Trapped ions — linear Paul trap with individual laser addressing on the map bar: Laser-addressed chain

The architecture in the report (§8.3)

8.3.5 Laser-addressed chain — Trapped ions — linear Paul trap with individual laser addressing (ion_chain)

The idea. One static chain in a linear Paul trap: its collective motional modes (cx_bus) couple every pair, so a Mølmer–Sørensen gate entangles any two ions without moving them, and each ion gets its own acousto-optically steered beam (ct_ionaod). The qubit is hyperfine (Yb⁺, Ba⁺) or the optical S–D qubit of ⁴⁰Ca⁺ (enc_opt: AQT, Innsbruck, PIAST-Q). It gives up length: N ions share N modes in a fixed bandwidth, so gates slow as the chain grows, to a median 672 µs on Forte's 30 ions [D][100], [101]. The bet: connectivity is free inside a chain of tens of ions; scale is bought at its edge with photonic links between chains, the modular architecture of Monroe et al. [S][252].

What it needs. The gate requires spin–motion coupling and free-space laser fields, which require bulk optics. The two defining technologies conflict (open): mode crowding makes the gate slower and less faithful with each ion; the mitigations (zoned short chains, electronic gates on ≤4-ion segments) belong to other ion architectures. qLDPC and high-rate codes require the chain's all-to-all: four logical qubits in 18 ions [D][109]. Encoding offers three mutually replacing technologies (hyperfine, optical, metastable); carrier, gate, connectivity, readout and interconnect have one technology each; the interconnect, Ion–photon photonic link, carries the scaling bet at a best 250 s⁻¹ [D][116] against ~10⁴ s⁻¹ needed [S] (§2.3). Layer 10 is drawn too narrowly: planar surface-electrode chips only, while IBEX Q1 runs in a machined blade trap [D][253] and the 512-ion crystal in a monolithic 3D trap [D][121].

Where it stands. Sixteen machines, thirteen devices: IonQ's Aria, Forte and 40-ion Ba-133 qLDPC testbed; AQT's IBEX Q1 and LYNX (15 qubits, quantum volume 32,768 in May 2026 [C][128]); PIAST-Q; Sandia's QSCOUT; Qudoor's AbaQ; the Innsbruck and Maryland/Duke traps; Tsinghua's analogue 512-ion simulator [D][121]. Tempo counts as a 64-qubit demonstration (IonQ's #AQ 64 run on a development system) without a published gate error; the 100-qubit product with its "99.9% fidelity" is listed for late 2026 [C][100], [101]. Quantum Art's Perspective (a 1,000-qubit multi-core system) [C][125] and the FIAN / Rosatom 70-qubit machine (35 ions as qudits) are announcements. The largest gate-capable device is Tempo's 64-qubit development register, which has no published gate error; the largest with published gate errors, the 40-ion testbed, reached memory break-even within error bars, 3.95(68) s logical against 3.84(48) s physical, with leakage post-selection [D][109]. Maryland/Duke's 3.0×10⁻³ is a logical Clifford error after correction, not a physical figure, and is no longer counted [D][254]; Table 8.3's best error is therefore the vendor's 4.0×10⁻³ on Aria and Forte [C][99]. IonQ, the largest vendor, has put its successor, Superion 256, on electronic gates [C][119].

Exceptions and borrowings. Maryland/Duke carries three: that logical figure; a Bacon–Shor subsystem code with no technology (∅G-subsystem; its high-rate alternate encodes one qubit); a link cell merging a separate experiment, the 250 s⁻¹ record [D][116], with Oxford's 9.7 s⁻¹ link [D][115]: a lineage, not a machine. Innsbruck borrows ion shuttling (segmented traps) and the magic-state technology [D][255]: a lineage spanning both laser architectures, and a code layer drawn too narrowly; its measurement-free feedback is a gap (∅G-coherent). IBEX Q1's shuttling alternate describes AQT's research traps, not the product: mislabelled. Forte's CMOS-foundry alternate projects IonQ's SkyWater route, first used for the 256-qubit chips of 2026 [C][119], onto a 2022 machine. The testbed and Tempo decode by offline beam search (∅G-beam), outside layer 8; Tempo's code cell repeats the testbed's run. Tsinghua's crystal is analogue under global beams (∅G-isinganalog, ∅G-crystal): the architecture is drawn too widely, and ions lack an analogue architecture. Quantum Art's link is filed as undisclosed, yet its paper segments one crystal into cells with reconfigurable optical potentials [S][256]: neither bus nor transport, a gap. Qudoor's control and all Rosatom cells: data gaps. Borrowers: the electronic-control architecture takes the motional bus (JION, QUARTET, Superion 256); planqc's MAQCS the optical qubit.

The next test. The link decides: confirm if an ion–photon link exceeds 10³ s⁻¹ by end-2027; demote if none passes ~10× the 250 s⁻¹ record by end-2028. At chain scale, confirm if per-pair errors and gate times appear for Tempo or any chain above 40 ions by end-2027; if disclosure stays at headline level while IonQ ships electronic gates, the architecture narrows to racks and laboratories, leaving early fault tolerance to other ion architectures.

What the builders say. IonQ reached #AQ 64 (its algorithmic-qubit benchmark) on a Tempo development system in a single ion chain with all-to-all connectivity [C][839]; in April 2026 it linked two commercial machines by photons, calling scaling beyond one chip essential [C][589]. AQT claims quantum volume 32,768 for LYNX, its rack-mounted series, first units due in Q4 2026 [C][128], [129]. Quantum Art cuts long chains into cores with laser-defined boundaries and promises 1,000 physical and up to 100 logical qubits in 2027, a million physical by 2033 [R][840]. FIAN reached 50 qubits with qudits, ions using more than two levels, doubling the count cheaply [C][841]; in August 2026 it and the Russian Quantum Center moved to planar traps, where ions shuttle between small arrays instead of one chain [C][842].

Machines of this architecture (register: 16, of them 13 devices, 11 gate-capable). IonQ — Tempo (demonstrated, 64), 40-ion Ba-133 qLDPC testbed (IonQ: a Tempo engineering test system) (demonstrated, 40), Aria (deployed, 32), Forte / Forte Enterprise (deployed, 30); Alpine Quantum Technologies — AQT LYNX (demonstrated, 15), IBEX Q1 (Marmot / PINE) (deployed, 12); Quantum Art — Montage (first-generation QaaS system, up to 50 qubits) (announced, 50), Perspective (1,000-qubit multi-core system) (announced); IQOQI Innsbruck (Austrian Academy of Sciences) with the University of Innsbruck (M. Joshi, C. Roos) — Innsbruck trapped-ion analog quantum simulator (up to 51 ions) (demonstrated, 51); Lebedev Physical Institute (FIAN) and the Russian Quantum Center, Rosatom roadmap — 70-qubit ion quantum computer (FIAN / Rosatom roadmap) (announced, 70); Poznan Supercomputing and Networking Center (PCSS) — PIAST-Q (deployed, 20); Qudoor (Guokaike) — Aba|Qu 1.0 (Tiansuan-1, 天算1号) (deployed); Sandia National Laboratories — QSCOUT (Quantum Scientific Computing Open User Testbed) (deployed, 6); Tsinghua University (Duan group) — 2-D site-resolved ion simulator (demonstrated, 512); University of Innsbruck — University of Innsbruck trapped-ion demonstrator (Institut für Experimentalphysik) (demonstrated, 20); University of Maryland / Duke University — Maryland / Duke Quantum Center (EURIQA lineage) (demonstrated, 13).

Cells outside the architecture's slots (13). 40-ion Ba-133 qLDPC testbed (IonQ: a Tempo engineering test system): L8 ∅G-beam (Atlas gap — beam-search decoder (Delfosse) for the qLDPC codes, run offline; no Atlas node for search ); Montage (first-generation QaaS system, up to 50 qubits): L5 undisclosed where the architecture expects a technology; Montage (first-generation QaaS system, up to 50 qubits): L9 undisclosed where the architecture expects a technology; Perspective (1,000-qubit multi-core system): L5 undisclosed where the architecture expects a technology; Perspective (1,000-qubit multi-core system): L9 undisclosed where the architecture expects a technology; Aba|Qu 1.0 (Tiansuan-1, 天算1号): L5 undisclosed where the architecture expects a technology; 2-D site-resolved ion simulator: L3 ∅G-isinganalog (Atlas gap — global laser-driven spin–spin coupling; analog Ising simulator in a 2-D ion crystal, not a); 2-D site-resolved ion simulator: L4 ∅G-crystal (Atlas gap — static 2-D Coulomb crystal, power-law all-to-all coupling (511 neighbours), no transport); University of Innsbruck trapped-ion demonstrator (Institut für Experimentalphysik): L4 Ion shuttling (QCCD, junctions, grid traps) (cx_qccd, alternate borrowed from another architecture); University of Innsbruck trapped-ion demonstrator (Institut für Experimentalphysik): L8 ∅G-coherent (Atlas gap — measurement-free: syndromes mapped into an auxiliary register, coherent feedback unitary r); Innsbruck trapped-ion analog quantum simulator (up to 51 ions): L3 ∅G-isinganalog (Atlas gap — analog long-range Ising / XY interaction from a bichromatic beam coupling all transverse m); Innsbruck trapped-ion analog quantum simulator (up to 51 ions): L4 ∅G-crystal (Atlas gap — static linear Coulomb chain, long-range (J0 = 185 rad/s, alpha = 0.97 at 51 ions), no tran); Maryland / Duke Quantum Center (EURIQA lineage): L7 ∅G-subsystem (Atlas gap — Bacon–Shor [[9,1,3]] subsystem code on 13 ions: FT prep, FT measurement, logical rotation,).