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Small Invention, Massive Quantum Impact
A tiny invention helping make massive strides in quantum computing.
Written by Alexandra Frost
IT’S A HUNDRED TIMES SMALLER than a single strand of hair. And it could lead to significant progress in the future of quantum computing, generating new frequencies of light through efficient phase modulation. It’s the product of a decade of work on the piezo-optomechanical devices, which means they use piezoelectric actuators in the microchips to deform and strain photonic structures.
Now, the research conducted by Matt Eichenfield, a distinguished faculty member and joint appointee at Sandia National Labs, and photonics & quantum engineering professor at the University of Colorado Boulder and his team has been published in Nature Communications in October 2025, in a paper called “Gigahertz-frequency acousto-optic phase modulation of visible light in a CMOS-fabricated photonic circuit.”
The exciting part? Researchers concluded that, to their knowledge, it’s the lowest voltage in similar products to date, consuming roughly 80 times less microwave power than many commercial modulators. Because it consumes less power, reducing heat, you can place more channels together on a single tiny chip, all without negatively affecting each other.
Eichenfield, along with incoming doctoral student Jake Freedman, created the “practical and inexpensive to mass produce” device.
An optical chip developed with laser light from an optical fiber array. Photo: Jake Freedman/ University of Colorado Boulder
The Mission
“We needed to go beyond just creating those pulses and actually be able to create new frequencies of light on the chip in all those quantum computers, so you don’t just have a single frequency or color of light that you need to address the atoms with,” Eichenfield said. “It turns out that often what you need to do is have two very, very precisely spaced colors of light—two frequencies of light that have to interrogate the atom or ion at the same time. And the only way to make that so that those two colors or frequencies stay stable with respect to each other, is to produce the second one from the first one.”
Size and scale were key considerations. “The reason you want to reproduce this function on a chip is you can fit many more channels, much smaller space, with higher performance than these bulky crystals, which are big, expensive, and consume a lot of power. Even just the materials are difficult to source. They’re big,” he said. “So it’s fine if you’re doing hundreds of qubits, but quantum computers need to scale to having tens of thousands, hundreds of thousands, millions of qubits—and there’s just no real, feasible way to take those bulky technologies and make enough of them at a low enough cost, with low enough power, and all that stuff to do it without some sort of a chip scale technology.”
He explained that when you apply the voltage, the whole structure guiding the light gets wider and narrower periodically. “This literally changes the speed of light through the system periodically too,” he said.
The Challenge
Eichenfield encountered several obstacles along the way, the largest being generating the original idea. “One challenge was just coming up with a novel way to do this—nobody has ever made this kind of an integrated phase modulator before,” he said.
The second challenge was trying to make it have higher performance than even the commercial state-of-the-art products, Eichenfield added. He shared that the best products you can buy are “enormous”—the size of a deck of cards and less powerful. “Actually, if you want to really crank up the amplitude of the tones, the new laser tones you're making, it can't make as much power in those laser tones as ours,” Eichenfield said. So, he wanted to do better. And succeeded.
Finally, the fabrication process is quite complicated. “We fabricated in Sandia National Labs, CMOs foundry, so they make micro electronic circuits for national security purposes,” he said. “We had to modify the processes that they use in order to be able to adapt that foundry’s capabilities to make what we wanted to make. And we worked really hard with the people at Sandia to get that done. And then after they were made, [the challenge] was actually just characterizing them.”
That stage took quite a while, he said, as they had to build a complicated experimental setup to measure each of the new tones to ensure they were generated precisely. Eichenfield asked, “We had to figure out not just whether we could do it, but can we do it reliably? If we make millions of these, how many of them will work?”
Top-down image of the on-chip phase-modulator devices taken with a microscope. Photo: Andrew Leenheer/University of Colorado Boulder
The device’s continuous translational symmetry is broken by periodically placed nanopillar supports along its length. Photo: Jake Freedman/University of Colorado Boulder
High-Stakes Decisions
These specific materials—Complementary Metal on Silicon (CMOS)—were the motivation to work with the foundry. “If we can constrain ourselves to use these special materials that are only compatible with that technology and the processes that they use, then once we get it to work, it will immediately be scalable at the scale that is necessary to make quantum computers actually work,” Eichenfield said.
The downside was the “very strict limitations on the materials, and there are no materials in that set of materials that you can use in a CMOS foundry that guide the right color of light and that are electro-optic,” he said. “So you can’t just apply electric fields and change the speed of light directly.”
With long turnaround times for experiments, such as four to six months, errors can be costly. “There are about 200 steps that the fabrication facility does to make this wafer. And it’s very time-consuming. It’s also expensive. It costs $100,000 or $200,000 to kind of make one of these sets of wafers,” Eichenfield explained.
“People believe in the technology, so the pressure is just in not making mistakes, which then slows it down more than it needs to be. It already takes a long time, so you don’t want to screw something up and then have to wait another six months to try again,” he added.
Eichenfield plans to continue this work indefinitely, supported by funding through the Quantum Systems Accelerator Center, which was recently renewed.
“It will also fund this next stage of work where we make more sophisticated devices targeted at specific ions or atoms for real quantum computing applications,” he said.
Alexandra Frost is an independent writer and content strategist in Cincinnati.
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