Mems Photonics Chip Shrinks Quantum Computer Control Limits

By many estimates, quantum computers will need millions of qubits to realize their potential applications in cybersecurity, drug development, and other sectors. The problem is that anyone who wanted to control millions of a certain type of qubit simultaneously ran into the problem of trying to control millions of laser beams.

That’s exactly the challenge faced by scientists working on the MITER Quantum Moonshot project, which brought together scientists from MITER, MIT, the University of Colorado at Boulder, and Sandia National Laboratories. The solution they developed came in the form of image projection technology that they believe could also be the solution to many other challenges in augmented reality, biomedical imaging and elsewhere. The device is a one-millimeter square photonic chip capable of projecting the Mona Lisa onto an area smaller than the size of two human eggs.

“When we started, we certainly never imagined that we would create technology that could revolutionize imaging,” says Matt Eichenfield, one of the leaders of the Quantum Moonshot project, a collaborative research effort focused on developing a scalable diamond-based quantum computer, and a professor of quantum engineering at the University of Colorado Boulder. Every second, their chip is capable of projecting 68.6 million individual points of light, called scannable pixels to differentiate them from physical pixels. This is more than fifty times the capability of previous technologies, such as micromirror arrays in microelectromechanical systems (MEMS).

“We have now created a digitizable pixel that is at the absolute limit of what diffraction allows,” says Henry Wen, a visiting scholar at MIT and a photonics engineer at QuEra Computing.

The chip’s distinctive feature is an array of tiny micro-scale cantilevers, which move away from the plane of the chip in response to voltage and act as miniature “ski springboards” for light. Light is channeled along each cantilever via a waveguide and exits at its end. The cantilevers contain a thin layer of aluminum nitride, a piezoelectric that expands or contracts under voltage, thereby moving the micromachine up and down and allowing the array to scan beams of light over a two-dimensional area.

Despite the magnitude of the team’s accomplishments, Eichenfield says the process of engineering the cantilevers went “pretty smoothly.” Each cantilever is composed of a stack of several submicron layers of material and wraps approximately 90 degrees out of plane at rest. To achieve such high curvature, the team took advantage of differences in contraction and expansion of individual layers caused by the physical stresses of the material resulting from the manufacturing process. The materials are first laid flat on the chip. Next, a layer in the chip below the overhang is removed, allowing the stresses in the material to take effect, freeing the overhang from the chip and allowing it to wrap around. The top layer of each cantilever also has a series of silicon dioxide bars perpendicular to the waveguide, which prevent the cantilever from wrapping across its width while enhancing its lengthwise curvature.

A micro-cantilever wiggles and shakes to project light to the right location.Matt Saha, Y. Henry Wen et al.

What was more difficult than engineering the chip itself was understanding the details of creating the images and videos of the chip project. According to Andy Greenspon, a MITER researcher who also worked on the project, developing the process of synchronizing and timing the movement of the cantilevers and light beams to generate the right colors at the right time was a considerable effort. Today, the team has managed to project various videos from a single medium, including clips from the film. A Charlie Brown Christmas.

The chip projected an image of about 125 micrometers of the Mona Lisa.Matt Saha, Y. Henry Wen et al.

Since the chip can project many more points in a given time interval than any previous beam scanner, it could also be used to control many more qubits in quantum computers. The mission of the Quantum Moonshot program is to build a quantum computer that can be scaled up to millions of qubits. So it’s clear that there needs to be a scalable way to control each of them, says Wen. Instead of using one laser per qubit, the team realized that it was not necessary to control every qubit at every moment. The chip’s ability to move light beams over a two-dimensional area would allow them to control all the qubits with far fewer lasers.

Another process Wen thinks the chip could improve is scanning objects for 3D printing. Today, this typically involves using a single laser to scan the entire surface of an object. The new chip could, however, use thousands of laser beams. “I think now you can take a process that would have taken hours and maybe reduce it to minutes,” says Wen.

Wen is also excited to explore the potential of different cantilever shapes. By changing the orientation of the bars perpendicular to the waveguide, the team was able to make the cantilevers bend into helices. Wen says such unusual shapes could be useful for creating a lab-on-a-chip for cell biology or drug development. “A lot of this stuff is imaging, scanning a laser on something, either to image it or to stimulate a response. And so we could make one of these ski jumps not just curve upwards, but actually curl around and then move around and scan a sample,” Wen says. “If you can think of a structure that would be useful to you, we should try it.” »