A Quantum Computing Material That Already Grows in Chip Factories

The leading solid-state spin qubit in quantum computing research, the nitrogen-vacancy center in diamond, has a manufacturing problem. Diamond does not grow easily at wafer scale, and it resists the lithography and deposition steps the chip industry has spent sixty years perfecting. A multi-institutional team now says it has identified an alternative: a specific atomic-scale flaw in zinc oxide, the transparent semiconductor already produced in volume for LEDs, touch sensors, and solar cells.

Researchers from Sungkyunkwan University (SKKU), the University of Wisconsin–Madison, and the University of Washington report in a study in PRX Quantum that a defect in which a molybdenum atom replaces a zinc atom next to a missing oxygen atom behaves as a viable spin qubit, the basic memory and calculation unit of a future quantum computer. The work is computational, not a measured device, but the numbers are concrete: under magnetic noise, the defect shows electron spin coherence of about four milliseconds, with sharp, well-defined visible-light emission at room temperature.

Those two properties are the load-bearing ones. Coherence is how long a qubit holds its quantum state before noise scrambles it. Sharp light emission is what lets a future device read and write that state with a laser. Both also work at room temperature, in contrast with platforms that need to be chilled near absolute zero. The diamond NV center shows all of these qualities, and is also trapped in a host material the semiconductor industry cannot process at scale. Zinc oxide is the opposite: a chip-fab-friendly material with a thin-film toolkit that already exists.

SKKU's Hosung Seo led the study and pointed to a specific structural feature. The defect sits in what physicists call a "magnetically quiet" host. Zinc oxide's natural mix of zinc and oxygen contains almost no nuclear spins, the tiny magnetic moments inside atomic nuclei that normally add noise to a qubit's environment. Fewer background spins means a longer-lived quantum state. The team also reports that the Huang–Rhys factor, a measure of how much a defect distorts its surrounding crystal when it absorbs light, is far smaller for this defect than for any previously known zinc-oxide defect. A small Huang–Rhys factor means sharper emission lines, which is what makes optical readout and spin-photon coupling workable.

The collaboration added two ingredients a single lab could not have assembled. At UW–Madison, the Ping group ran the first-principles supercomputer simulations that screened candidate defects and predicted the coherence and optical properties. At the University of Washington, the Fu group (ECE profile) contributed defect characterization expertise developed on other wide-bandgap semiconductors. The defect structure itself emerged from that pipeline rather than from a measured device.

The manufacturing-pathway argument is the part the wire coverage will miss. Quantum computing has spent two decades chasing host materials that physicists can measure cleanly, and the field's reference design, the diamond NV center, is one of those. It also has a ceiling: a few-millimeter diamond sample is the practical upper bound, and integrating NV centers with the lithography, etching, and thin-film deposition of a real fab line is a research project in itself. Zinc oxide, by contrast, is grown on six-inch and eight-inch wafers today, and the deposition tooling sits in commercial foundries. A defect in a material the industry already masters is a different kind of bet than a defect in a material the industry has to learn.

A working spin qubit needs more than long coherence and sharp light. It needs a way to place single defects at known locations, address them individually, and read them out with high enough fidelity to run error correction. The paper does not address single-shot readout, the precise placement problem, or reproducibility from wafer to wafer. Those are the questions that decide whether a candidate material becomes a platform. Secondary coverage has cast the result as a step toward single-shot readout, but the underlying paper stops at the simulation stage and presents the work as identifying a candidate, not building a device.

The next milestones are not in simulation. They are in crystal growth: whether the molybdenum-oxygen-vacancy complex can be produced in actual zinc-oxide wafers with the predicted properties intact, and whether the defect's behavior survives contact with the surfaces, dopants, and interfaces a real device would impose. A measurement of room-temperature coherence in a grown crystal would move the result from candidate to platform, and the multi-institutional pipeline that produced the simulation is positioned to run that experiment.