Optical phase modulators with scalable platforms are essential for large-scale quantum computing. Quantum computers will require thousands, even millions, of channels to independently control each qubit, and, to support this requirement, optical phase modulators will need to be mass-producible as well as powerful. In response to this need, researchers at the University of Colorado-Boulder, in collaboration with Sandia National Laboratories, developed an on-chip optical phase modulator that enables high optical power handling while maintaining efficient modulation. They manufactured the modulator using CMOS, the standard technology used in the manufacture of microelectronics. Optical chip developed in the study with laser light from an optical fiber array. Courtesy of Jake Freedman. The visible-light, gigahertz-frequency, acousto-optic phase modulator combines a piezoelectric transducer and a photonic waveguide within a single, wavelength-scale structure that confines a propagating optical mode and an electrically excitable breathing-mode mechanical resonance. The on-chip modulator uses microwave-frequency vibrations, oscillating billions of times per second, to manipulate laser light with extraordinary precision and provide direct control of the beam’s phase. By tuning the device’s geometry to optimize optomechanical interaction, the researchers achieved modulation depths up to 4.85 radian (rad) with 80 mW of applied microwave power at 2.31 GHz in a 2-mm-sized device. The team obtained resonant modulation with only about 1.3 volts of power — the lowest voltage reported for an acousto-optic phase modulator — using 15× less voltage and 100× less microwave power compared to current modulators for quantum control. The modulator is designed to support trapped-ion and trapped-neutral-atom quantum computing systems. Atom- and ion-based quantum computers store information in individual atoms and use laser beams to communicate instructions to each atom. The frequency of each laser must be tuned with extreme accuracy — often to within billionths of a percent. “Creating new copies of a laser with very exact differences in frequency is one of the most important tools for working with atom- and ion-based quantum computers,” researcher Jake Freedman said. “But to do that at scale, you need technology that can efficiently generate those new frequencies.” Currently, these frequency shifts are made using bulky table-top devices that consume a lot of microwave power. While such a setup can work for small lab experiments and quantum computers with small numbers of qubits, it cannot scale to the tens or hundreds of thousands of optical channels that will be required for future quantum computers. 3D rendering of the device including the optical waveguide, piezoelectric actuator, and metal routing layers essential for quantum computing. Courtesy of Jake Freedman. “You’re not going to build a quantum computer with 100,000 bulk electro-optic modulators sitting in a warehouse full of optical tables,” professor Matt Eichenfield said. “You need some much more scalable ways to manufacture them, that don’t have to be hand-assembled and with long optical paths. While you’re at it, if you can make them all fit on a few small microchips and produce 100x less heat, you’re much more likely to make it work.” The on-chip acousto-optic phase modulator consumes about 80× less microwave power than many commercial modulators do to generate new frequencies. This reduces heat and allows more channels to be placed close together, even on a single chip. To ensure scalability, the researchers manufactured the modulator on a 200-mm wafer in a volume CMOS foundry. “CMOS fabrication is the most scalable technology humans have ever invented,” Eichenfield said. “Every microelectronic chip in every cell phone or computer has billions of essentially identical transistors on it. So, by using CMOS fabrication, in the future, we can produce thousands, or even millions, of identical versions of our photonic devices, which is exactly what quantum computing will need.” The next-generation optical phase modulator is designed to be more energy-efficient, cheaper, and more streamlined than existing devices. “We’re helping to push optics into its own ‘transistor revolution,’ moving away from the optical equivalent of vacuum tubes and towards scalable, integrated photonic technologies,” researcher Nils Otterstrom said. The team is now working on the development of fully integrated photonic circuits that combine frequency generation, filtering, and pulse-carving on the same chip. This work will bring the goal of a completely operational chip closer to reality. In the future, the researchers plan to collaborate with quantum computing companies to test versions of the chip inside state-of-the-art atom- and ion-based quantum computers. “This device is one of the final pieces of the puzzle,” Freedman said. “We’re getting close to a truly scalable photonic platform capable of controlling very large numbers of qubits.” The research was published in Nature Communications (www.doi.org/10.1038/s41467-025-65937-z).