# Can Zinc Oxide Replace Diamond for Room-Temperature Spin Qubits?

A computational study published in *PRX Quantum* says yes — at least in principle. A team led by Professor Hosung Seo at Sungkyunkwan University (SKKU), working with collaborators at the University of Wisconsin–Madison and the University of Washington, has identified a molybdenum-oxygen-vacancy complex — written as (Mo_Zn v_O)²⁺ — in zinc oxide (ZnO) as an optically addressable, deep-level spin-triplet defect capable of functioning as a high-fidelity spin qubit at room temperature. The paper, titled *Deep Spin Defects in Zinc Oxide for High-Fidelity Single-Shot Readout*, is open-access in *PRX Quantum*.

This is the first time a room-temperature-stable spin qubit has been identified in ZnO. The significance is structural, not just physical: ZnO is already embedded in global semiconductor manufacturing, can be grown as ultra-high-purity, large-area wafers via Molecular Beam Epitaxy (MBE), and — critically — its oxygen isotopes are reported to be 99.7% free of nuclear spin. That last figure matters enormously for [decoherence](https://quantumintel.tech/glossary/decoherence): a magnetically quiet host lattice is one of the hardest engineering constraints to satisfy in solid-state qubit design.

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## Why the NV Center in Diamond Has a Scalability Problem

The [NV Center](https://quantumintel.tech/glossary/nv-center) in diamond remains the reference architecture for solid-state spin qubits. It operates at room temperature and has demonstrated [coherence time](https://quantumintel.tech/glossary/coherence-time) records that make it attractive for quantum sensing and quantum networking. But diamond carries two structural liabilities that the industry has never fully solved.

First, growing diamond as large-area single crystals is notoriously difficult — yields are low, substrate sizes are constrained, and the material science is expensive. Second, and more fundamentally, diamond is incompatible with standard CMOS manufacturing. You cannot run a diamond wafer through a silicon fab. Any future quantum network that requires millions of integrated spin-photon interfaces — the kind of density needed for a practical quantum repeater infrastructure — cannot be built on diamond at scale without an entirely parallel and costly fabrication ecosystem.

ZnO sidesteps both problems. It grows via MBE on large-area substrates, it fits within existing oxide semiconductor process flows, and the nuclear spin background is exceptionally clean. The SKKU team's argument is not that ZnO is better than diamond in every metric today — it's that ZnO provides a credible path to semiconductor-foundry-compatible spin qubits, which diamond categorically cannot offer.

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## The Defect: What Makes (Mo_Zn v_O)²⁺ Work

Previous work on spin defects in ZnO focused on shallow donor defects such as Indium or Gallium substitutions. The source material notes that these defects carry a fundamental limitation: low binding energy restricts their operation to cryogenic temperatures and confines their optical emission to the UV spectrum. Neither property is useful for room-temperature quantum hardware or for fiber-compatible quantum networking.

The SKKU team took a different approach — a systematic, periodic-table-wide computational screen of substitutional defects in ZnO using Density Functional Theory (DFT) and Green's function (GW) simulations. The molybdenum substitution emerged as the candidate. The resulting (Mo_Zn v_O)²⁺ complex — a molybdenum atom on a zinc site, paired with an adjacent oxygen vacancy, carrying a 2+ charge state — exhibits what the paper characterizes as localized spin-triplet ground states with superior thermal stability relative to the shallow donor alternatives.

The paper identifies three critical physical properties the defect must satisfy to serve as a viable quantum light source and spin-photon interface, though the source material does not enumerate all three explicitly. What is stated: the complex is optically addressable (meaning spin states can be initialized and read out via light), it is a deep-level defect (thermally stable at room temperature), and it supports spin-triplet ground states (the electronic structure required for single-shot spin readout schemes analogous to those used with NV centers).

The theoretical methodology — DFT combined with GW corrections — is the established computational toolkit for predicting defect energy levels and optical transitions in wide-bandgap semiconductors. This is not a speculative ab initio guess; it is the same class of calculation that correctly predicted NV center properties before experimental confirmation. That does not guarantee experimental realization, but it sets a credible prior.

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## The Gap Between Theory and a Working Qubit

This result is entirely computational. No ZnO device with a (Mo_Zn v_O)²⁺ defect has been fabricated, no T1 or T2 times have been measured, and no single-shot readout fidelity has been demonstrated experimentally. That is not a criticism of the paper — theory-first discovery is the appropriate workflow for defect engineering — but investors and enterprise buyers should calibrate accordingly.

The path from a DFT prediction to a working spin-qubit device in a fab-compatible material involves at minimum: controlled molybdenum implantation at the single-defect level, optical characterization of the zero-phonon line and spin-state contrast, pulsed ESR or optically detected magnetic resonance (ODMR) spectroscopy to extract T1/T2, and eventually [gate fidelity](https://quantumintel.tech/glossary/gate-fidelity) benchmarking. Each step can take years and each can reveal that the predicted properties don't fully materialize in real material with real defect densities and strain environments.

The ZnO community also has to contend with surface chemistry: ZnO is chemically reactive compared to diamond, and surface states can degrade spin [coherence time](https://quantumintel.tech/glossary/coherence-time) in near-surface defects that need to be close to interfaces for sensing or photonic coupling.

None of this invalidates the result. It contextualizes the timeline.

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## Industry Implications: Sensing, Networking, and the Foundry Question

The application space the SKKU team targets — integrated quantum networks and ultra-sensitive solid-state quantum sensors — is precisely where the foundry compatibility argument has maximum leverage. Quantum sensing with spin defects does not require fault-tolerant error correction or millions of entangled [logical qubits](https://quantumintel.tech/glossary/logical-qubit). It requires a single, high-coherence spin defect near a surface or integrated into a photonic structure, operating reliably without a [dilution refrigerator](https://quantumintel.tech/glossary/dilution-refrigerator). That is a commercially realistic near-term target.

For quantum networking, the spin-photon interface quality depends on the brightness, coherence, and wavelength of the optical transition — none of which have been measured yet for (Mo_Zn v_O)²⁺. If the zero-phonon line falls in a telecom-compatible window, that would be a significant practical advantage for fiber-based networks. The source material does not specify the predicted optical emission wavelength, so this remains an open question.

The broader industry trajectory here is a gradual diversification away from diamond as the only room-temperature solid-state spin qubit platform. Silicon carbide (SiC) has been the most actively pursued alternative, with groups at multiple institutions demonstrating optically addressable spin defects at room temperature. ZnO now enters that competition with the specific advantage of existing large-scale commercial infrastructure and an exceptionally clean nuclear spin environment. Whether it can compete with SiC on optical properties and fabrication maturity will take several experimental years to determine.

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## Key Takeaways

- SKKU, University of Wisconsin–Madison, and University of Washington have **computationally identified** the (Mo_Zn v_O)²⁺ defect in ZnO as a room-temperature spin qubit candidate, published in *PRX Quantum*.
- ZnO is the first wide-bandgap semiconductor **already integrated into CMOS-compatible manufacturing** to host a predicted room-temperature spin-triplet defect.
- The host material's oxygen isotopes are reported to be **99.7% free of nuclear spin**, reducing the primary decoherence noise source.
- The result is **entirely theoretical** — no T1/T2 measurements, no fabricated device, no gate fidelity data exist yet.
- Primary application targets are **quantum sensing** and **quantum networking** spin-photon interfaces, not gate-based computing.
- This positions ZnO as a potential competitor to **silicon carbide** in the room-temperature solid-state spin qubit space, with a fabrication-compatibility argument that diamond cannot make.

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## Frequently Asked Questions

**What is the (Mo_Zn v_O)²⁺ defect in zinc oxide?**
It is a molybdenum atom substituted onto a zinc lattice site, paired with an adjacent oxygen vacancy, in a 2+ charge state. The SKKU-led team's calculations predict it forms a spin-triplet ground state that can be optically addressed — the key properties needed for a spin qubit — and that it remains thermally stable at room temperature.

**Why is ZnO considered better than diamond for scalable spin qubits?**
Diamond cannot be grown as large-area single crystals economically and is incompatible with standard CMOS fabrication. ZnO can be deposited via MBE on large-area wafers and fits within existing oxide semiconductor process flows. Additionally, ZnO's oxygen isotopes are reported to be 99.7% free of nuclear spin, meaning the host lattice produces minimal magnetic noise that would degrade qubit coherence.

**Has this spin qubit been experimentally demonstrated?**
No. The identification is computational, using Density Functional Theory and Green's function (GW) simulations. No device has been fabricated, and no experimental measurements of coherence time, optical emission, or spin readout fidelity have been reported for this defect.

**How does this compare to NV centers in diamond?**
NV centers in diamond are the established benchmark for room-temperature solid-state spin qubits, with extensive experimental characterization. The ZnO molybdenum defect is a theoretical prediction that addresses diamond's scalability and CMOS-compatibility limitations, but lacks any experimental validation to date. The two systems cannot be directly compared on performance metrics until ZnO device data exists.

**What applications would ZnO spin qubits enable?**
The SKKU team specifically targets integrated quantum networks (where spin-photon interfaces at room temperature are needed) and ultra-sensitive solid-state quantum sensors. These applications require room-temperature operation and, ideally, semiconductor foundry compatibility — both of which ZnO can potentially provide.

**How long until a working ZnO spin qubit device could exist?**
The source material does not project a timeline. Based on the state of analogous programs — such as silicon carbide spin defect development — moving from a strong theoretical prediction to experimental characterization of T1/T2 and optical properties typically takes several years of materials and device work.