Rydberg tweezer array — alkali (Rb/Cs) on the map bar: Alkali Rydberg gates

The architecture in the report (§8.3)

8.3.7 Alkali Rydberg gates — Rydberg tweezer array — alkali (Rb/Cs) (atom_rb)

The idea. A rubidium or caesium atom in an optical tweezer holds a hyperfine clock qubit, coherent for 12.6 s in a 6,100-atom caesium array [D][138], [139]. A global laser pulse drives neighbours toward a Rydberg state, where one excitation blocks the other: a CZ gate in ~270 ns [D][4]. Acousto-optic deflectors (AODs) move atoms or whole code blocks so any pair can meet: connectivity is a program. The price is the clock: transport and imaging, not the gate, set a derived QEC round of 1.31 ms [S] (§7.4), 1–4.5 ms measured [D][4], [31]. The bet: qubits that cost laser power, not fabrication, and transversal logic between moved blocks, with constant syndrome rounds per logical gate, buying back the transport time [S][152].

What it needs. The gate requires the alkali atom and global Rydberg pulses from free-space lasers (ct_laser). The high-rate and algorithmic-fault-tolerance codes require AOD transport: moving one block onto another pairs every qubit with its partner under one pulse. Algorithmic fault tolerance requires correlated, loss-aware decoding, which requires transversal circuits; its gain, 1.73(13)× over a loss-blind decoder, rests on four rounds of one run [D][4], none in real time. Continuous reload replaces one-shot loading and conflicts with the stored qubits, which see scattered cooling light; a reservoir carried 0.5 m by conveyors mitigates it [D][144]. Carrier, encoding, gate, interconnect and fabrication hold one technology each, code five, decoder four: the hardware is fixed, the code open. No atom–photon cavity link has joined two modules; AOD bandwidth runs out near 10⁴ atoms [S] (§2.4).

Where it stands. Sixteen machines, seven devices, five gate-capable. The largest, the 448-atom fault-tolerant processor (Harvard/MIT/QuEra), holds the best two-qubit error, 5.0×10⁻³ (CZ fidelity 99.3–99.6% by randomised benchmarking) [D] (Table 8.3), and ran surface codes d=3→5 with 2.14× suppression over four rounds and up to 96 logical qubits [D][4]. Gemini-class (QuEra; 99.2% global CZ, one shot per second [C][137]) ran logical magic-state distillation [D][147]; Sqale (Infleqtion) entangled 30 logical qubits in error-detecting blocks [C][151]; Orion Alpha/Beta/Gamma (Pasqal) publishes no gate error. The largest arrays have no gate: the 6,100-qubit tweezer array [D][138], [139] and the continuously reloaded 3,000-atom machine, run over 2 h [D][144]. Libra (QuEra, 2028: >256 logical qubits at 10⁻⁶) [R][162], [163] and Pasqal's Vela, Centaurus (500+ qubits, 2028) and Lyra (2029) are plans [R][166], [167], [875]; Google's 2026 track names no species [P][158]. Rows with no documented cell — 6: Hanyuan-1, Hanyuan-2, Qinghe-1, the Moscow State University prototype, the Quantum X Labs platform.

Exceptions and borrowings. The boundary with the analogue simulator architecture (atom_analog) runs through layers 2 and 3: carrier, transport, control, readout and fabrication are shared, but the analogue qubit is the ground–Rydberg pair and its computation continuous Hamiltonian evolution, with no code, decoder or link above. Pasqal crosses it both ways: Orion, filed here, lists the analogue encoding and evolution as alternates; Fresnel, filed there, lists the hyperfine qubit and blockade CZ. One apparatus runs either mode, so the line divides modes, and a machine is filed by its primary one: hybrids, not errors. Orion's chip-optics alternate cites nothing. Gemini-class and Libra list fast readout as an alternate neither machine shows: mislabelled. Libra's ten-layer fit rests on a cavity cell specifying no link. The reload machine is dated August 2026 from a review; its paper is from 2025 [D][144]. The Moscow prototype has no entangling gate yet a two-qubit error from a press statement; Quantum X Labs names no species; Hanyuan-2's inter-core link is undisclosed: data gaps. The alkaline-earth architecture shares gate, transport, reload, decoder and cavity; carrier and erasure encoding divide them.

The next test. Confirm by end-2027 (§5.2): a memory of ≥100 rounds with reloading at Λ>2 (error suppression per code-distance step) on an alkali array, and a gate-capable alkali processor above 1,180 qubits, the family frontier the alkaline-earth architecture has held since 2023 (§8.5, F1b). Demote if Libra slips past 2028, or two-qubit fidelity stalls at 99.9%, the ceiling a 2026 review sets for the standard CZ, with no new gate scheme [S][140].

What the builders say. Harvard's Mikhail Lukin says the 448-atom processor combined, for the first time, all essential elements of scalable error-corrected computation in one architecture [D][845]; Caltech says its 6,100-atom array has quantity and quality together [D][138], [139]. QuEra promises Libra on Amazon Braket in 2028, with over 256 logical qubits at a logical error of 10⁻⁶ [R][162], [163]. Infleqtion, after entangling 30 logical qubits in error-detecting blocks in September 2026, says it is on track for 100 in 2028 and 1,000 by 2030 [R][168]. Pasqal's 2025 roadmap runs from 2 logical qubits in 2025 to 20 in 2027, 100 in 2029 and 200 in 2030 [R][166], [167]; in January 2026 it moved Vela, over 256 qubits, from 2027 to 2026 [R][390].

Machines of this architecture (register: 16, of them 7 devices, 5 gate-capable). Pasqal — Pasqal Centaurus (planned, 500), Vela (announced, 256), Orion Alpha / Beta ("Ruby") / Gamma (deployed, 140), Pasqal Lyra (planned); Infleqtion — Sqale (deployed, 100), Infleqtion Illinois neutral-atom quantum computer (IQMP, Chicago) (announced); QuEra — Libra (planned, 10,000), Gemini-class (deployed, 260); Zhongke Kuyuan (Wuhan, CAS) — Hanyuan-2 (announced, 200), Hanyuan-1 (deployed, 100); Caltech (Endres group) — 6,100-qubit tweezer array (demonstrated, 6,100); Harvard / MIT — continuously reloaded 3,000-atom machine (demonstrated, 3,000); Harvard / MIT / QuEra — 448-atom fault-tolerant processor (demonstrated, 448); Lomonosov Moscow State University with the Russian Quantum Center — 72-qubit neutral-atom (Rb) quantum computer prototype (50 qubits in Dec 2024) (announced, 72); Quantum X Labs Inc. (Nasdaq: QXL) — Quantum X Labs neutral-atom platform (50+ qubits, claimed) (announced, 50); Zhongqi Wuliang (Shanghai, CAS SIOM spin-off) — Qinghe-1 (Qinghe No. 1, 清河一号) (announced).

Cells outside the architecture's slots (8). Hanyuan-2: L9 undisclosed where the architecture expects a technology; Pasqal Centaurus: L7 undisclosed where the architecture expects a technology; Pasqal Centaurus: L8 undisclosed where the architecture expects a technology; Pasqal Lyra: L7 undisclosed where the architecture expects a technology; Pasqal Lyra: L8 undisclosed where the architecture expects a technology; Orion Alpha / Beta ("Ruby") / Gamma: L2 Ground–Rydberg analogue qubit (enc_gr, alternate borrowed from another architecture); Orion Alpha / Beta ("Ruby") / Gamma: L3 Analogue Rydberg Hamiltonian evolution (g_rydanalog, alternate borrowed from another architecture); Libra: L9 undisclosed where the architecture expects a technology.