Single-photon terahertz detectors without cryogenic conditions

Terahertz (THz) radiation, a frequency band sitting between infrared and microwave bands, enables a wide range of applications spanning from astronomy to biomedicine. However, ultrahigh-sensitive THz detection at the single-photo level remains elusive. Realizing THz technologies at this resolution would push the scope of far-infrared spectroscopy and communication technologies; therefore, it has attracted significant attention in research.

The largest barrier to real-world applications of THz radiation is its operating temperatures, as current THz technologies require cryogenic cooling. To address this “THz gap,” Li et al. achieved continuous single-photon detection at room temperature.

“THz in a frequency range of 10^12±1 Hz has been considered as one of the top ten technologies that will change the world of the future,” said author Jiteng Sheng. “We have developed the room temperature THz detector at single-photon levels, for the first time, based on nonlinear wave mixing in thermal Rydberg atomic vapor.”

Through a six-wave mixing process in thermal Rydberg gas, the authors upconverted low-energy THz photons to high-energy photons at room temperature. This was possible due to a combination of multilevel atomic coherence and large Rydberg dipole moments, which allowed for efficient nonlinear interactions. The noise equivalent power of this single-photon THz detector exceeded state-of-the-art highly sensitive room-temperature THz detectors by four orders of magnitude.

The authors plan to continue exploring chip-scale applications of THz single-photon detectors.

“Our next step is to utilize this novel room temperature THz single-photon detector for practical applications, such as THz imaging and THz communication,” said Sheng.

Source: “Room temperature single-photon terahertz detection with thermal Rydberg atoms,” by Danyang Li, Zhengyang Bai, Xiaoliang Zuo, Yuelong Wu, Jiteng Sheng, and Haibin Wu, Applied Physics Reviews (2024). The article can be accessed at https://doi.org/10.1063/5.0219879 .