Ultra‑Sensitive Graphene Microwave Photon Sensor

A microwave radiation sensor with 100,000 times higher sensitivity than currently available commercial sensors has been developed. The bolometer was fabricated by exploiting the giant thermal response of graphene to microwave radiation. The microwave bolometer is capable of detecting a single microwave photon — the smallest amount of energy in nature.

The graphene bolometer sensor detects electromagnetic radiation by measuring the temperature rise as the photons are absorbed into the sensor. Graphene is a two-dimensional, one-atom-layer-thick material. The research team achieved a high bolometer sensitivity by incorporating graphene in the microwave antenna.

A key innovation in this advancement is to measure the temperature rise by superconducting Josephson junction while maintaining a high microwave radiation coupling into the graphene through an antenna. The coupling efficiency is essential in high-sensitivity detection. A Josephson junction is a quantum mechanical device made of two superconducting electrodes separated by a barrier (thin insulating tunnel barrier, normal metal, semiconductor, ferromagnet, etc.).

In addition to being thin, the electrons in graphene are also in a very special band structure in which the valence and conduction bands meet at only one point known as Dirac point. The density of states vanishes there; when the electrons receive the photon energy, the temperature rise is high while the heat leakage is small.

With increased sensitivity of bolometer detectors, this research has found a new pathway to improve the performance of systems detecting electromagnetic signals such as radar, night vision, LiDAR (Light Detection and Ranging), and communication. It could also enable new applications such as quantum information science, thermal imaging, and the search of dark matter.