Chemists Recast Diamond Qubits as Molecules, Accelerating the Search for Quantum Materials

Quantum technology has long promised sensors more sensitive than anything currently available and computers capable of solving highly complex problems far faster than any traditional supercomputer on Earth today. Yet the bottleneck has often been not physics but chemistry: finding the right materials to host quantum information has been a slow, computationally punishing process. Now a researcher at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) has developed a faster way of identifying the best diamond-based materials for quantum computers, an approach that has already flagged promising candidates for practical quantum sensors and computers that could one day transform scientific research as a whole. The research, published in the journal ACS Central Science, has already drawn attention from other experts in the field, suggesting that a methodological shift may be underway in how the quantum community hunts for its building blocks.

The central insight of the new work is deceptively simple. Many types of materials are currently being considered for use in quantum technology, but most can only hold a stable quantum state when chilled to extreme temperatures. Diamond-based materials offer a compelling alternative because they remain functional at room temperature, removing one of the most burdensome engineering requirements in the field. Pure diamond, however, which is made entirely of carbon atoms, will not work on its own. Defects in the diamond are essential for storing and processing information. A defect might mean a carbon atom is missing from its usual spot, a different kind of atom has taken its place, or both. The clusters of atoms closest to a defect form the fundamental information processing unit of a quantum computer or sensor, known as a qubit.

Simulating those qubits has traditionally been a computational nightmare. Because a defect sits inside an extended crystal lattice, faithful simulations have required modeling enormous numbers of atoms, pushing even powerful computers to their limits and making the systematic screening of candidate defects impractical. Mark Martirez, a staff research scientist at PPPL, has solved this problem by carving out a small cluster of just 16 to 30 atoms around the defect. By treating this cluster as an isolated molecule, he can apply highly accurate quantum chemical tools that chemists have been using for decades to study simple compounds, importing a mature computational arsenal into a domain that has traditionally been approached as a problem in solid-state physics.

The payoff is dramatic. Because the qubits are treated as molecules, the cost of calculating these defects becomes equivalent to the cost of modeling a simple molecule, according to Martirez, who described the method as one that really opened the floodgates in terms of how qubits can be assessed. Using the new approach, the researchers were able to simulate how qubits would respond to light and microwave pulses far faster than ever before. That acceleration matters because reading information out of a qubit is a dynamic process: scientists shine laser light on qubits and pulse microwaves at them to read back the information stored within, and predicting those responses accurately is essential to knowing whether a candidate defect will ever be useful in a real device.

The simulations led the team to discover new boron and oxygen-based defects that could make useful qubits, expanding the palette of options beyond the defect that has dominated the field. Most quantum diamond research has focused on the nitrogen-vacancy defect, in which one carbon atom is replaced by a nitrogen atom and a nearby spot, normally holding another carbon atom, is left empty. When scientists shine a laser on this particular kind of qubit, it emits a red light if it is in a particular quantum state. The oxygen-based defects Martirez is studying shine blue, while the boron-based defects emit ultraviolet light. These different color centers could potentially be used in different ways within a single quantum device, opening architectural possibilities that a single defect type cannot provide.

The practical significance of multiple colors is easier to grasp with a concrete picture. One could imagine combining different qubits with different optical responses, so that a researcher can probe one qubit without disturbing the other, Martirez explained. In a multi-qubit device, that selectivity could simplify control and readout, two of the most delicate operations in quantum engineering. Rather than relying on spatial addressing alone, engineers could in principle use wavelength to distinguish qubits, addressing the blue-emitting centers and the ultraviolet-emitting centers independently. Such flexibility could prove valuable as researchers move from isolated qubits toward the densely integrated systems that practical quantum computers and sensors will demand.

Beyond the immediate candidates, fully understanding the chemistry of qubits could transform the very concept of what a qubit structure should be. Scientists have often treated diamond-based qubits as a physics problem, focusing on the quantum mechanical behavior of spin states within a crystal. The new research shows that they can also be understood through chemistry, enabling scientists to design and build qubits the way a chemist designs custom molecules, such as a new medication, for a specific purpose. In that framing, a defect in diamond is not an imperfection to be tolerated but a synthetic target to be engineered, with its atomic composition and local geometry chosen deliberately to produce the desired optical and quantum properties.

Martirez also sees a longer and somewhat recursive horizon for his field. When he thinks about the future, he finds it interesting to note that quantum chemistry may help develop tools to enrich itself in the decades to come. A practical multi-qubit system would vastly improve the level of accuracy of quantum chemistry calculations, he said. With such systems in hand, researchers could describe larger molecules, biomolecules, proteins and everything like that in a more accurate way, and that could improve all the chemical-adjacent industries, such as pharmaceutical science and materials science. Even the fundamental understanding of molecular systems could be enriched, closing a loop in which chemistry builds the quantum devices that in turn sharpen chemistry’s own predictive power.

There is also a disciplinary message in the work. Martirez encouraged other chemists to consider research in solid-state physics, arguing that at this moment in time there is a great emphasis on building the first state-of-the-art qubit computer, but that it is not just physicists who should be participating in this research. Chemists, he noted, have decades of developed intuition about chemical systems that could be easily translated into understanding defects in solids as well. The new method is, in effect, an invitation: by lowering the computational barrier to entry, it allows that chemical intuition, honed on small molecules, to be applied directly to the atomic clusters that function as qubits inside a crystal.

The research was funded by PPPL’s Laboratory Directed Research and Development program under prime contract number DE-AC02-09CH11466, with additional support from the DOE Office of Science, Office of Fusion Energy Sciences. The work reflects the laboratory’s broader mission of using plasma, the fourth state of matter, to address difficult science and technology challenges, including fusion energy, nanoscale fabrication, quantum materials and devices, and sustainability science, with Princeton University managing the laboratory for the Department of Energy’s Office of Science. For a field that has often measured progress in cryogenic kelvins and brute-force computation, the idea that a cluster of a few dozen atoms, treated as a molecule, could unlock faster and more accurate predictions of qubit behavior is a striking reframing. If diamond color centers in red, blue and ultraviolet can be designed like custom molecules, the search for room-temperature quantum devices may become less an expedition into exotic physics and more a discipline of molecular design, with chemists and physicists working side by side on the technology of the future.

Subject of Research: Computational quantum chemistry of diamond color-center defects for solid-state qubits

Article Title: Creating the technology of the future: Quantum chemistry unlocks new possibilities

Article References: Creating the technology of the future: Quantum chemistry unlocks new possibilities. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: quantum computing, qubits, diamond defects, quantum chemistry, color centers, nitrogen-vacancy, room-temperature quantum, quantum sensors, PPPL, solid-state physics, molecular simulation, ACS Central Science