Tiny tunes: Scientists create diamond radio receiver on atomic level

Researchers at Harvard University have created the world's smallest radio receiver – and it's made from diamonds. The radio is based on nano-sized flaws in the pink diamond, with functional building blocks the size of only two atoms. 

While the sound quality of the receiver may not receive any awards, the world's smallest radio receiver works perfectly for playing music on a local radio station. It's a device built on a micro-scale unheard of when human-created radio transmissions were first invented in the late 19th century.

In addition to its Lilliputian dimensions, the pink diamond basis of the receiver means that this piece of nanotechnology is highly resistant to external conditions, making future versions of the device ideal for use in space or other extreme environments. The technology at the core of the receiver might also be used in quantum computing, potentially pushing future computer processing power forward by leaps and bounds.

A normal radio has five components, including its receiver: a power source, a transducer (which converts the high-frequency electromagnetic signal in the air to a low-frequency electric current), some sort of speaker to translate that current into sound, and a tuner to isolate and amplify the specific EM wave the listener wishes to access. According to a Harvard statement, the receiver in this device is based on imperfections in the pink diamonds called nitrogen-vacancy (NV) centers. These NV centers are tiny, only the width of two atoms.

Since diamonds are made of pure carbon, the researchers were able to take advantage of the uniform structure to create useful flaws in the diamonds, in the form of these NV centers. The scientists could remove one carbon atom in the diamond and replace it with a nitrogen atom. Next to the nitrogen atom, the scientists removed another carbon atom, creating an atomic-scale system consisting of a nitrogen atom with a hole next to it (thus, "nitrogen-vacancy"). These NV centers were each able to emit single photons and detect magnetic fields.

The researchers then pumped green laser light into the diamond, exciting the electrons in the NV centers. Once excited, these electrons are able to detect electromagnetic fields, including radio waves, and convert these signals into red light. From there, a photodiode could read the red light and convert it into a current, which was then translated into sound. A strong magnetic field around the diamonds allowed scientists to tune the device by changing the receiving frequency of the NV centers.

This atomic-scale radio receiver is capable of being tuned over 300 MHz. For context, FM radio usually falls between 87.5 MHz and 108 MHz, so this receiver, despite its size, is fully usable by usual standards.

While researchers used billions of NV centers to boost the signal, the receiver technically works with just one, though since only one photon is emitted at a time instead of a constant stream of red light, it is harder to detect. But the NV centers' ability to transmit information in the form of photons on an atomic scale makes it a promising candidate for quantum computation, which could one day use quantum physics to overcome the limitations of traditional binary computers. But for now, there are already plenty of potential uses for a nano-scale radio receiver embedded in diamond, one of the strongest materials in the world.

"Diamonds have these unique properties," Marko Loncar, the Tiantsai Lin Professor of Electrical Engineering at Harvard School of Engineering, said in a statement. "This radio would be able to operate in space, in harsh environments and even in the human body, as diamonds are biocompatible."

The researchers detailed the process for creating the world's smallest radio receiver in a paper published in the journal Physical Review Applied.