Twisted 2D Materials Enable A Breakthrough In Single-Photon Detection

Dr Roshan Krishna Kumar participated in a study led by ICFO that overcame a long-standing barrier in photonics, developing an ultra-sensitive detector based on twisted 2D materials capable of detecting individual photons, even in the infrared spectrum.

A photon is the most basic unit of light—an elementary particle that carries energy in the form of electromagnetic radiation. Detecting individual photons in the infrared spectrum is a major challenge in fields such as quantum computing, quantum communication, and astronomy. Until now, achieving this has required expensive cryogenic systems capable of operating at extremely low temperatures, which significantly limit practical applications. Now, an international team led by scientists at ICFO, and including Dr Roshan Krishna Kumar from the ICN2 Ultrafast Dynamics in Nanoscale Systems Group, has discovered a new way to overcome this obstacle using two-dimensional (2D) materials.

The study, published in the journal Science, describes the development of an ultra-sensitive detector that can identify single photons in the visible and mid-infrared regions of the electromagnetic spectrum. Remarkably, the device operates at temperatures as high as 25 kelvin (-248°C), which is significantly higher than the temperatures required by conventional technologies.

The device comprises a bilayer of graphene covered by a second 2D material, hexagonal boron nitride (hBN). The two materials were aligned with great precision to form a small angle, which enables the moiré effect to emerge. This effect has been widely studied in 2D materials and greatly modifies their electrical and magnetic properties.

However, the study's results revealed another key property of this structure: bistability. This phenomenon enables a system to remain stable in two distinct states under the same external conditions, much like a switch that can be either on or off. The scientists observed that the device could abruptly switch between these states after absorbing a single photon, enabling the precise detection of single photons.

Although there is still a long way to go in optimising this technology, such as enabling the system to operate at higher temperatures, these findings could make a significant contribution to the development of next-generation quantum devices and play a key role in fields such as observational astronomy and medical diagnostics.