The race to find materials capable of powering practical quantum technologies has gained a powerful new tool. Researchers at the University of Osaka have developed a first-principles computational framework that can rapidly predict how efficiently atomic defects known as color centers emit light. The method is designed to overcome one of the most persistent obstacles in quantum-materials research: the extraordinary computational cost of determining whether a candidate defect will produce useful single photons or instead lose its energy as heat and lattice vibrations. By replacing many demanding simulations with a small number of strategically selected energy calculations, the framework could allow scientists to screen enormous libraries of semiconductors far faster than previously possible. The findings, published in npj Computational Materials, point toward a new era of high-throughput discovery for quantum emitters used in communication, sensing, and computing.
Color centers are imperfections embedded within otherwise orderly crystal lattices. They can arise when an atom is missing, replaced by another element, or combined with a neighboring defect. Under the right conditions, electrons associated with these atomic-scale structures can transition between discrete energy levels and release individual photons. Unlike the broad, continuous light produced by conventional lamps or many semiconductor devices, a single-photon emitter produces light quanta one at a time. That property makes color centers attractive for quantum communication, where information may be encoded in individual photons, as well as for quantum sensors and processors that rely on precisely controlled electronic or spin states. Yet the presence of an optical transition alone does not guarantee a useful device. A defect must emit efficiently, remain stable, and preserve quantum information rather than surrendering its energy to the surrounding crystal.
The central challenge is the competition between radiative and nonradiative processes. In a radiative transition, an excited electron returns to a lower-energy state by emitting a photon. The corresponding emission rate is commonly represented by ΓZPL, referring to the zero-phonon line, in which the transition occurs without creating or absorbing lattice vibrations. In a nonradiative process, represented by ΓNR, the excitation energy is transferred to phonons—the quantized vibrations of the crystal lattice—instead of becoming light. The fraction of excitations that produce photons is therefore governed by the balance between these channels. A simplified expression for the quantum efficiency can be written as ΓZPL divided by the sum of ΓZPL and ΓNR. Even a defect with a favorable electronic structure can be a poor emitter if phonon-assisted losses dominate.
Calculating that balance from first principles is notoriously demanding. Conventional methods must describe the electronic wave functions of the defect, the motion of many atoms, the coupling between electrons and phonons, and the changes that occur when the defect moves between different charge or spin configurations. In practice, this can require extensive sampling of vibrational coordinates and repeated calculations of potential-energy surfaces. Each additional candidate defect or host material multiplies the computational burden, making exhaustive searches impractical. The result is a bottleneck: researchers may know that thousands of possible color centers exist, but lack an affordable way to determine which ones are bright, stable, and suitable for quantum applications.
The Osaka team addressed this problem by deriving a compact theoretical expression for nonradiative optical losses and pairing it with an effective approximation that captures the most important physics while avoiding a large number of expensive simulations. Instead of mapping every detail of the multidimensional vibrational landscape, the approach extracts the relevant information from a limited set of energy evaluations. These calculations estimate how strongly the electronic transition interacts with structural distortion and how much energy is available to excite phonons. The method then uses those quantities to approximate the nonradiative transition rate. In effect, a complex problem involving countless possible atomic motions is reduced to a manageable calculation of the energetic changes most directly connected to the defect’s optical behavior.
The framework also brings radiative and nonradiative processes into a single, consistent computational picture. Radiative emission depends on factors such as the energy of the optical transition and the strength of the electric-dipole matrix element, which measures how effectively the electronic states couple to light. Nonradiative decay, by contrast, depends on electron–phonon coupling, the displacement of atoms between electronic states, and the availability of vibrational pathways that can absorb the excitation energy. Treating both channels within one first-principles framework allows researchers to estimate not merely whether a color center can emit a photon, but how likely it is to do so before losing its energy to the lattice. According to the researchers, the simplified results showed excellent agreement with conventional calculations, demonstrating that speed need not come at the expense of predictive accuracy.
To test the method against a technologically important system, the team applied it to color centers in silicon carbide. This semiconductor is already a leading platform for quantum research because it combines a wide bandgap, mature fabrication technology, and defects whose electronic and spin properties can be manipulated with light and microwaves. Some silicon-carbide color centers emit in spectral regions relevant to quantum communication, while others possess spin states that can act as qubits. The researchers screened candidate defects for both optical performance and spin suitability. Their calculations identified several promising spin-qubit candidates with sufficiently high spin and correctly recognized emitters that have already been demonstrated experimentally, providing an important validation of the framework.
The potential reach of the method extends well beyond silicon carbide. Because the formulation is not tied to a particular host crystal, it can be applied to defects in a broad range of semiconductors, including materials that have not yet been explored extensively for quantum photonics. It can also evaluate emitters across a wide spectral range, from ultraviolet wavelengths to the telecommunications bands used in optical-fiber networks. That flexibility is crucial because different applications impose different requirements. A quantum repeater may need an emitter whose photons travel efficiently through fiber, while a nanoscale sensor may prioritize stability, brightness, or compatibility with a specific wavelength. A fast screening method could help researchers search for combinations of host materials and defects that would be nearly impossible to investigate one by one using traditional calculations.
The new framework could ultimately transform the way quantum materials are discovered. Rather than beginning with a small number of familiar crystals and testing defects through a slow cycle of theory, fabrication, and measurement, scientists may be able to computationally scan vast candidate spaces before selecting the most promising systems for laboratory development. Such screening could reveal defects with strong optical transitions, weak phonon losses, favorable spin structures, and emission wavelengths tailored to existing photonic infrastructure. The approach may also help explain why some experimentally observed defects perform well while closely related structures fail, providing design principles for engineering brighter and more coherent quantum emitters. By making the hidden competition between photons and phonons computationally accessible, the Osaka researchers have provided a practical route toward faster materials discovery—and potentially toward quantum devices that are more efficient, scalable, and reliable.
Subject of Research: Not applicable
Article Title: Unified first-principles framework for predicting radiative and non-radiative processes in color centers
News Publication Date: 25 August 2026
Web References: https://doi.org/10.1038/s41524-026-02267-8
References: npj Computational Materials, “Unified first-principles framework for predicting radiative and non-radiative processes in color centers,” DOI: 10.1038/s41524-026-02267-8
Image Credits: The University of Osaka
Keywords: Materials science, quantum optics, quantum mechanics, quantum computing, computational physics, photons, phonons, semiconductors, theoretical physics, color centers, quantum emitters, silicon carbide, electron–phonon coupling, quantum materials
