Tiny new device could enable giant future quantum computers

Researchers have made a major advance in quantum computing with a new device that is nearly 100 times smaller than the diameter of a human hair.
Published in the journal Nature Communications, the breakthrough optical phase modulators could help unlock much larger quantum computers by enabling efficient control of lasers required to operate thousands or even millions of qubits—the basic units of quantum information.

Critically, the team of scientists have developed these devices using scalable manufacturing, avoiding complex, custom builds in favor of those used to make the same technology behind processors already found in computers, phones, vehicles, home appliances—virtually everything powered by electricity (even toasters). 

Led by Jake Freedman, an incoming PhD student in the Department of Electrical, Computer and Energy Engineering; Matt Eichenfield, professor and the Karl Gustafson Endowed Chair in Quantum Engineering; and collaborators from Sandia National Laboratories, including co-senior author Nils Otterstrom, they created a device that is not only tiny and powerful, but also practical and inexpensive to mass-produce. 

Their device uses microwave-frequency vibrations, oscillating billions of times per second, to manipulate laser light with extraordinary precision.

These ultra-fast vibrations give researchers direct control over the phase of a laser beam, allowing the chip to generate new laser frequencies with high stability and efficiency, all essential for building quantum computing, quantum sensing and quantum networking technologies.

Why quantum computers depend on precise optical frequency control

Among the leading approaches to quantum computing are trapped-ion and trapped-neutral-atom systems, which store information in individual atoms. 
To operate these qubits, researchers “talk” to each atom using precise laser beams, allowing them to give the instructions to do computations.
Each laser’s frequency must be tuned with extreme accuracy, often to within billionths of a percent or even smaller.

“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,” Freedman said. “But to do that at scale, you need technology that can efficiently generate those new frequencies.”

Today, those frequency shifts are made using bulky table-top devices that consume significant amounts of microwave power. 

Current setups work well for small lab experiments and quantum computers with small numbers of qubits, but they cannot scale to the tens or hundreds of thousands of optical channels required for future quantum computers.

“You’re not going to build a quantum computer with 100,000 bulk electro-optic modulators sitting in a warehouse full of optical tables,” 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 100 times less heat, you’re much more likely to make it work.”

The device can generate new frequencies of light through efficient phase modulation that consumes roughly 80 times less microwave power than many commercial modulators. 

Using less power reduces heat and allows many more channels to be placed close together—even on a single chip.

Together, these features turn the chip into a powerful, scalable system for managing the complex dance that atoms must perform  to make quantum computations.

Built using the world’s most scalable manufacturing technology

One of the most significant aspects of the project is that it was produced entirely in a “fab” or foundry, the same type of facility used to make advanced microelectronics.

“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.”

According to Otterstorm, they’ve taken modulator devices which were previously expensive and power hungry and made them more efficient and less bulky. 

“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,” Otterstorm said. 

The team is now developing fully integrated photonic circuits that combine frequency generation, filtering, and pulse-carving on the same chip, bringing the goal of a complete operational chip closer to reality.

Moving forward, they will collaborate with quantum computing companies to test versions of these chips inside state-of-the-art trapped-atom and trapped-neutral-atom 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.” 

This project was supported by the U.S. Department of Energy through the Quantum Systems Accelerator program, a National Quantum Initiative Science Research Center.

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