There’s an excellent article in IEEE Spectrum today taking hard look at quantum computing’s (QC) near-term prospects. The idea isn’t to throw cold water on QC’s prospects but to show how far off it may be and remind readers that QC may have narrow use cases. The account also highlight a recent advance in error correction and the use of logical qubits by a Harvard-led team as in indicator of how quickly things can change.

Writer Edd Gent does a nice survey of several quantum obstacles. For example, he cites an observation by quantum researcher Matthias Troyer of Microsoft that the overhead associated with quantum computing can render its advantageous moot.

Gent writes, “Troyer says these gains can quickly be wiped out by the massive computational overhead incurred by quantum computers. Operating a qubit is far more complicated than switching a transistor and is therefore orders of magnitude slower. This means that for smaller problems, a classical computer will always be faster, and the point at which the quantum computer gains a lead depends on how quickly the complexity of the classical algorithm scales.

“Troyer and his colleagues compared a single Nvidia A100 GPU against a fictional future fault-tolerant quantum computer with 10,000 “logical qubits” and gates times much faster than today’s devices. Troyer says they found that a quantum algorithm with a quadratic speed up would have to run for centuries, or even millennia, before it could outperform a classical one on problems big enough to be useful.”

Ouch!

Gent writes, “Nonetheless, there can still be cause for optimism, says Microsoft’s Troyer. Even if quantum computers can only tackle a limited palette of problems in areas like chemistry and materials science, the impact could still be game-changing. “We talk about the Stone Age and the Bronze Age, and the Iron Age, and the Silicon Age, so materials have a huge impact on mankind,” he says.”

The article (Quantum Computing’s Hard Cold Reality Check) is a fascinating fast read.

Link to IEEE Spectrum article, https://spectrum.ieee.org/quantum-computing-skeptics