Diamond optomechanical crystals for high-frequency strain and comb generation

Light and motion are usually thought of as separate worlds. Light zips through space at incredible speeds, while motion is the slow, heavy shifting of solid things. Yet in a growing field of physics, scientists are learning to make these two worlds talk to each other. They build tiny machines where light bounces back and forth, pushing and pulling on the material itself. When the light is strong enough and the machine is small enough, the photons—the particles of light—can cool the machine down to its quietest possible state, or they can make it vibrate with such precision that it becomes a tool for sensing the universe. This interaction, where light controls motion and motion changes light, is the foundation for a new generation of technology that could one day link the microwave signals used in our phones with the light signals that carry data across the internet.

For this to work, the materials used must be exceptional. They need to be stiff enough to vibrate very fast, clear enough to let intense light pass through without heating up, and capable of holding onto quantum information. Diamond is a perfect candidate. It is the hardest natural material, which means it can vibrate at incredibly high speeds. It is also an excellent conductor of heat, so it does not melt under the power of a laser, and it can host tiny defects that act as quantum bits, the basic units of future quantum computers. Researchers have long wanted to build devices that use diamond to harness this interaction, but making a diamond structure small enough to control both light and sound simultaneously has been a difficult challenge.

A team of researchers has now built a working version of such a device. They created a tiny beam of single-crystal diamond, suspended in the air and patterned with a precise array of holes. This structure acts like a trap for both light and sound. The holes are arranged to create a mirror that reflects light and sound waves back into the center of the beam, keeping them confined in a very small space. The researchers designed this beam to be incredibly narrow, only a few hundred nanometers wide, which forces the light and the sound waves to interact strongly. When they shine a laser into this diamond beam, the light does not just pass through; it pushes on the diamond, causing it to vibrate. Because the diamond is so stiff, these vibrations happen at a frequency of about 12 billion cycles per second, a speed far too fast for the human ear to hear but perfect for high-speed technology.

The team found that they could make this diamond beam vibrate on its own, without any external shaking. By tuning the laser to a specific frequency, they pushed the system past a tipping point where the light started to feed energy into the motion faster than the diamond could lose it. This caused the beam to enter a state of self-sustained oscillation, vibrating continuously with a large amplitude. As the diamond vibrated, it modulated the light passing through it, creating a series of new light frequencies, or colors, spaced evenly apart. This collection of colors is known as a frequency comb. In this experiment, the researchers generated a comb that spanned a range of 143 billion cycles per second, with the individual colors spaced 12 billion cycles per second apart. This is a much wider range and a larger spacing than what has been achieved in similar devices made from other materials, demonstrating the unique power of the diamond platform.

By analyzing the shape and intensity of this light comb, the researchers were able to measure exactly how much the diamond was moving. They calculated that the surface of the diamond was moving back and forth by a distance of 130 picometers. To put this in perspective, this is roughly the width of a single atom, but the motion is happening at a speed of 12 billion times per second. This movement creates a massive amount of strain, or stretching and squeezing, within the crystal lattice of the diamond. The total strain reached a level of 0.0011, which is more than fifty times stronger than what has been achieved in previous diamond experiments. This level of strain is significant because it is strong enough to potentially control the quantum states of defects inside the diamond.

The implications of this work extend beyond just creating a new type of light source. The ability to generate such strong strain at such high frequencies opens a direct path to controlling the quantum bits found in diamond. These quantum bits, which are defects in the diamond crystal, can be manipulated by the mechanical strain of the vibrating beam. The researchers showed that their device could produce strain levels sufficient to influence these quantum states, suggesting a way to link the mechanical motion of the diamond to its internal quantum properties. This could lead to new ways of storing information or converting signals between different forms of energy. The device operates at room temperature, which is a major advantage, as it does not require the extreme cold usually necessary for quantum experiments. The researchers confirmed their findings through detailed measurements of the light and sound interactions, verifying that the theoretical models of how light and motion couple in diamond were correct.

This achievement represents a significant step forward in the field of optomechanics. By proving that a diamond crystal can support high-frequency vibrations and strong light-matter interactions at room temperature, the team has provided a robust platform for future experiments. The device is capable of generating complex patterns of light and exerting precise mechanical forces, all within a structure smaller than a human hair. The success of this experiment suggests that diamond-based systems could become a standard tool for building quantum technologies, offering a way to bridge the gap between the mechanical world and the quantum world. The researchers plan to take the next step by integrating specific quantum defects into these vibrating beams, aiming to demonstrate direct control over quantum states using mechanical motion. This work lays the groundwork for a future where light, motion, and quantum information are seamlessly integrated into a single, powerful technology.