World's smallest radio built from defects in diamonds

Scientists at Harvard have created the world's smallest radio receiver using atomic-scale defects in pink diamonds that may work anywhere from a spaceprobe to a pacemaker in a human heart. This tiny radio - whose building blocks are the size of two atoms - can withstand extremely harsh environments and is biocompatible.

The radio uses tiny imperfections in diamonds called nitrogen-vacancy (NV) centres. To make NV centres, researchers replace one carbon atom in a tiny diamond crystal with a nitrogen atom and remove a neighboring atom - creating a system that is essentially a nitrogen atom with a hole next to it. NV centers can be used to emit single photons or detect very weak magnetic fields. They have photoluminescent properties, meaning they can convert information into light, making them powerful and promising systems for quantum computing, phontonics and sensing.

Radios have five basic components - a power source, a receiver, a transducer to convert the high-frequency electromagnetic signal in the air to a low-frequency current, speaker or headphones to convert the current to sound and a tuner. In the device developed at Harvard University's John A Paulson School of Engineering and Applied Sciences (SEAS), electrons in diamond NV centers are powered, or pumped, by green light emitted from a laser. These electrons are sensitive to electromagnetic fields, including the waves used in FM radio.

When NV centre receives radio waves it converts them and emits the audio signal as red light. A common photodiode converts that light into a current, which is then converted to sound through a simple speaker or headphone. An electromagnet creates a strong magnetic field around the diamond, which can be used to change the radio station, tuning the receiving frequency of the NV centres. Researchers used billions of NV centres in order to boost the signal, but the radio works with a single NV centre, emitting one photon at a time, rather than a stream of light.

The radio is extremely resilient, thanks to the inherent strength of diamond. The team successfully played music at 350 degrees Celsius. "Diamonds have these unique properties. This radio would be able to operate in space, in harsh environments and even the human body, as diamonds are biocompatible," said Marko Loncar, professor at SEAS, who led the study. The study was published in the journal Physical Review Applied.