Copper "headphones" Improve Atomic Radio Reception by a Factor of 100

Scientists at the National Institute of Standards and Technology (NIST) have increased the sensitivity of their atomic radio receiver a hundredfold by enclosing the small glass cylinder of cesium atoms inside what looks like custom copper “headphones.”

The structure — a square overhead loop connecting two square panels — boosts the incoming radio signal, or electric field, applied to the gaseous atoms in the flask (known as a vapor cell) between the panels. This enhancement enables the radio receiver to detect much weaker signals than before. The demonstration is described in a new paper that was published in the journal Applied Physics Letters.

The headphone structure is technically a split-ring resonator, which acts like a metamaterial — a material engineered with novel structures to achieve unusual properties. “We can call it a metamaterials-inspired structure,” NIST project leader Chris Holloway said.

Researchers at NIST previously demonstrated the atom-based radio receiver. An atomic sensor has the potential to be physically smaller and work better in noisy environments than conventional radio receivers, among other possible advantages.

The vapor cell is about 14 millimeters (0.55 inches) long with a diameter of 10 mm (0.39 inches), roughly the size of a fingernail or computer chip, but thicker. The resonator’s overhead loop is about 16 mm (0.63 inches) on a side, and the ear covers are about 12 mm (0.47 inches) on a side.

The NIST radio receiver relies on a special state of the atoms. Researchers use two different color lasers to prepare atoms contained in the vapor cell into high-energy (“Rydberg”) states, which have novel properties such as extreme sensitivity to electromagnetic fields. The frequency and strength of an applied electric field affect the colors of light absorbed by the atoms, and this has the effect of converting the signal strength to an optical frequency that can be measured accurately.