Free-space laser addressing of ions (AOM/AOD beams) ct_ionaod

An optical bench sends gate light through viewports and a high-aperture objective; acousto-optics set which ion is lit and the light's amplitude, frequency and phase. A multi-channel AOM gives one rf channel per fixed beam — 32 at 355 nm in the 2016 five-qubit Maryland machine, the technology's origin D[585]; an AOD maps rf frequency to angle, so a steered beam reaches any ion D[100]. Hyperfine qubits take a Raman pair — 355 nm for ¹⁷¹Yb⁺ D[586], 532 nm for ¹³³Ba⁺ D[109]; ⁴⁰Ca⁺ optical qubits take one 729 nm beam D[253].
Attributes: optical control at room temperature; coherent errors; bulk optics; one assembly per chain.

Crosstalk. A Gaussian field falls as exp(−d²/w²) — ~10⁻¹² at EURIQA's 0.85 µm waist and 4.43 µm pitch S — yet the neighbour sees up to 2.5% of the target's Rabi frequency D[254]: aberration and scatter set the floor. Published neighbour figures, in differing measures, fall from <4% in 2016 D[585] to <9×10⁻⁴ D[587]. For a Rabi ratio ε, a spectator rotated by εθ loses ≈(εθ/2)², 2.5×10⁻⁴ at ε = 10⁻² for a π pulse S; being coherent, the error compensates — intensity-scaling light-shift pulses cut the AQT demonstrator's 0.5% neighbour figure to 1.3×10⁻⁴ D[253].
Pointing and phase. Jitter δx shifts the Rabi rate by ~(δx/w)² S; Forte sizes its 1.5 µm waist against pointing noise D[100]. At 355 nm, 56 nm of path between counter-propagating arms is 1 rad of gate phase S; Forte configures two of its four paths for phase-insensitive single-qubit gates D[100].
The AOD. θ = λf/v; resolution is aperture time × bandwidth; thermal drift needs in-situ angle calibration G[588]. Duke's UV AOD deflects 6 mrad over a 100 MHz band D[587], i.e. v ≈ 5.9 km/s S. The rf also shifts the optical frequency with position; AQT's crossed AODs cancel it D[253]. ~50 beam diameters of steering D[587] span 25–50 ions at 3–4 µm spacing S. Pairs are served in sequence D[109]: 15 disjoint pairs at Forte's median 672 µs MS gate take ~10 ms S. Field of view and serialisation hold a chain near 30–40 ions S.

Above 40 ions, beyond Helios's 98 ions in a QCCD trap, only claims exist: Tempo's page lists 100 "target" qubits and 99.9% "target fidelity", with no addressing method C[101]. Tsinghua's 512-ion crystal runs global 411 nm beams — free space without addressing D[121].

An assembly, not a wafer: a pulsed UV laser (EURIQA: Coherent Paladin 355-4000) D[254], acousto-optics — fused silica in the UV, TeO₂ in the visible G[588] — objectives and rf synthesis; Duke's module uses a Brimrose AOD D[587]. Gooch & Housego and AA Opto Electronic are also named P[322]; G&H deflectors steer 3,000- and 6,100-atom tweezer arrays too C[504], a supply shared with cx_aod. AQT fits 12 qubits in two 19-inch racks, 2 m², <2 kW C[382].

A multi-channel AOM needs one rf channel per ion at fixed pitch — EURIQA idles two end ions to keep the spacing uniform D[254]; Forte's four AODs, each behind an AOM that sets amplitude, frequency and phase, are designed to reach any of 40 ions — the benchmark ran 36, limited by its photon-detection channels — and free the trapping potential D[100]. Switching (~240 ns) D[587] is negligible; serialisation is the latency — Ba-testbed code cycles take 35–86 ms, all ions shelved to D₅/₂ during mid-circuit readout D[109]. At 10³ ions: ~25 benches plus photonic links S.

Slot 5 of "Trapped ions — linear Paul trap with individual laser addressing" and "Trapped ions — QCCD (transport between zones)". It requires fab_optics (bulk optics above the trap), provides the free-space fields g_ms requires, and is replaced by ct_ionlaser (integrated delivery) and ct_ionmw (laser-free, microwave-driven electronic gates, two-qubit error 8.4(7)×10⁻⁵ D[102]). Sixteen register machines carry it (16 as primary), among them IonQ Aria, Forte, Tempo and the 40-ion Ba testbed; Quantinuum Helios, H1 and H2; AQT IBEX Q1 and LYNX; PIAST-Q; QSCOUT (Quantum Scientific Computing Open User Testbed); the FIAN / Rosatom 70-qubit ion machine; Tsinghua; Innsbruck; Maryland/Duke. Seven cells are ✅; Aria's is 🔎, its beam optics shown only for the 2019 predecessor D[586]; Tsinghua's is 🔎 and shows global beams; Tempo, PIAST-Q and the Rosatom machine are 🔎. Qudoor AbaQ is not among them: its control is undisclosed. AQT and Innsbruck are profiled as ⁴⁰Ca⁺ optical qubits, as their cited papers use D[253]D[255]. Gap G-ionaod is closed, with ion_chain in place of the proposed ion_elec.

Crosstalk is quoted as Rabi ratio, intensity ratio (ε²) or spectator error — Duke calls a Rabi ratio "intensity crosstalk" D[587] — and measured by moving one ion through the beam D[253], by flag ions D[254] or by simultaneous benchmarks D[109]. Forte's 435-pair DRB finds no significant dependence on ion distance but significant out-of-model errors D[100]. Of the vendor pages opened, only AQT's specifies crosstalk, neighbour <1.8×10⁻², as of 2026-09-26 C[382].

Not published: Tempo's species, gate time and addressing method, Aria's own architecture and Qudoor AbaQ's control; and any quantitative figure for rf power per tone, multi-tone intermodulation or AOD thermal pointing drift in ion systems.

Money.

• 2023-12-05 · AQT · 20-qubit two-rack computer for LRZ and Munich Quantum Valley, Bavarian funding · ~EUR 9.8 M · contracted C[323]
• 2025-09-17 · IonQ · acquisition of Oxford Ionics (chip-manufactured traps) · not stated in the release · closed C[18]

Market & supply chain. Lasers, acousto-optics, objectives and rf are merchant parts; ytterbium's UV lines demand expensive, power-limited lasers P[322]. Both architectures serve G2, G3, G6 and G7.

IP & standards. IonQ filings on compensating Raman beam-geometry errors (JP 2024, EP 2025) P[375]; no crosstalk-reporting standard found as of 2026-09-26.

Roadmaps & track record. IonQ (2025-06-13): Tempo, 100 qubits, 2025; 10,000 on one chip, 2027; >2,000,000 by 2030, naming Oxford Ionics 2D traps and photonic links as the means R[132]. Tempo's figures remain targets C[101]; the 2026-04-14 two-system photonic link gave no rate or fidelity C[589]. AQT's LYNX claims QV 32,768 and lower laser phase-noise sensitivity, no qubit count C[128].

Strategic reading. The fastest route to a working 30–40-ion machine and the yardstick for integrated and electronic delivery, but not a scaling path; value moves to trap chips and links.

Confirm if, by 2027-12-31, IonQ publishes Tempo's per-pair gate times, fidelities and addressing method, or an addressed chain above 60 ions is benchmarked; demote if IonQ's next systems ship on electronic or integrated delivery. Open questions. (1) What sets the neighbour floor below 10⁻³ — aberration, scatter or rf intermodulation? (2) Can multi-tone AODs run parallel gates without stray beams? (3) How does pointing drift scale with rf duty cycle? (4) Does double-sided steering hold at 100 ions? (5) When does a photonic link beat a longer chain?