From left to right, Roshan Krishna Kumar, Frank Koppens and Krystian Nowakowski in their lab at ICFO.
Single photons in the mid-infrared can reveal faint galaxies or carry fragile quantum signals across space. They are valuable in astronomy, quantum communication, and even medical imaging.
But detecting them is not easy.
Light in this range is often extremely faint. Capturing it has usually meant using large cryogenic systems cooled to below 1 Kelvin.
These systems are expensive, consume a lot of energy, and are hard to integrate into modern photonic circuits.
Now, an international team led by ICFO researchers has found a way to detect such photons at about 25 Kelvin, far above the limits of conventional designs.
Their results have already attracted the interest of the European Space Agency.
Overcoming cryogenic limits
The new detector is built from stacked two-dimensional materials just one atom thick. At its core is bilayer graphene, sandwiched between layers of hexagonal boron nitride. Aligning the materials with the needed precision was difficult.
Early attempts had only a 50 percent success rate, but the team improved the process through careful design and experience from earlier work.
The breakthrough comes from a property called bistability. This allows a system to remain in two stable states under the same conditions.
A slight twist between the graphene and boron nitride layers produces a moiré pattern, changing how electrons behave and enabling this effect.
ICFO senior author Frank Koppens said the light sensitivity appeared unexpectedly during experiments with twisted 2D materials, prompting the team to investigate further.
New detection mechanism
The device operates close to an electrical tipping point. Co-author Krystian Nowakowski compared it to stacking straws on a table until one more straw causes it to collapse.
Here, a single photon acts as that last straw, switching the device from one stable state to another.
This approach differs from both superconducting and semiconductor-based detectors. It can pick up long-wavelength photons without needing ultra-low temperatures.
Co-supervisor Roshan Krishna Kumar said the design “breaks the fundamental limits that held previous technologies back.”
Better detection of mid-infrared single photons could help astronomers study fainter and more distant objects.
It could improve long-distance quantum communications by reducing noise and signal loss. Medical imaging systems could also benefit from greater sensitivity.
The ICFO team plans to make the device more compact and push its operating temperature higher. Those factors will decide whether the detector can move from lab experiments to practical use.
As co-author Pablo Jarillo-Herrero noted, the findings highlight the potential of moiré quantum devices for both advancing fundamental science and enabling new technologies.
The study is published in the journal Science.
- What is single photon detection?Single photon detection is the ability to sense the smallest possible unit of light. In fields like astronomy and quantum communication, detecting single photons helps capture extremely faint signals with high precision.
- Why is mid-infrared photon detection important?Mid-infrared photons can reveal information that visible light cannot, such as details of distant galaxies or secure quantum signals. This range is also useful in medical imaging for detecting subtle changes in biological tissues.
- What role do 2D materials play in advanced detectors?Two-dimensional materials, such as bilayer graphene, are only one atom thick and have unique electronic properties. They enable compact, highly sensitive detectors that can operate at higher temperatures than traditional cryogenic systems.
