Ultraviolet laser pulses engineer diamond defects selectively, leaving quantum qubits intact

When we think about a diamond, we often think about a material whose value comes from its perfection. In my research, however, I am interested in something almost opposite: the tiny imperfections inside diamonds. These atomic-scale defects can give diamonds new optical and electronic properties, and some of them can serve as quantum systems. The challenge is learning how to control these defects without disturbing the others.

This problem becomes particularly important for quantum technologies. A nitrogen-vacancy (NV) center, for example, is a defect formed when a nitrogen atom and a neighboring vacancy occur in the diamond lattice. NV centers can be used as quantum bits, or qubits, and as highly sensitive sensors of magnetic and electric fields. But creating or modifying one type of defect can also affect other defects nearby. If we want to build useful devices from diamond, we need ways to control individual defect populations more selectively.

Our work, now published in the journal Diamond and Related Materials, explored whether ultraviolet laser pulses could provide that control.

Testing localized ultraviolet pulses

I used a single-crystal chemical vapor deposition (CVD) diamond and irradiated localized regions of the crystal with 266-nanometer ultraviolet laser pulses. The pulses were only a few nanoseconds long, allowing the laser energy to be delivered to a very small region of the material. Rather than heating the entire diamond, the goal was to investigate whether this localized optical excitation could modify particular defects within the lattice.

Before exposing the diamond to the laser, we first needed to understand what was already present. This became an important part of the study because it is difficult to claim that a defect was created by a laser if it was already present in the starting material.

We therefore characterized the pristine diamond using confocal photoluminescence spectroscopy, ultraviolet-visible absorption spectroscopy and Fourier-transform infrared spectroscopy. The confocal measurements established the initial optical defect landscape, while the absorption and infrared measurements provided additional information about the optical transparency and impurity content of the starting crystal. In particular, the measurements indicated that the low-nitrogen CVD diamond contained a very small concentration of substitutional nitrogen compared with nitrogen-rich diamond materials.

New emissions, largely unchanged NV centers

We then compared the optical response of the diamond before and after laser irradiation. The most interesting change appeared in the photoluminescence spectrum. After irradiation, a previously absent emission near 563 nanometers appeared in the laser-exposed regions. A second feature near 579 nanometers appeared alongside it. These emissions have been associated in previous studies with defect configurations related to carbon self-interstitials—carbon atoms occupying positions in the diamond lattice that are different from their normal lattice sites.

What made the observation particularly interesting was not simply that new optical defects appeared. It was what happened to the defects that were already there.

The diamond already contained NV centers before irradiation. After laser treatment, their optical signals remained largely unchanged compared with the untreated regions. In other words, the laser was capable of producing a measurable change in one part of the defect landscape without producing a comparable change in the existing NV-center population.

I think this distinction is important. We are not reporting that the 563-nanometer or 579-nanometer centers are newly demonstrated qubits. Rather, the significance of the experiment is in the ability to manipulate a particular defect population while preserving a preexisting quantum-relevant defect population.

Defect transformations remain partly unresolved

We also observed that the newly generated 563-nanometer emission did not simply continue increasing with increasing laser exposure. Under continued irradiation, the signal could decrease after reaching a maximum. This behavior suggests that the laser is not merely creating defects in a one-way process. Instead, the optical excitation can drive defect transformations in which particular configurations are generated and subsequently modified.

The exact atomic-scale mechanism remains an open question. Our results are consistent with a picture in which sub-bandgap ultraviolet photons interact with defect-associated electronic states, producing localized electronic excitation and subsequent energy transfer to the surrounding lattice. Such processes could promote rearrangement of carbon atoms near existing defect sites. However, establishing the complete microscopic pathway will require further experiments.

That limitation is important because diamond contains many different defect configurations, and their optical signatures alone do not always reveal their complete atomic structures. The 563-nanometer and 579-nanometer emissions, for example, have been associated with self-interstitial-related defects, but the precise atomic configuration responsible for the observed centers has not been established by our measurements.

Toward a designed defect landscape

What we have demonstrated is therefore a materials-engineering concept: nanosecond ultraviolet laser irradiation can be used to selectively modify the optical defect structure of single-crystal CVD diamond, while the background NV-center population remains largely unaffected.

For me, the broader question is where this type of control can lead. Quantum technologies based on diamond depend not only on discovering useful defects, but also on being able to place, create and modify them in a controlled material environment. A technique that can alter one defect population without substantially disturbing another could eventually become useful as part of that broader toolbox.

The next step is to understand the underlying defect transformations in greater detail and determine how reproducibly they can be controlled. If we can connect laser parameters to specific defect transformations, it may become possible to move from observing selective defect engineering to deliberately designing the defect landscape of diamond for particular applications.

In that sense, the most important result of this work is not simply a new emission line. It is the demonstration that the defects inside diamond do not necessarily have to be treated as an inseparable collection. With the right laser conditions, we may be able to address parts of that defect landscape selectively while leaving quantum-relevant defects such as NV centers intact.

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Lisa Lock

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Robert Egan

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Emmanuel Ediri Umukoro is a graduate student pursuing an M.S. in Physics at North Carolina Central University (NCCU), an HBCU in Durham, North Carolina, and is a Visiting Graduate Student in the Department of Electrical and Computer Engineering at Duke University. His research focuses on quantum defect engineering, laser-based nanofabrication, and advanced spectroscopic characterization of quantum materials, with applications in quantum computing, sensing, and communication. He has published peer-reviewed research in Elsevier and IOP journals, and has presented his work at national quantum research workshops attended by scientists from Google Quantum AI, Yale Quantum Institute, and Princeton University. He is a recipient of competitive travel grants from the NSF Institute for Robust Quantum Simulation and a co-organizer of the IBM Quantum Qiskit Fall Fest 2026. Umukoro holds an Advanced Tier Quantum Excellence Certificate from IBM’s Qiskit Global Summer School.