Zuchongzhi 2.1

Raveh Neeman

doi:10.5281/zenodo.22674814

USTC / Hefei National Laboratory · superconducting circuits · RETIRED (demonstrated Oct 2021) · 66 physical qubits · access: lab-only

architecture: Transmon lattice with tunable couplers · Open on the map

Register profile — the machine's variant of its architecture

qubit type: tunable transmon

gate mechanism: tunable coupler

connectivity: square lattice

control: room-temperature RF

control placement: room-temp

readout: dispersive

gate evidence: a published figure (source class not yet tagged)

codes: surface-17

flags: claim later eroded, second hand numbers, source not confirmed

Technologies by layer — the machine's cell per layer

1 Qubit carrier	Transmon · primary ▣ Fig. 1a (66-qubit, 110-coupler flip-chip processor schematic); Fig. 1b (qubit circuit) ✅ 66 tunable transmons in an 11×6 array (Oct 2021); numbers second-hand from a survey
2 Encoding	Bare physical qubit (no encoding) · primary ◌ 🔎 Bare two-level subspace — Computational subspace of an anharmonic oscillator; leakage to \|2⟩ is the price.
3 Gate mechanism	Tunable-coupler CZ / iSWAP · primary ▣ Fig. 1b (qubit, coupler and readout circuit schematic); Fig. 2c (Pauli error of 99 2Q gates) ✅ tunable coupler (110 couplers); 2Q ≈97–98% (era-typical, second-hand)
4 Connectivity / transport	Static nearest-neighbour lattice · primary ▣ Fig. 1a (11x6 lattice, 110 couplers); Fig. 3a (topology diagram, 60 used qubits) ✅ square lattice, degree 4; 11×6 array with 110 tunable couplers
5 Control	Room-temperature electronics + per-qubit coax/flex · primary ▣ Fig. 1a (second chip carries all control lines) ✅ room-temperature RF
6 Readout	Dispersive microwave readout (+TWPA, Purcell) · primary ▣ Fig. 1b (readout circuit schematic); Fig. 2a (readout error of 60 qubits) ✅ dispersive
7 Code	Rotated surface code (+ yoked variants) · primary ▤ abstract; results ✅ d=3 CSS surface code (17 of 66 qubits), up to 11 cycles, MWPM decoding (sweep 7 Oct 2026, source read)
8 Decoder	— none — nothing in this layer ▤ 🔎 no decoder (no QEC)
9 Interconnect	— none — nothing in this layer ▣ Fig. 1a (single flip-chip module: qubit chip + control-line chip; no inter-module link) ✅ monolithic single module, no interconnect
10 Manufacturing	Superconducting-qubit lithography (Al/AlOx/Al junctions, Nb wiring, 300 mm) · primary ▣ Fig. 1a (two sapphire chips combined by flip-chip technique) ✅ Superconducting-qubit lithography (Nb/Al JJ, 300 mm) — IBM Albany 300 mm / Anderon foundry; Google Santa Barbara; Rigetti ABAA trimming (97.4% frequency-targeting success); OQC 500-qubit wafer-scale…

evidence: ✅ 8 / 10

Pictures

Every picture carries the story of what it shows and its credit line.

A paper figure, drawn rather than photographed: (a) a 3D render of a flip-chip processor, a translucent sapphire qubit chip floating above a larger wiring chip marked with Chinese characters; (b) a grid of cross-shaped qubits with coupler bars and a two-qubit-plus-coupler circuit. Fig. 1 of Yulin Wu, Wan-Su Bao et al., arXiv 2106.14734 (2021-06-28), showing the Zuchongzhi processor: two sapphire chips, 66 qubits and 110 couplers. Notice that every pair of neighbouring transmons is linked through its own tunable coupler. “Fig. 1 — Device schematic of the Zuchongzhi quantum processor (two sapphire chips; 66 qubits and 110 couplers)” by Yulin Wu, Wan-Su Bao, Sirui Cao, Fusheng Chen, Ming-Cheng Chen, et al., arxiv.org/abs/2106.14734, CC BY 4.0 (creativecommons.org/licenses/by/4.0/)

A data figure of three heat maps, one square cell per qubit or coupler, coloured blue to red by error rate in percent with the value printed inside. Fig. 2 of Yulin Wu, Wan-Su Bao et al., arXiv 2106.14734 (2021-06-28), reporting single-qubit-gate, two-qubit-gate and readout performance for the 56 qubits and 94 couplers of the Zuchongzhi processor used in random circuit sampling. It is a data plot, not hardware; notice how errors vary from site to site when the whole array runs simultaneously. “Fig. 2 — Single-qubit gate, two-qubit gate and readout performance (56 qubits and 94 couplers used in RCS)” by Yulin Wu, Wan-Su Bao, Sirui Cao, Fusheng Chen, Ming-Cheng Chen, et al., arxiv.org/abs/2106.14734, CC BY 4.0 (creativecommons.org/licenses/by/4.0/)