A quantum computer that runs algorithms of practical value, with logical error rates low enough that the answer can be trusted. It does this by encoding each logical qubit in many noisy physical qubits and correcting errors faster than they accumulate.
Scope
In scope: the full machine that error-corrects a computation, built here from physical qubits, a real-time decoder, cryogenic control and refrigeration, and links between modules. Out of scope: noisy intermediate-scale machines without error correction, quantum sensors and quantum networks for their own sake. The decoder is covered by quantum/real-time-qec-decoder and the module links by quantum/quantum-interconnect.
Readiness
TRL 4 (4 of 9)
A distance-7 surface-code memory below threshold has been shown in the laboratory; no logical algorithm of practical value has run, and the wiring, refrigeration and decoding for a million-qubit machine are not built.
What reaching the target would change, and for whom. No claim is stronger than the evidence it cites.
Riskreported
A quantum computer with less than a million noisy qubits could factor a 2048-bit RSA integer in less than a week, under the estimate's assumptions of a uniform gate error of 0.1%, a surface-code cycle of 1 microsecond and a control reaction time of 10 microseconds.
Why this target. Gidney's RSA-2048 estimate runs for less than a week at a 1 microsecond cycle, about 6e11 cycles (6.05e5 s divided by 1e-6 s; durations from gidney2025how). A single logical qubit must then fail with probability well under 1/(6e11), about 1.7e-12, per cycle; with many logical qubits the requirement is lower still, so 1e-12 is a floor of the order of magnitude, not a precise budget.
Average gate infidelity of a two-qubit gate, 1 - F_avg, as measured by randomized or interleaved randomized benchmarking. A process (Pauli) infidelity, as cycle or cross-entropy benchmarking report, is converted with r_avg = d r_process / (d + 1) = 0.8 r_process for d = 4, and the card says so. Lower is better.
Current (2025-01-01)6 × 10⁻⁴
Target0.001
Limit–
Conditions. Best reported single pair: 60 ns gate on two fluxonium qubits, randomized benchmarking.
Why this target. Gidney's RSA-2048 estimate assumes a uniform gate error of 0.1% across a square grid of qubits. The best pair already beats it, so the gap is uniformity across a million qubits, not the best pair.
Note. as_of is the start of the publication year (PRX Quantum volume 6, 2025); the exact date was not in the abstract. One pair, not a uniform array.
Number of physical qubits operated together in one device. Higher is better.
Current (2024-12-09)101 qubit
Target10⁶ qubit
Limit–
Conditions. Qubits used by the distance-7 surface-code memory on the Willow processor.
Why this target. Upper bound of the RSA-2048 resource estimate: less than a million noisy qubits (gidney2025how), down from 20 million in the 2019 estimate.
Single pairs of superconducting qubits reach two-qubit gate fidelity of 99.94% (error 6e-4) with stability over 24 days, but a million-qubit machine needs every pair near that level at once, with leakage and crosstalk held down. The Willow memory ran at 0.143% logical error per cycle at distance 7, short of the target by about nine orders of magnitude. Closing it means both lower physical error and larger code distance on many more qubits.
Approaches
Fluxonium qubits with direct two-qubit gates (TRL 3)lin2025days
The largest error-corrected memory in the evidence uses 101 qubits; the target is up to a million. A coaxial line per qubit from room temperature does not scale, so control and readout must move into the cryostat. Cryo-CMOS multiplexing has worked below 15 mK without degrading relaxation times, and superconducting digital demultiplexing has run a multi-qubit system, both at laboratory scale.
Correlated errors from cosmic rays and radioactivity
highscientific unknownlayer: devicepromising
Muons and gamma rays create quasiparticle bursts that cause correlated errors across a chip, which error correction cannot absorb. A measurement on a 63-qubit processor separated the contributions of muons and gamma rays. Back-side phonon downconversion cut correlated poisoning by two orders of magnitude on three-qubit chips; it has not been shown on a million-qubit array.
Approaches
Phonon downconversion with back-side normal-metal reservoirs (TRL 4)iaia2022phonon
The Willow decoder averaged 63 microseconds at distance 5, six times the 10 microsecond reaction time assumed in the RSA-2048 estimate, and at a cycle time of 1.1 microseconds, far from 1 microsecond at thousands of logical qubits. FPGA decoders report tens to hundreds of nanoseconds per measurement round in modeled-noise studies, which is not the same quantity as end-to-end latency in a running experiment.
Each wired qubit adds passive heat load from cables and active load from signal dissipation. The strongest dilution refrigerator in the evidence delivers 2 mW at about 100 mK with a base temperature of 6.6 mK; no source in the atlas states the load of a million-qubit machine. Resource models of modular machines predict power and thermal load, and point to splitting the machine across cryostats.
A multinode machine needs entanglement between cryostats. Internode gates may be two to three orders of magnitude noisier and slower than local operations, and a systems analysis finds link performance must improve by 10 to 100 times.
Real-time quantum error-correction decoderEvery error-correction cycle needs its syndromes decoded before the next logical operation that depends on them. Need: Reaction time of 10 microseconds, the figure assumed in the RSA-2048 resource estimate (gidney2025how).
Dilution refrigerationSuperconducting qubits operate at about 10 mK, and every control line and amplifier adds heat to that stage. Need: Enough cooling power, in one cryostat or several linked, for the heat load of up to a million physical qubits and their wiring.
Cryogenic control electronicsOne coaxial line per qubit does not scale to a million qubits; control and readout electronics must sit in the cold.
Quantum interconnectA machine of up to a million qubits is unlikely to fit in one cryostat, so modules must be linked by quantum channels.
Required by
Nothing in the atlas depends on it yet.
Arrows point from a technology to what it requires. Select a node to open it.