Electronic microwave gate (ions, laser-free: near-field or static gradient) g_elec

An entangling gate on hyperfine ion qubits driven entirely by currents in the trap chip. Oscillating currents in electrodes tens of micrometres from the ion produce a microwave field whose gradient, not its amplitude, couples spin to the shared motional mode; a state-dependent force closes a loop in phase space and imprints a geometric phase, as a Mølmer–Sørensen gate does, with a ~10 GHz field replacing two laser beams. Demonstrated at NIST Boulder in 2011 (76(3)%, 20 ns single-qubit pulses) D[444], brought to useful fidelity at Oxford in 2016 with dynamically decoupled ⁴³Ca⁺ clock qubits D[445], industrialised by Oxford Ionics — the Ballance/Harty spin-out of that group, part of IonQ since 2025 — as Electronic Qubit Control C[446]. A parallel lineage at Sussex (Hensinger), its spin-out Universal Quantum, and eleQtron's MAGIC drives global microwave fields across a static gradient P[328], [447]; the near-field variant here holds the records.

Attributes (technology graph):

• Carrier affinity: fully natural — the qubit is an atomic ion; only the trap is fabricated.
• Characteristic time: 2×10⁻⁴ s per entangling operation, deterministic, not heralded.
• Readout: not defined by this node; it inherits the host ion's fluorescence detection.
• Mobility: shared motional bus within a zone, ions transported between zones.
• Control modality and placement: microwave, sources at room temperature.
• Error structure as the code sees it: Pauli plus a coherent component.
• Manufacturing: microfabricated surface trap with buried current traces.

Gate rate is set by the microwave gradient at the ion and the Lamb–Dicke parameter; both are geometric. Halving the ion–electrode distance roughly doubles the gradient but raises anomalous heating steeply (surface noise near d⁻⁴), so speed is bought against motional decoherence — hence durations of 120–226 µs, not sub-microsecond. There is no photon-scattering floor, the dominant fundamental error of laser gates, which is why the achievable ceiling is higher D[102].

What replaces it is a.c. Zeeman shift from the field's non-gradient component, magnetic-field noise, and residual spin–motion entanglement at finite temperature. The first two are attacked with clock qubits and dynamical decoupling D[445]; the third bound everything until the 2025 "smooth gate", which ramps the gate detuning to adiabatically eliminate spin–motion entanglement and tolerate a hot mode — it ran at mean phonon number n̄ = 9.4(3), above the Doppler limit, with error ≲5×10⁻⁴ even hotter D[102]. The residual error is largely coherent — miscalibrated phase and gradient amplitude — which a code sees as correlated rather than depolarising noise, so logical extrapolations assuming Pauli noise run optimistic. Moving the floor further needs lower trap-surface noise and better microwave amplitude and phase stability, not new physics.

Best demonstrated: two-qubit error 8.4(7)×10⁻⁵ (2025-10) on a laboratory chip D[102]. Typical at scale: no gate figure above ten qubits is published — the 2024 device giving 99.97(1)% two-qubit and 99.99916(7)% single-qubit fidelity is a seven-zone chip controlling up to ten qubits D[257], and eleQtron's 30-ion JION, deployed 2026-09-03, launched without a gate fidelity. That gap is the most important fact about this node.

Dominant terms today: temperature-dependent residual spin–motion entanglement and coherent control error. The headline is an estimate from subspace-leakage randomised benchmarking, not tomography D[102]. Gate duration is 225.8 µs in 2025 and ≈120 µs (two 60 µs pulses) in 2024 D[102], [257].

The trap is a surface-electrode chip with buried current-carrying traces and local tuning electrodes in a standard semiconductor process; IonQ's framing is that control lives on "classical semiconductor chips" built in "existing semiconductor fabs" C[446]. That claim is now vertically integrated: IonQ closed the SkyWater Technology acquisition (~$1.8 B, announced 2026-01-26, closed 2026-07-31) Cfact[19], giving it a US 200 mm trusted foundry instead of a merchant relationship. Packaging is the named weak point: Oxford Ionics uses Bay Photonics for the electrical, photonic and electrostatically shielded packaging of high-density trap devices C[448]. No yield, uniformity, defect-density or per-qubit cost figure is published by any actor as of 3 Sep 2026. Export exposure runs through the US BIS interim final rule of 2024-09-06, which created ECCN 4A906 for quantum computers (34-qubit floor with error-rate tiers) plus 3A904/3B904 for enabling equipment fact[301]: a ≥34-qubit electronic-gate system meeting the error tiers falls inside it, and the UK-design/US-parent structure makes licensing a design constraint.

A laser-gate machine of comparable ambition needs many wavelengths and per-zone optical addressing — Helios uses at least seven laser wavelengths and 1,228 electrodes D[97]. The electronic gate deletes the gate lasers, leaving light only for cooling, state preparation and readout, and substitutes room-temperature microwave sources plus d.c. electrode drivers. Per-qubit I/O becomes a mixed-signal ASIC problem — coherent microwave channels and many d.c. lines — a familiar scaling exercise rather than an optical one.

The wall moves rather than disappears. At 10³ qubits it is the count of independent microwave channels and their phase coherence, since amplitude and phase errors are the leading coherent term. At 10⁴ it is routing current-carrying traces, with on-chip dissipation and zone-to-zone crosstalk; no actor has published a crosstalk or heating figure for a 2D array. At 10⁶ nothing in the public record connects this gate to a demonstrated 2D trap. Control-loop latency demands are modest — millisecond-class syndrome cycles suffice.

The node sits on the architecture "Trapped ions — electronic qubit control (laser-free, microwave-driven gates)" (IonQ/Oxford Ionics, eleQtron, QUDORA) as its primary gate, and is the alternate gate on "Trapped ions — QCCD (transport between zones)" (Universal Quantum). It requires a trapped atomic ion as carrier and chip-integrated microwave control as signal source; it provides nothing downstream that the laser gate does not, and directly replaces the laser Mølmer–Sørensen gate. The switching price is one-directional: buried traces and electrode geometry are co-designed with the gate, so an electronic-gate machine cannot fall back to lasers, while a laser machine can in principle add microwave electrodes. Here a natural, unfabricated carrier is steered by purely electronic control — a semiconductor supply chain driving an atomic qubit. Contribution to the derived clock: 2.3×10⁻⁴ s per entangling gate. Derived clock = sum of the syndrome round: gate layers + transport + readout + reset for the architecture ≈1.5×10⁻³ s, gate layers 1.4 ms of it; on a multi-zone machine transport dominates instead (Helios ~55 ms per full-width layer D[97]), so the gate's speed advantage is invisible at product scale. The neighbouring empty slot is the cryogenic version: nothing published combines electronic gates with a cryogenic trap, which is where the heating-versus-gradient trade would be won.

The headline 8.4(7)×10⁻⁵ comes from subspace-leakage randomised benchmarking at Doppler temperature, not from tomography or interleaved RB against an independent reference D[102]. Two-qubit RB twirls coherent errors into an effective depolarising rate, understating the coherent residual, and says nothing about crosstalk to spectator ions — the term that will decide performance at scale. No independent group has replicated the electronic gate above 99.9%: the 2016 Oxford D[445] and 2011 NIST D[444] results are the only non-Oxford-Ionics near-field microwave gates on record, and neither eleQtron nor Universal Quantum has published a comparable fidelity as of 3 Sep 2026. The company line "99.99% two-qubit gate fidelity" C[446] rounds the preprint's 1 − 8.4(7)×10⁻⁵ — consistent, but with no error bar and no width.

The 225.8 µs gate duration of the 2025 record is not stated in the abstract of arXiv:2510.17286. Not published: a patent family or patent count for Oxford Ionics / IonQ Electronic Qubit Control; any delivery or milestone under Universal Quantum's €67 M DLR contract (four-year term from 2022-11) as of 2026-09-03; eleQtron's ion species, qubit count, fidelity and gate time, MAGIC being described only qualitatively; the value of the Innovate UK / DSIT Quantum Missions Pilot award to Oxford Ionics; and any crosstalk, heating-rate or on-chip dissipation figure for an electronic-gate trap chip.

Money.

• 2022-11-02 · Universal Quantum · contract · €67 M · German Aerospace Center (DLR); two machines in four years, multi-chip system up to 100 qubits · — · announced P[328]
• 2025-03-11 · Oxford Ionics · programme award (Quantum Missions Pilot, "Q-Surge") · undisclosed · DSIT and Innovate UK · — · announced C[448]
• 2025-04-03 · Oxford Ionics · DARPA QBI Stage A selection · — · DARPA · — · selected fact[243]
• 2025-09-17 · IonQ · M&A, Oxford Ionics (announced 2025-06-09) · $1.075 B · — · — · closed Cfact[18]
• 2025-10-12 · IonQ · equity · $2.0 B at $93/share, after $1.0 B on 2025-07-08 · — · cash $3.0 B · closed Cfact[326]
• 2025-11-06 · IonQ · DARPA QBI Stage B selection, up to $15 M each · — · DARPA · — · selected fact[65]
• 2026-04-27 · Quantum Art · Series A extension · $140 M, from $100 M on 2025-12-10 · — · — · closed Pfact[125]
• 2026-05-05 · eleQtron · Series A · €57 M · Schwarz Digits lead, with EIC Fund, Earlybird, Ankaa Ventures, Precitec, NRW.BANK · backlog >€54 M · closed Pfact[129], [447]
• 2026-07-31 · IonQ · M&A, SkyWater (announced 2026-01-26) · ~$1.8 B · — · — · closed Cfact[19]
• 2026-Q2 · IonQ · revenue · $80.1 M, +287% YoY; FY guidance $280–290 M · — · cash $3.0 B · reported Cfact[326]

Market & supply chain. There is no merchant market for electronic ion gates. The enabling assets are trap-chip fabrication (in-house at IonQ via SkyWater), microwave sources and amplifiers (commodity RF, low concentration risk) and specialist packaging — Bay Photonics is a genuine single point of failure for the UK line. Concentration risk is corporate rather than industrial: one company holds the record, the patents and the fab. Unit economics are unquotable; nobody publishes cost or power per qubit. The goals that pay for it are G3 (early fault tolerance) and G7 (deployable systems): the case for deleting gate lasers is manufacturability and field-deployability, not speed. G6 is untouched — the node provides no photonic interface.

IP & standards. Oxford Ionics describes Electronic Qubit Control as patented C[446], and the $1.075 B acquisition price is best read as a purchase of that portfolio plus the team; no patent family number, database-sourced count or litigation could be verified as of 3 Sep 2026 (Google Patents assignee search is robots-blocked). No standards body or consortium is specific to this gate.

Roadmaps & track record. (promised on · promised for · status as of 2026-09-03): IonQ, 2025-06-13 · 256 qubits at 99.99% in 2026 · slipped to commissioning in H1 2027 Rfact[132]. IonQ, 2025-06-13 · 10,000 physical qubits on one chip in 2027 and 2 M physical / 40–80 k logical by 2030 · no 2D-trap heating, gate-time or interconnect data published Rfact[132]. Universal Quantum, 2022-11-02 · two machines including up to 100 qubits within four years · no delivery announced as the term elapses P[328]. Credibility: Oxford Ionics' physics claims have held and improved on schedule; IonQ's scale promises have not — the 2020 roadmap's 4,000 qubits by 2026 missed by roughly 40× — so read fidelity commitments as credible and qubit-count dates as aspirational.

Strategic reading. If the electronic gate scales, IonQ converts a physics lead into a manufacturing lead and the optical supply chain for ions loses its strongest customer class; Quantinuum's advantage narrows to systems engineering and error correction rather than gate quality. If it stalls at a few tens of ions, the record becomes a laboratory curiosity and laser gates with integrated photonics win on demonstrated width. Bargaining power sits with the platform vendor: nothing in the chain is scarce except packaging know-how, and IonQ has internalised the fab.

Confirm-or-demote milestones for 12–24 months: a device above ~30 electronic-gate qubits with published two-qubit fidelity, gate time and crosstalk (absent by end-2027, demote); IonQ's 256-qubit system commissioned in H1 2027 near 99.99%; any independent replication above 99.9%; a 2D trap running electronic gates with published heating rates. Best case by 2029: chip-trap machines of a few thousand ions, laser hardware reduced to cooling and readout, gate error near 10⁻⁴, error correction limited by transport rather than gates. Worst case: fidelity degrades by an order of magnitude once hundreds of microwave channels share a die, and the platform reverts to laser gates for addressing.

Open questions: does the microwave gradient survive dense 2D routing without unacceptable crosstalk and dissipation? How much of the residual 8.4×10⁻⁵ is coherent, and what does that do to Λ? Does SkyWater's process yield trap chips at volume, or was the acquisition supply security rather than capability?