Diamond growth / implantation (NV, SiV, SnV) fab_diamond

Plasma CVD grows single-crystal diamond on a seed; nitrogen, silicon or tin is implanted; a high-temperature anneal mobilises vacancies that bind the impurity into a colour centre; the optical structure is then cut from the bulk. That last step is the defining constraint: there is no diamond-on-insulator wafer and no sacrificial layer, so cavities are released by undercut etching of the same crystal that hosts the defect. Implantation-based fabrication matured around 2010; QuTech's 2026 SnV cavity study sets the benchmark Dfact.
Attributes: engineered placement of a natural defect, no mobility and no control step, Pauli error once fabricated, diamond fabrication with no CMOS analogue.

Three independent things must go right at one site. The ion must stop where intended: straggle is tens of nanometres, an order worse than STM donor placement. It must convert into an optically good centre — only a fraction take the wanted charge state, and residual damage broadens the line. Then the etched cavity must put its field maximum on that centre: cooperativity goes as g²/κγ, with g set by position inside a mode a few hundred nanometres across. The three partial yields multiply, and none is published over a whole chip: of 327 cavities characterised at room temperature, 9 were cooled, 7 of them held a coupled SnV, and the two measured in full reached coherent cooperativity 8.3 and 1.6 Dfact. Only deterministic single-ion implantation with event detection, or in-growth delta doping with registration, moves that floor; neither exists at device scale.

Dominant term: device yield. The fibre microcavity is a fabrication answer as much as an optical one: the resonator sits outside the crystal, removing the undercut-etch lottery.

The 327-cavity SnV study, first reported in a news item [362], is published in Physical Review X fact: its 327 cavities were characterised at room temperature, only 9 were cooled, and the two emitter–cavity devices measured in full exceeded cooperativity one; the result is single-source and unreplicated. Its ¹²⁰Sn implant at 350 keV reaches a depth of 88 ± 16 nm fact, a spread of tens of nanometres. Element Six's lead as the diamond source of most NV-centre companies rests on a secondary survey [364]. Not published: the fraction of the 327 cavities above cooperativity one, so device yield is unknown; the lateral implantation straggle and an ion-to-usable-centre conversion yield; a dated capacity, revenue or investment figure for Element Six's quantum segment; and a cost per device, wafer count or throughput for any diamond quantum process.

Element Six is the main merchant supplier, selling plates by catalogue; its DNV-B1 grade (2020-06-15) targets NV ensembles, while single-defect work needs electronic-grade single crystal C[361]. Its growth capacity sits in the UK and California C[361]; two smaller sources are Diatope, an Ulm University spin-out (2021) selling engineered NV diamond, and Quantum Brilliance's quantum-diamond foundry in Melbourne, opened in 2025 to make quantum-grade diamond at scale P[364]. Implantation runs on general-purpose accelerators; ¹²C-enriched growth costs more. Nothing is on a 300 mm path: millimetre-scale plates processed individually, with no published wafer count, cost or throughput. Export exposure is not nil: since 2022-08-15 the US Export Control Classification Number (ECCN) 3C005.a names diamond semiconductor substrates, ingots and boules above 10⁴ Ω·cm, and 3C006 an epitaxial diamond layer on such a substrate fact; whether an electronic-grade quantum plate counts as a semiconductor substrate has not been ruled on, and no ECCN names colour centres. Burden passed upward: a laser and a detector per site.

Provides the host crystal colour-centre spins and their gates require, hence the defect-node architecture. It is the counterpart of STM hydrogen-resist lithography, not a substitute: implantation buys area throughput at an order of magnitude of placement precision, and neither route publishes a yield distribution. Verification: the 327-cavity study is one institution's, announced in a news release P[362] and peer-reviewed in Physical Review X Dfact, with nothing to replicate it against.

Who.
| Organisation | Role | Country | What exactly they do | Evidence |
|---|---|---|---|---|
| QuTech | research | Netherlands | SnV nanocavity fabrication and cryogenic characterisation | Dfact |
| Element Six | supplier | UK | Merchant CVD diamond plates | C[361] |
| Diatope | supplier | Germany | Engineered NV diamond; Ulm University spin-out (2021) | P[364] |
| Harvard | research | USA | Implanted SiV nanophotonics | D[209] |
| Quantum Brilliance | developer | Australia | Room-temperature units; quantum-diamond foundry in Melbourne (2025) | P[364] |
| QuantumDiamonds | developer | Germany | NV microscopy, Munich | P[364] |

Money. 2026-07 · QuantumDiamonds · grant and equity · EUR 91 M, EUR 76 M of it EU Chips Act · financing a EUR 152 M Munich facility · closed P[364]. 2025-01 · Quantum Brilliance · Series A · USD 20 M · ~USD 58 M cumulative · closed P[364]. No QBI stage names diamond manufacturing.

Market & supply chain. One dominant substrate supplier is the concentration risk, its two alternatives dating only from 2021 and 2025; accelerators and etch tools are generic. Unit economics are unpublished. Pays into G6 and sensing.

IP & standards. No dated patent family from a named database as of 4 Sep 2026; Element Six's DNV grades are a de facto benchmark.

Roadmaps & track record. QuTech (modular-computing programme · on schedule) P[362]. QuantumDiamonds (Munich facility, 2026-07 · too new to judge) P[364]. Quantum Brilliance (units at three laboratories · delivered, dates unstated) P[364]. No actor publishes a dated yield target.

Strategic reading. Element Six wins in every scenario: it sells substrate to actors who compete with each other, not it. The fibre microcavity is the quiet threat — a resonator outside the crystal removes most of the nanofabrication problem.

Confirm/demote (12–24 months): deterministic single-ion implantation with event detection, or a published chip-wide fraction of cavities above cooperativity one, confirms; two more years without either demotes this to a research process. Best case 2029: chip-scale arrays with tens of usable nodes. Worst case: every node stays hand-selected. Open: (1) can implantation precision approach one nanometre; (2) do Diatope or Quantum Brilliance's foundry grow into a second source at Element Six's scale; (3) does external-cavity coupling displace monolithic nanophotonics.