The single milestone that decides when quantum computing becomes practical has a dry name and enormous stakes: fault tolerance. Here is what it means and why the race to reach it is heating up.
Today's quantum computers are real, impressive, and error prone. Their qubits are fragile, and small mistakes creep into every calculation. For now, that limits them to short tasks and careful demonstrations. The whole field is organized around fixing this, and the finish line has a name. Fault tolerance is the point at which a quantum computer can correct its own errors faster than they appear, so it can run long, useful programs reliably.
It is tempting to track progress by counting qubits, the way we once counted megahertz. That misses the point. A machine with thousands of noisy qubits can still be useless if errors pile up before it finishes. Quality matters more than raw quantity. The goal is not just more qubits, but qubits stable enough, and connected well enough, to trust. This is why a smaller, cleaner machine can outperform a larger, noisier one.
The fix is clever. Instead of trusting any single fragile qubit, you spread one unit of information across many physical qubits and use the group to constantly check and repair itself. The result is called a logical qubit, and it is far more stable than any of its parts. The cost is steep, since each logical qubit can take many physical ones, but the principle works. It turns an unreliable component into a dependable one, which is exactly the trade computing has made before in other forms.
For years, error correction was mostly theory. That has shifted. Google's Willow processor, unveiled at the end of 2024, showed something the field had been waiting for: as the team made the logical qubit larger, the error rate went down rather than up. Crossing that threshold, where bigger means better instead of noisier, is the proof of principle that error correction scales. IBM, meanwhile, has published a detailed roadmap aimed at a fault-tolerant machine around the end of the decade. When serious companies put dates on paper, it usually means the remaining problems look like engineering, not mystery.
The contest is broad and well funded, which is healthy. Different groups are betting on different kinds of qubits, from superconducting circuits to trapped ions to neutral atoms and photons, and each approach has real strengths. No one knows yet which will win, or whether several will coexist for different jobs. What matters for everyone watching is that the competition is pushing quality, stability, and error correction forward on every front at once.
Fault tolerance is not here yet, and that is fine. The right posture is neither hype nor dismissal. Watch the error rates and the roadmaps, not the qubit counts. Learn which of your problems are the kind quantum will help with, so you recognize the moment when it arrives. And build relationships with the platforms doing the work now, because access and know-how compound. The companies that treat the run-up to fault tolerance as preparation, rather than spectator sport, will be ready the day the machines are.
Jason Kumpf tracks the milestones that will make quantum computing practical. He is Head of US Revenue at Razorpay, a board advisor, angel investor, and speaker. More about Jason.