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Colour-centre / defect spin (NV, SiV, SnV, T centre) defect

An optically addressable point-defect spin in diamond or silicon whose electron couples coherently to a photon, making it a network node with a small nuclear register rather than a processor qubit.

Colour-centre / defect spin (NV, SiV, SnV, T centre)

defect · layer 1 Qubit carrier · demonstrated · since 2004
Open on the map

Optically addressable spin in a solid host; network node with spin–photon interface rather than a processor qubit.

Brief →

Key references

[209] C. M. Knaut et al., “Entanglement of nanophotonic quantum memory nodes in a telecom networ… · 2024
[359] J. Fischer et al., “Spin-photon correlations from a Purcell-enhanced diamond nitrogen-vaca… · 2025
[360] M. Iuliano et al., “Unconditionally teleported quantum gates between remote solid-state qu… · 2026
[208] M. Swayne, “Fujitsu And QuTech Realize High-Precision Quantum Gates,” The Quantum Insider,… · 2025
[364] M. U. Rehman, “Top Diamond NV-Centre Quantum Computing Companies in 2026,” The Quantum Ins… · 2026

Design space — attributes

(a) carrier affinity
intermediate / carrier-agnostic
(b) time · entangling
1.0 µs · deterministic
(c) readout
fluorescence (PMT/SNSPD) · 100 µs · non-destructive · mid-circuit
(d) mobility
flying qubits (photons)
(e) control
optical @ room temperature
(f) error structure
stochastic Pauli, loss (erasure)
(g) manufacturing
diamond growth / implantation

Evaluation space — dated attributes

NV gate errors (GST) → < 0.1% [P] — press release only, no primary paper
defines: error channel · 2025-03 · source

QuTech/Fujitsu, Harvard, Photonic Inc (T centres), Quantum Brilliance. Element Six's DNV-B1 is an NV-*ensemble* sensing grade, not a single-defect node substrate.

Standard records

T1 relaxation → 3600 s · best
NV electron spin in a 10-qubit diamond register (4 K): T1 = 3.6(3)e3 s, i.e. > 1 hour · 2019-05 · source [D] ⓘ
T2 coherence (echo/DD) → 600 ms · best
NV electron spin: T2 ~ 0.6 s (580 ms) with 8192-pulse CPMG at 77 K in isotopically pure diamond · 2013-04 · source [D] ⓘ
1Q gate time → 997 µs · typical
Delft NV register: nuclear-spin 1Q gates via electron-controlled DD take 419-2,371 us; electron MW Rabi is 14 MHz · 2019-05 · source [D] ⓘ
idle / memory error per round → not published · typical
No NV/SiV QEC round with a published per-round idle error · 2019-05 · source [D] ⓘ

Actors & goals — annotations

Colour-centre spins — network nodes (NV/SiV/T) — QuTech/Fujitsu, Harvard, Photonic Inc, Quantum Brilliance · G6

Edges

needs: Diamond growth / implantation (NV, SiV, SnV)·
needed by: Microwave / optical spin gates (defect centres, 1Q spins)°, Fluorescence state detection (ions, defects)°, Spin–photon solid-state link (SiV, NV, T centre), Single-spin (Loss–DiVincenzo) / nuclear-spin encoding°
° one of several that would do · the usual route, not a strict need

Used by 5 machines (5 primary · 0 alternate)

↗ its register card · paper / product / press: links that name the machine (attribution checked on 20 Sep 2026)

Pictures

Every picture carries the story of what it shows and its credit line.

File:NV center in solid immersion lens.jpg
A two-part paper figure panel: a scanning electron micrograph of a dome-shaped solid immersion lens etched into diamond (1 µm scale bar), and a photoluminescence map showing a single NV centre at its middle, in photons per millisecond. It is by David A. Hopper, Henry J. Shulevitz and Lee C. Bassett (2018). The nitrogen-vacancy centre is a defect whose spin serves as a qubit; the lens, with the NV at its focus, directs its photons out of the diamond towards a detector, a setup often used for entanglement experiments. “NV center in solid immersion lens” by David A. Hopper, Henry J. Shulevitz, Lee C. Bassett, commons.wikimedia.org/wiki/File:NV_center_in_solid_immersion…, CC BY 4.0 (creativecommons.org/licenses/by/4.0/)
Fig. 1 — Figure 1: a. Experimental setup for probing the collective emission of atom-like emitter arrays. b. The SiV centre is an atom-like emitter system wh…
A three-panel drawing: an optical set-up exciting a diamond sample in a 4 K chamber and imaging its emission, an energy-level scheme of the silicon-vacancy (SiV) centre with four transitions near 737 nm, and a square array of emitter sites. It is Fig. 1 of "Collective emission of subwavelengths atom-like emitter arrays in the presence of inhomogeneous broadening" by Uri Israeli, Rivka Bekenstein and colleagues. SiV centres behave like atoms; closely spaced sites can emit collectively, and the spread of individual emitter frequencies limits that effect. “Fig. 1 — Figure 1: a. Experimental setup for probing the collective emission of atom-like emitter arrays. b. The SiV centre is an atom-like emitter system whose ground…” by Uri Israeli et al., arxiv.org/abs/2606.07458, CC BY 4.0 (creativecommons.org/licenses/by/4.0/)
File:Si-V diamond PL map.jpg
Two false-colour confocal photoluminescence maps of a diamond: a 5 by 5 micrometre surface scan with about twenty bright spots, and a depth scan below it showing emitters roughly 1.5 micrometres under the surface (yellow dashed line). From a 2015 work by Yan Liu, Gengxu Chen, Fedor Jelezko and co-authors; the silicon-vacancy centres were created by implanting silicon ions. Each isolated spot is a single optically active defect, the kind of colour centre used as a spin qubit or photon source; notice how the depth scan locates one circled emitter. “Si-V diamond PL map” by Yan Liu et al., commons.wikimedia.org/wiki/File:Si-V_diamond_PL_map.jpg, CC BY 4.0 (creativecommons.org/licenses/by/4.0/)
defect · layer 1 Qubit carrier · centrality 4.2 · demonstrated · since 2004 · updated 2026-09-30

Colour-centre / defect spin (NV, SiV, SnV, T centre)

An optically addressable point-defect spin in diamond or silicon whose electron couples coherently to a photon, making it a network node with a small nuclear register rather than a processor qubit.

Verdict. The best spin–photon interface in solid state, but link rates of millihertz to hertz keep every actor in networking and sensing; no defect platform has a logical qubit or a dated processor roadmap.

Key references

Λ = error-suppression factor per code-distance step; QBI = DARPA Quantum Benchmarking Initiative (Stage A concept → B R&D plan → C government V&V); G1–G7 = the report's goal classes (see Actors & economics).

Identity & lineage

A point defect — nitrogen-vacancy, the group-IV silicon- and tin-vacancies in diamond, or silicon's T centre — read by fluorescence and entangled with an emitted photon, nearby nuclei as a small memory. Coherent single-spin control dates to 2004. The split that matters is symmetry: NV lacks inversion symmetry and so diffuses spectrally; SiV and SnV are inversion-symmetric.
Attributes: natural defect, engineered placement, static host with a flying photon, ~1 µs gates; fluorescence readout ~100 µs, non-destructive and mid-circuit; optical plus microwave control; Pauli and loss error.

Physics & limits

Everything rests on the chance an excited defect puts a usable photon into fibre. NV emits a few per cent into its zero-phonon line and diffuses spectrally under charge switching, so a cavity is mandatory — Delft's fibre microcavity took resonant collection from ~0.05% to ~0.5% at echo coherence above 100 µs D[359]. Group-IV centres fix the linewidth by symmetry but pay in temperature: SiV below 100 mK, SnV nearer 1–4 K. Heralded rate goes as efficiency squared — 10× optical gain is 100× in rate; link rate, not gate error, is the figure of merit. Loss is heralded, entering the code as erasure — the one structural edge over dot and donor spins.

Engineering state of the art

table
year figure who tag+key
2024-05-15 SiV nodes at 0.69(7) over 35 km of deployed fibre, 17 dB loss Harvard D[209]
2025-11-27 fibre-microcavity photon collection ~0.05% → ~0.5% QuTech D[359]
2026-05-26 unconditional teleported CNOT between cryostats, 63(4)%; GHZ 64(4)% QuTech D[360]

Local gates are not the problem: Fujitsu and QuTech report NV errors below 0.1% by gate-set tomography P[208]. Collection dominates; no defect platform has a logical qubit.

The Fujitsu/QuTech "below 0.1%" NV gate error comes only from a joint press release relayed by trade press [208]. Element Six's lead as the diamond source of most NV-centre companies rests on a secondary survey [364]. Photonic Inc.'s T-centre tCNOT is post-selected [363]. Not published: a peer-reviewed paper with gate-set-tomography error bars for the Fujitsu/QuTech figure; Element Six's capacity, revenue or quantum-segment figures; a journal paper on Photonic Inc.'s T-centre work, as of 2026-09-04, and a gate fidelity for its tCNOT; and the dates of Quantum Brilliance's three deployments at Oak Ridge, Fraunhofer IAF and Pawsey [364].

Manufacturing, materials & supply chain

Hosts: CVD diamond with implanted defects, or defect-engineered silicon for T centres. Element Six is the main merchant supplier, selling DNV-B1 (2020-06-15) by catalogue — but that grade targets NV ensembles C[361]; single-defect nodes need electronic-grade plates. Two smaller sources exist: Diatope, an Ulm University spin-out (2021) selling engineered NV diamond, and Quantum Brilliance's quantum-diamond foundry in Melbourne (2025) P[364]. Device yield is the missing number: QuTech's SnV study P[362] characterised 327 nanocavities at room temperature, found coupled centres in 7 of the 9 it cooled and measured two above cooperativity one, with no chip-wide fraction Dfact. Optical I/O does not multiplex — each node needs its own resonant laser, microwave line, detector and fast feed-forward D[360], so burden scales per node and 10³ nodes is nobody's target. Export control does name diamond: ECCN 3C005.a has covered diamond semiconductor substrates and their ingots above 10⁴ Ω·cm since 2022-08-15, and 3C006 such substrates carrying an epitaxial layer fact; whether a quantum-grade plate counts as a semiconductor substrate is the open question.

Role in the stack

Architecture: colour-centre spins — network nodes (NV/SiV/T), as its primary carrier. The register lists 5 machines using it, among them SaxonQ's QC2026 Dual Core, Quantum Brilliance's Quoll / QB-QDK 2.0 and Fujitsu's Diamond-spin quantum computer prototype. Requires diamond growth or implantation; provides spin gating, fluorescence readout and the spin–photon link consumed upstream. The derived clock is transport-dominated by six to nine orders: ~1 µs gates against heralded links at 7.5 mHz (T centre, 40 m) to ~1 Hz (SiV, 20 m) P[363]D[209]. Two teleported-CNOT (tCNOT) claims coexist, one on T centres and one on NV, and both are right. Photonic Inc.'s T-centre tCNOT between cryostats was post-selected, no feed-forward and no gate fidelity, at Bell 0.60(8) P[363]; QuTech's NV gate is unconditional at 63(4)% D[360]. Only the second is a gate.

Actors & economics

Who.
| Organisation | Role | Country | What exactly they do | Evidence |
|---|---|---|---|---|
| QuTech | developer | Netherlands | NV cavities, SnV nanocavities, teleported CNOT | D[359], [360], fact |
| Photonic Inc. | developer | Canada | Silicon T-centre modules | P[363] |
| Harvard | research | USA | SiV nodes over urban fibre | D[209] |
| Element Six | supplier | UK | Merchant CVD diamond | C[361] |
| Quantum Brilliance | developer | Australia | Room-temperature diamond units | P[364] |

Money. 2025-11-06 · Photonic Inc. · QBI Stage B · up to USD 15 M · DARPA · awarded fact. 2026-05-12 · Photonic Inc. · equity · USD 200 M at USD 2 B · Microsoft returning · USD 350 M cumulative · closed P[186]. 2026-07 · QuantumDiamonds · EUR 91 M, EUR 76 M of it EU Chips Act · closed P[364].

Market & supply chain. Two concentration points: substrate, where Element Six dominates and its two alternatives date only from 2021 and 2025, and a thin detector base for readout. Sensing revenue funds the field; nothing here is bought against G3 or G4.

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. Photonic Inc. (2023-11 · fault-tolerant distributed computing "within five years" · unmet; its published rate is seven orders below its own ~200 kHz target) P[364]. Quantum Brilliance ships rather than promises; QuTech is on schedule.

Strategic reading. Defect spins win only if distributed modules bind before monolithic fault tolerance does — then every platform buys this interface instead of building it. Element Six holds supplier power because it never competes on qubit design.

Outlook & open questions

Confirm/demote (12–24 months): an unconditional inter-node gate above 90%, or a link above 1 kHz, confirms the thesis; two more years at hertz rates demotes it to sensing. Best case 2029: a multi-node repeater segment with error detection. Worst case: laboratory links only. Open: (1) does anyone publish a chip-wide SnV device yield; (2) do Diatope or Quantum Brilliance's foundry grow into a second source at Element Six's scale; (3) can T-centre rates close on SiV.

References
  1. [186] M. Abdel-Kareem, “Photonic Inc. Reaches $2B Valuation with $200M Final Close,” Quantum Computing Report, May 12, 2026. [Online]. Available: https://quantumcomputingreport.com/photonic-inc-reaches-2b-valuation-with-200m-final-close/ P
  2. [208] M. Swayne, “Fujitsu And QuTech Realize High-Precision Quantum Gates,” The Quantum Insider, Mar. 28, 2025. [Online]. Available: https://thequantuminsider.com/2025/03/28/fujitsu-and-qutech-realize-high-precision-quantum-gates/ P
  3. [209] C. M. Knaut et al., “Entanglement of nanophotonic quantum memory nodes in a telecom network,” Nature, vol. 629, no. 8012, pp. 573–578, May 2024, doi: 10.1038/s41586-024-07252-z. D
  4. [359] J. Fischer et al., “Spin-photon correlations from a Purcell-enhanced diamond nitrogen-vacancy center coupled to an open microcavity,” Nat. Commun., vol. 16, no. 1, Art. no. 11680, Nov. 2025, doi: 10.1038/s41467-025-66722-8. D
  5. [360] M. Iuliano et al., “Unconditionally teleported quantum gates between remote solid-state qubit registers,” Nat. Commun., vol. 17, no. 1, Art. no. 4694, May 2026, doi: 10.1038/s41467-026-72818-6. D
  6. [361] Element Six, “Element Six launches DNV-B1™ – its first commercially-available, general-purpose quantum grade diamond,” Jun. 15, 2020. [Online]. Available: https://www.e6.com/en/about/news/dnv-b1-launch C
  7. [362] QuTech, “Coherent coupling of diamond colour centre to a nanocavity,” Jun. 25, 2026. [Online]. Available: https://qutech.nl/2026/06/25/a-step-toward-faster-quantum-networks/ P
  8. [363] F. Afzal et al., “Distributed Quantum Computing in Silicon,” arXiv:2406.01704, Jun. 2024. P
  9. [364] M. U. Rehman, “Top Diamond NV-Centre Quantum Computing Companies in 2026,” The Quantum Insider, Jul. 10, 2026. [Online]. Available: https://thequantuminsider.com/2026/07/10/8-quantum-computing-companies-working-with-nv-centre-in-diamond-technology/ P