Micro-Cantilever Photonic Chip Scales Quantum Computing and High-Resolution Imaging

Researchers involved in the MITRE Quantum Moonshot project have developed a one-square-millimeter photonic chip capable of projecting 68.6 million individual spots of light per second. This technology, which utilizes nanoscale waveguides integrated on piezoelectric cantilevers, provides a scalable method for controlling large arrays of qubits in quantum computers and offers new possibilities for high-speed 3D printing and biomedical imaging.

The project is a collaborative effort between scientists from MITRE, MIT, the University of Colorado at Boulder, and Sandia National Laboratories. While the primary goal was to address a hardware bottleneck in quantum computing, the resulting device can project high-resolution images and video onto surfaces smaller than two human egg cells. In one demonstration, the chip projected an image of the Mona Lisa at a scale of approximately 125 micrometers.

Solving the Quantum Laser Beam Problem

To reach their full potential in cybersecurity and drug development, quantum computers may eventually require millions of qubits. However, controlling such a vast number of qubits traditionally requires an equal number of laser beams, a requirement that is logistically impossible to meet.

The new photonic chip addresses this challenge by projecting data into free space. Because not every qubit needs to be controlled at every single moment, the chip’s ability to move light beams across a two-dimensional area allows researchers to control a vast array of qubits using significantly fewer lasers.

The Engineering of Ski-Jump Cantilevers

The device’s functionality relies on an array of micro-scale cantilevers that act as miniature ski-jumps for light. Light is channeled through a waveguide along the length of each cantilever and exits at the tip. These structures are fabricated in a volume complementary metal–oxide–semiconductor (CMOS) foundry.

Each cantilever consists of a stack of several submicrometer layers of material. To create the necessary curvature, the team used differences in the contraction and expansion of individual layers caused by physical stresses during the fabrication process. Once a layer below the cantilever is removed, the material stresses cause the cantilever to curl approximately 90 degrees out of the plane at rest.

To maintain structural integrity and precision, the top layer of each cantilever features silicon dioxide bars running perpendicular to the waveguide. These bars prevent the cantilever from curling along its width while improving its length-wise curvature.

The movement of the cantilevers is driven by a thin layer of aluminum nitride, a piezoelectric material that expands or contracts under voltage. This allows the micromachine to move up and down, enabling the array to scan beams of light over a two-dimensional area at CMOS-level voltages.

Performance and Technical Benchmarks

The researchers refer to the projected spots of light as scannable pixels to distinguish them from physical pixels. The chip achieves a footprint-adjusted spot rate of 68.6 mega spots s–1 mm–², which is more than 50 times the capability of existing micro-electromechanical systems (MEMS) micromirror arrays.

We have now made a scannable pixel that is at the absolute limit of what diffraction allows.

Henry Wen, visiting researcher at MIT and photonics engineer at QuEra Computing

The device exhibits kilohertz-rate mechanical resonances with quality factors exceeding 10,000. Beyond static images, the team has successfully synchronized the motion of the cantilevers and light beams to project full-color video, including clips from the movie A Charlie Brown Christmas.

Applications Beyond Quantum Computing

The high-speed scanning capabilities of the chip have immediate implications for other industries. In 3D printing, current scanning often relies on a single laser to cover an entire object surface, a process that can take hours. By employing thousands of laser beams via the photonic chip, the time required for such processes could be reduced to minutes.

The technology also shows promise for biomedical imaging and drug development. Henry Wen noted that by changing the orientation of the perpendicular bars, the cantilevers can be made to curl into helixes.

These helical shapes could be used in lab-on-a-chip devices for cell biology, where a laser could curl back around to scan over a sample and stimulate a specific response.