatic-and-quantum-cir... [2] https://www.dwavesys.com/sites/default/files/14-1002A_B_tr_B...