We're trying to make a crystal that doesn't want to exist
At Princeton's Plasma Physics Laboratory, scientists are cultivating imperfect diamonds — stones grown not for beauty but for their deliberate atomic flaws — as the material foundation of a new generation of quantum sensors. These nitrogen-vacancy defects, tiny absences in a carbon lattice, become the sensing instruments through which magnetic fields, temperatures, and electric currents reveal themselves with extraordinary precision. It is a reminder that in science, as in life, the most profound capabilities often emerge not from perfection but from carefully chosen imperfection. The work positions humanity at the threshold of sensing what was previously hidden — beneath the earth, within the body, inside the circuit.
- Growing diamonds with controlled atomic defects is a materials science tightrope — push the chemistry too far and the crystal collapses into graphite, erasing the work entirely.
- The central tension is a paradox: packing more quantum bits into a diamond increases sensing power but also amplifies the noise that destroys the very quantum properties being harnessed.
- Researchers are attempting to resolve this by co-doping diamonds with phosphorus, freeing nitrogen-vacancy centers from doing double duty and allowing denser, cleaner qubit arrangements.
- A tight, continuous feedback loop between PPPL and Princeton University — unusual in the field — is accelerating the pace of discovery by coupling growth experiments directly to measurement and analysis.
- The immediate target is an atomically flat diamond surface, a seemingly modest goal that would unlock the ability to place individual atoms at chosen locations and transform quantum sensing from promising to practical within a year.
At Princeton Plasma Physics Laboratory, researchers are growing diamonds no jeweler would prize — stones deliberately seeded with atomic-scale flaws that make them extraordinarily useful. These imperfections, called nitrogen-vacancy centers, transform lab-grown diamonds into quantum sensors capable of detecting submarine magnetic signatures, guiding navigation without GPS, and mapping what lies hidden underground.
The difficulty lies in the chemistry itself. Diamond and graphite are both pure carbon, differing only in how their atoms are arranged. Keeping carbon locked in diamond's rigid lattice while introducing precise defects — without the whole structure reverting to graphite — is, as lab director Alastair Stacey describes it, making chemistry that doesn't want to happen. Each nitrogen-vacancy center creates a qubit: a quantum bit that responds to magnetic fields, temperature shifts, and electric currents, glowing visibly when probed with laser light.
The deeper challenge is scaling up. More qubits mean more sensing power, but the nitrogen creating those qubits also introduces noise that corrupts quantum performance. The laboratory's solution is co-doping — adding phosphorus to take over the electron-supply role, leaving nitrogen-vacancy centers to function cleanly and allowing qubits to be packed more densely. The team is also partnering with Element Six, a synthetic diamond industry leader, to access industrial-scale reactors for experimentation.
What distinguishes PPPL's approach is its unusually close collaboration with Princeton University, where growth experiments and measurement analysis inform each other in real time rather than across conference tables. The near-term milestone — achieving an atomically flat diamond surface — would allow individual atoms to be placed at precise, chosen locations rather than settling at random. Within a year, Stacey believes, that platform could open the door to sensors capable of detecting magnetic fields in human cells or electric fields at the nanometer scale: capabilities that do not yet exist, measuring what currently remains hidden.
At the Princeton Plasma Physics Laboratory, researchers are growing diamonds that nobody would want on an engagement ring. These lab-made stones are studded with atomic-scale flaws—deliberate imperfections that turn them into something far more valuable than sparkle. They are becoming the foundation of quantum sensors so sensitive they could detect the magnetic signature of a submarine, guide a plane when GPS fails, or map what lies buried beneath the earth.
The challenge sounds simple until you try it: grow a diamond with the right defects in the right places, without watching it transform into graphite right before your eyes. Alastair Stacey, who leads the Quantum Diamond Laboratory at PPPL, describes the work as trying to make "a crystal that doesn't want to exist and chemistry that doesn't want to happen." Diamond and graphite are both made of carbon, but their atoms are arranged in fundamentally different ways. In graphite, the atoms stack in flat sheets that slide past each other—the stuff of pencil cores. In diamond, they lock into a rigid three-dimensional lattice, which is why the material is hard and transparent. Same element, radically different properties, all because of atomic arrangement. The trick is keeping the atoms locked in place while introducing the specific flaws that make the material useful.
Those flaws are nitrogen-vacancy centers, or NV centers. A nitrogen atom replaces a carbon atom in the diamond lattice, leaving an empty spot beside it. That empty spot, that absence, becomes the quantum bit—the qubit—that researchers can manipulate with laser light and microwave pulses. The diamond glows in response, and scientists read that glow to understand what the qubit has sensed. A passing magnetic field, a temperature shift, an electric current—all of these nudge the qubit in measurable ways. The concept is simple enough that you can demonstrate it with an office laser pointer, a bar magnet, and a pink diamond. Point the laser at the stone and it glows. Bring the magnet closer and the glow dims. But real quantum sensing requires far more precision and control than a parlor trick allows.
The more qubits packed into a diamond, the more powerful the sensor becomes. But here is where the problem emerges: every NV center needs an extra electron to function, and right now that electron comes from the surrounding nitrogen in the crystal—the same nitrogen creating the NV centers in the first place. It is convenient but messy. The nitrogen introduces noise that corrupts the quantum properties researchers are trying to protect. Pack more qubits into the crystal and the noise gets worse. The laboratory's answer is co-doping: adding a second element, phosphorus, to the mix. Now the NV centers remain, but nitrogen is no longer doing double duty. The goal is a crystal where qubits can be packed more densely without sacrificing their quantum properties, and eventually placed at precise locations rather than scattered at random.
PPPL is not working alone. The laboratory has partnered with Element Six, a world leader in synthetic diamond production since 1946, which is providing industrial diamond reactors for experimentation. The work also depends on a tight collaboration between PPPL and Princeton University that is unusual in the field. Most diamond-quantum research groups ship samples back and forth and compare notes at conferences. Here, the teams routinely swap ideas and consider new approaches together. Nathalie de Leon, an associate professor of electrical and computer engineering at Princeton and co-director of the university's Quantum Institute, originally proposed the idea of the Quantum Diamond Laboratory because she understood that national labs have capabilities no one else possesses. The arrangement allows Princeton to make use of PPPL's infrastructure while PPPL benefits from the university's measurement and analysis expertise. The feedback loop is constant and deliberate: growth experiments are conceived in the context of specific scientific questions, not random attempts. When the growth side changes something, the measurement side observes the result, and both teams adjust their approach together.
The near-term goal sounds almost mundane: making the diamond surface flat at the atomic scale. Imagine a countertop with absolutely no scratches or grooves, right down to the last atom. Right now, when the team exposes a diamond surface to plasma, atoms land and lock into place somewhat randomly. A truly flat surface would provide a stable, predictable foundation. It would allow researchers to place individual atoms at specific, chosen locations in the crystal rather than letting them settle wherever they land. Silicon has already achieved this level of control. For diamond, it remains the frontier. Within the next year, Stacey said, the team is focusing on achieving that flat surface to create a platform for exploration. Once they have it, the implications ripple outward: extremely reliable yet sensitive sensors that can detect tiny magnetic fields in electronic circuits or human cells, devices that can measure electric fields, temperature, and strain down to the nanometer scale. That kind of sensing capability does not exist today. For researchers gathering essential data with these tools, it would mean the difference between what is possible and what remains hidden.
Notable Quotes
We're trying to make a crystal that doesn't want to exist and chemistry that doesn't want to happen. If you do this wrong, the diamond turns to graphite right in front of your eyes.— Alastair Stacey, Quantum Diamond Laboratory director
Usually, what we're trying to do is change something on the growth side that then allows us to see something on the measurement side, and then we have to have a very tight feedback loop between both parts of it.— Nathalie de Leon, Princeton University and PPPL
The Hearth Conversation Another angle on the story
Why does it matter that these diamonds have flaws? Wouldn't a perfect diamond be better?
The flaws are the whole point. A perfect diamond is just a hard, transparent rock. But a nitrogen-vacancy defect—that empty spot next to a nitrogen atom—becomes a quantum bit. It's like the difference between a piece of glass and a piece of glass with a tiny antenna built into it.
So you're deliberately making the diamond imperfect?
Exactly. We're engineering the imperfection. We want nitrogen atoms in specific places, creating those empty spots. Without them, there's no quantum sensor at all.
You mentioned the risk of it turning into graphite. How close are you to that edge?
Very close. The chemistry wants to make graphite. We're fighting against the natural tendency of carbon atoms to arrange themselves in flat sheets. One wrong move—wrong temperature, wrong plasma composition, wrong timing—and you lose the whole crystal. It's why Stacey says we're trying to make something that doesn't want to exist.
What's the strategic importance here? Why does the U.S. care about this?
Whoever masters diamond-based quantum sensors first gets a significant edge. These sensors can detect submarine signatures, guide aircraft when GPS is jammed, map what's underground. The technology is real. The bottleneck is the material. Right now, we can't grow it reliably enough.
And the co-doping approach—adding phosphorus—that solves the noise problem?
It removes nitrogen from doing two jobs at once. Before, nitrogen was both creating the qubits and supplying the electrons they need, which created interference. Now phosphorus supplies the electrons, and nitrogen just creates the qubits. Cleaner signal, denser packing, more powerful sensors.
What happens in the next year?
We're chasing an atomically flat surface. Once we have that, we can start placing qubits exactly where we want them instead of wherever they happen to land. That's the frontier. Silicon got there years ago. Diamond is still trying.