When will a quantum computer be capable of operating with over 1,000 fully error-corrected logical qubits?

TL;DR

My median forecast is June 13, 2033; the 10th–90th percentile range is June 9, 2029 to June 27, 2044, with 5% probability after December 31, 2050. The aggressive targets are QuEra’s 1,000-plus logical qubits in 2028–2029 and IonQ’s 1,600 in 2028, while IBM’s structured plan crosses the threshold at 2,000 in 2033+. Width and depth have not yet been combined at scale: Google has one below-threshold surface-code memory, Atom Computing has a small toric-code memory tested through 90 syndrome cycles, and Quantinuum’s 48–94-logical-qubit headline uses post-selection or error detection, so the central forecast remains the early-to-mid 2030s.

Context

The resolution bar is narrower than “useful quantum computer.” One system must publicly instantiate at least 1,001 logical qubits at once and run active error correction, including repeated syndrome extraction and decoding. It need not run a valuable algorithm or reach a specified logical error rate. But encoding, error detection, discarded shots, simulation, and counts spread across machines do not qualify.

As of the August 26, 2026 at 00:23 UTC evidence cutoff, the public record still separates scale from correction. Large encoded computations exist, and long repeated-QEC experiments exist, but they are not the same experiments. That is why raw “logical qubit” headlines overstate the starting point for this question. The 70-qubit IBM result used syndrome post-selection, while the 2025 neutral-atom paper used up to 448 atoms but characterized repeated QEC on a distance-five logical memory for only a handful of rounds.

Evidence

There is no large historical sample of comparable logical-qubit roadmaps. The closest reference class is a mix of physical-hardware roadmaps and the first generation of explicit fault-tolerant roadmaps. The evidence window here runs from IBM’s September 15, 2020 roadmap through the cutoff. Four major programs—IBM, QuEra, Quantinuum, and IonQ—provide direct dated logical-qubit projections, which is too small and heterogeneous for a reliable empirical slippage distribution.

These analogues cut both ways. IBM and Quantinuum have delivered named physical systems near schedule. QuEra’s logical product sequence changed before its first roadmap matured. I therefore discount late-2020s logical-qubit promises, but not to zero.

The cleanest evidence for active correction is narrow. Google’s Willow paper reported a 101-physical-qubit distance-seven surface-code memory with a 0.143% logical error per cycle and below-threshold scaling; a distance-five version ran with an integrated real-time decoder. Atom Computing’s June 2, 2026 preprint extended a small neutral-atom toric-code memory to as many as 90 syndrome-extraction cycles with mid-circuit measurement and atom replacement. These are strong depth results, not wide multi-logical-qubit systems.

The widest results fail the strict test. Quantinuum’s February 25, 2026 paper used 98 physical qubits to benchmark 48–94 logical qubits, but the paper explicitly describes post-selection, and the 94-qubit code is error-detecting. A separate March 4, 2026 fault-tolerant-algorithms paper ran a 12-logical-qubit QAOA circuit on 97 physical qubits, but the 12-qubit runs used zero QEC cycles and retained 69.8%–82.2% of shots; active-QEC algorithm tests in that paper were narrower. IBM’s July 28, 2026 70-qubit result likewise achieved its error suppression after syndrome post-selection. Under this question’s rules, none establishes a frontier near 50–100 fully corrected logical qubits.

The strongest early route is high-rate QEC on neutral atoms or trapped ions. QuEra projects more than 1,000 logical qubits from more than 20,000 physical qubits in 2028–2029. IonQ projects a jump from 100–256 physical and 12 logical qubits in 2026, to 10,000 physical and 800 logical in 2027, then 20,000 physical and 1,600 logical in 2028. The required one-year physical-system jump is roughly 40–100 times, before allowing for uniform fidelity, parallel control, measurement, decoding, and correction. I treat those dates as a real early tail, not the modal case.

External institutions point to the same broad center. The Department of Energy’s June 23, 2026 Quantum Genesis announcement targets fault-tolerant systems with logical-qubit counts in the low hundreds in 2028. DARPA said on March 10, 2026 that a utility-scale quantum computer by 2033 now seemed likely; its program had evaluated 20 companies, advanced 11 to Stage B, and moved two earlier performers to Stage C. Utility scale is not the same milestone, but hundreds in 2028 and utility around 2033 support an early-2030s center for a 1,001-qubit demonstration.

A useful edge comes from the mismatch between spatial and temporal scale. Google’s March 24, 2026 neutral-atom announcement says neutral-atom arrays had reached about 10,000 qubits but still needed deep circuits with many cycles, while superconducting systems had deep-cycle experience but needed architectures with tens of thousands of qubits. This shows why physical-qubit count alone is not the main forecast variable. The milestone requires the space and time dimensions to work together.

I model the delay from August 26, 2026 at 00:23 UTC as T = 0.5 + LogNormal(log(6.3), 0.79) tropical years. The 0.5-year offset is a practical engineering floor. The 6.3-year residual median puts the total median delay at 6.8 years. The log-scale spread of 0.79 represents multiplicative schedule risk across fabrication, fidelity, control, decoding, QEC integration, and public validation.

The center is later than the 2028–2029 roadmaps because the present strict frontier is small and the systems must scale several hard layers at once. The tail is not larger because multiple architectures compete, raw neutral-atom scale is already high, and the resolution does not demand commercial usefulness or a long algorithm.

What's non-obvious

The headline count is the wrong state variable. A 12-logical-qubit experiment can have zero active QEC cycles, while a small-code experiment can run correction for 90 cycles. The target arrives when one architecture combines width, repeated syndrome extraction, decoder throughput, replacement or reset, and adequate fidelity in the same run. Most coverage reports whichever of width or depth looks bigger.

The resolution is also easier than the roadmaps it cites. QuEra targets a logical error rate of 10⁻⁹ and IBM targets a billion-gate machine, but this question sets no minimum code distance, error rate, circuit depth, or economic value. A shallow but genuine 1,001-logical-qubit active-QEC demonstration would qualify. I read this as offsetting part of the roadmap-slippage penalty and keeping meaningful probability in 2029–2031.

Uncertainties

The first gap is definitional. Repeat-until-success state preparation, software-tracked corrections, erasure handling, terminal decoding, and a small number of syndrome rounds can sit near the boundary between active correction and post-selection. Independent consensus may lag the first announcement, and a disputed claim could end in annulment.

The second gap is scaling data. No public experiment shows how high-rate codes behave when thousands of logical blocks, parallel gates, mid-circuit measurements, real-time decoding, and loss replacement run together. The most valuable new evidence would be a no-post-selection demonstration of at least 100 simultaneous logical qubits over many QEC cycles, with scaling across code distance and public shot-level data.

The third gap is the reference class. There are too few matured logical-qubit roadmaps to estimate slippage statistically. Physical-qubit roadmaps are more numerous, but they understate the difficulty of full-stack QEC. The 5% post-2050 tail covers correlated failure of low-overhead codes, severe integration bottlenecks, long disclosure disputes, and architectures that scale in count without scaling in corrected operation.