What You Shouldn't Know About Quantum Computers

Reception of the article

• Several readers find it a clear, accessible explanation of what quantum computers are and are not.
• Others criticize it for mixing abstraction layers (e.g., using transistors as an analogy) and for glossing over deep technical issues like scalable error correction.

Feasibility and Power of Quantum Computing

• One camp argues quantum computing may never be “usefully” realizable or significantly more powerful than classical computing in practice, especially at large scale.
• Another camp points to fault-tolerance threshold theorems and current experimental progress as strong evidence that large, useful machines are physically possible, though challenging.
• There is debate over whether skepticism implies new physics would be required, or merely that engineering might be impractically hard.

Cooling, Noise, and Scaling

• Long subthread on thermodynamics: whether cooling costs and thermal noise scale polynomially or worse with the number of qubits and volume.
• Some argue cooling difficulty grows sharply at very low temperatures and large scales; others emphasize geometry and error correction can mitigate this, and more qubits do not necessarily require lower temperatures.
• Several commenters distinguish between temperature limits and error-correction overhead.

State of Quantum Error Correction

• Question raised: has anyone demonstrated a single fully “usable” logical qubit?
• Linked experimental work shows substantial error reduction but only with heavy pre/post-selection; still far from target logical error rates (~10⁻⁸).
• Multiple comments repeat that the main milestone is crossing the error-rate threshold where overhead becomes finite and scalable.

Quantum Supremacy and Factoring Timelines

• Progress on factoring with Shor’s algorithm is seen as minimal; past demonstrations are criticized as “compiled” or non-robust.
• A co-author of a cited forecasting paper clarifies their predictions are conditional on smooth continuation of current trends and says more meaningful metrics than “largest integer factored” show steady progress.
• Some readers view predictions like “90% chance of factoring RSA‑2048 by ~2060” as overconfident or “delusional”; others stress that long-term probabilistic forecasts reflect present information, not certainty.

Cryptography and Complexity Perspective

• Discussion notes that quantum computers are expected to efficiently solve certain problems (e.g., discrete logarithms, factoring) but are not believed to solve arbitrary NP problems.
• Emphasis that quantum speedups come from interference patterns, not brute-force parallelism over 2ⁿ states.

Usefulness, Hype, and Industry Dynamics

• Multiple comments assert there are effectively no present-day, broadly useful quantum computing applications; current devices are mostly research or niche (e.g., annealers).
• Some call the investor-facing story around quantum computing a “con” in its expectations, while acknowledging the underlying science is real.
• Comparisons are drawn to hype in AI and blockchain, though AI is noted as already commercially useful.

Meta: arXiv Use and Popularization

• Brief debate over whether uploading a long popular-science-style PDF to arXiv is appropriate; others point out there is a dedicated “physics and society” category for such material.
• Short side discussion on children’s physics books and whether they emphasize superficial analogies versus core conceptual substance.