Compute · Updated July 2026Momentum · accelerating ↗
How close are we to a quantum computer that doesn't break?Can we build a quantum computer that actually works?
or, simply: Can we build a quantum computer that actually works?or, precisely: How close are we to a quantum computer that doesn't break?
Error-corrected qubits have crossed below threshold; the open question is scaling from one logical qubit to the millions a useful machine needs.Today's quantum computers are too error-prone to trust. Fixing that means going from a handful of good qubits to millions.
We are here
Universal toolkit remains tiny — Eight trapped-ion physical qubits hosted three error-detected logical qubits for a measurement-free Grover search over eight items. Next up — IBM targets Starling availability (expected 2029).
01 · Where we stand
Four tests between here and the goal
Each threshold is a falsifiable claim with a named next test. We move the meter only when a result is public.
Below-Threshold Error ScalingBigger codes work better✓ Achieved · Dec 2024
100%
Proven byA 101-physical-qubit distance-7 memory reached 0.143% error per cycle.
Corrected Memory Beats HardwareProtection pays for itself✓ Achieved · Dec 2024
100%
Proven byThe distance-7 logical memory exceeded the best physical-qubit lifetime by 2.4±0.3 times.
Integrated Universal Logical OperationsCompute while correctingEarly
35%
Next testRun a multi-logical-qubit universal circuit through repeated correction with a lower total failure rate than its physical implementation.
Utility-Scale Fault-Tolerant ComputationDo useful work economicallyEarly
8%
Next testIBM's 2029 Starling claim is a visible test: 200 logical qubits and 100 million gates must be independently characterized.
THRESHOLDS — Thresholds for Fault-Tolerant Quantum.
Scale
Measured Goal region
NOTE — This follows the candidate file's recommended metric and keeps only Google's comparable superconducting surface-code memory sequence. A memory error per correction cycle is not a logical-gate error, and changes in chips, decoders and cycle circuits prevent treating this as a pure hardware trend. The 10^-12 goal is an application estimate per logical operation, not a demonstrated threshold. Neutral-atom, ion, colour-code and post-selected results are kept out of this line because their metrics are not interchangeable.
02 · How we got here
The record behind the verdict
Major events set large; context events set small but never hidden. Everything below the TODAY rule is a schedule, not a result.
Computing Becomes Quantum moved the field from feynman proposes quantum simulation to deutsch defines universal machine. The results narrowed the next question without closing it.
1982
Feynman proposes quantum simulationTheory
Feynman argued that simulating quantum physics efficiently may require a computer governed by quantum mechanics.
Codes Make Reliability Possible moved the field from shor makes reliability consequential to kitaev introduces topological protection. The results narrowed the next question without closing it.
1994
Shor makes reliability consequentialTheory
Shor gave polynomial-time quantum algorithms for factoring and discrete logarithms, motivating very long reliable computations.
Correction Enters Hardware moved the field from surface-code threshold quantified to trapped ions correct errors. The results narrowed the next question without closing it.
2002
Surface-code threshold quantified
Dennis and colleagues analyzed 2D surface codes and showed protection can improve without limit below a critical error rate.
The Breakeven Experiments moved the field from cat code reaches breakeven to fault-tolerant control beats physical. The results narrowed the next question without closing it.
2016
Cat code reaches breakevenExperiment
A corrected bosonic qubit lasted 320 microseconds, 1.1 times its best physical constituent, without post-selection.
Below Threshold, Not Useful moved the field from larger surface code barely wins to ibm targets starling availability. The results narrowed the next question without closing it.
2023
Larger surface code barely winsExperiment
Google's distance-5 memory reached 2.914% error per cycle versus 3.028% at distance 3, only a 4% relative reduction.
Events outside the declared eras moved the field from repeated detection reduces failures to darpa utility deadline arrives. The results narrowed the next question without closing it.
2015
Repeated detection reduces failures
A nine-qubit superconducting device cut retrieval failures 8.5-fold after eight error-detection cycles, using post-selection.
The learning curves and comparisons that justify each threshold's percentage. Every series is measured, with the source event linked in the timeline above.
The log descent
A billion-fold cliff, drawn honestly
1.4 billion×still to go
NOTE — This follows the candidate file's recommended metric and keeps only Google's comparable superconducting surface-code memory sequence. A memory error per correction cycle is not a logical-gate error, and changes in chips, decoders and cycle circuits prevent treating this as a pure hardware trend. The 10^-12 goal is an application estimate per logical operation, not a demonstrated threshold. Neutral-atom, ion, colour-code and post-selected results are kept out of this line because their metrics are not interchangeable.
The distance-3, distance-5 and distance-7 memories used 17, 49 and 101 physical qubits respectively; the duplicate 2023 points are different code distances, not elapsed-time growth.NOTE — The distance-3, distance-5 and distance-7 memories used 17, 49 and 101 physical qubits respectively; the duplicate 2023 points are different code distances, not elapsed-time growth.Suppression strengthened from a marginal 1.039-fold distance-3-to-5 improvement to a 2.14-fold reduction for each two-distance increase on Willow.NOTE — Suppression strengthened from a marginal 1.039-fold distance-3-to-5 improvement to a 2.14-fold reduction for each two-distance increase on Willow.Two breakeven landmarks, but not a clean platform series: 2016 used a bosonic cat code, whereas 2024 used a 101-qubit surface code.NOTE — Two breakeven landmarks, but not a clean platform series: 2016 used a bosonic cat code, whereas 2024 used a 101-qubit surface code.Vendor roadmap targets for Starling and Blue Jay, not measured systems or independently validated logical qubits.NOTE — Vendor roadmap targets for Starling and Blue Jay, not measured systems or independently validated logical qubits.IBM's stated circuit-capacity objectives; the roadmap explicitly says its goals may change or be withdrawn.NOTE — IBM's stated circuit-capacity objectives; the roadmap explicitly says its goals may change or be withdrawn.
Distance 33 % error/cycle
Distance 52.9 % error/cycle
COMPARISON — Google's first larger surface code improved logical error by only about 4%, showing how narrow the first below-scaling signal was.
Distance-7 logical memory291 microseconds
Best constituent physical qubit119 microseconds
COMPARISON — Willow's corrected logical memory lasted 2.4 times longer than its best constituent physical qubit.
Demonstrated distance 7101 physical qubits
Projected distance 271457 physical qubits
COMPARISON — Even Google's extrapolated 10^-6 memory would require about fourteen times the physical qubits used by its demonstrated distance-7 memory.
Willow memory error0.00 probability/cycle
Factoring-scale target0.00 probability/operation
COMPARISON — Numerically, Google's memory-cycle error is roughly 1.4 billion times the 10^-12 operation target, though the two metrics differ.
04 · What it unlocks
If the remaining tests pass
Downstream capabilities, drawn dashed because they depend on results not yet in.