A better source of entangled photons for quantum imaging

Entangled photons tend to arrive at the same position simultaneously. This is the basis of quantum imaging: In a type of imaging called quantum image distillation, quantum light is distinguished from classical light by separating spatially correlated photons from uncorrelated photons.

One of the biggest limitations to quantum imaging is the efficiency of generating entangled photons. Yoshimura et al. replaced the standard beta-barium borate (BBO) crystals — typically used to create entangled photons — with bismuth triborate (BiBO), which is known to efficiently generate entangled photon pairs but had not been previously tested for use in quantum imaging.

“Entangled photons are produced when a single photon from a laser splits into a pair of twin photons, but this process is extremely inefficient,” said author Naru Yoneda. “In quantum imaging, entangled photons are used to illuminate the object being observed. Therefore, if the illumination light is too weak, it becomes difficult to observe the object properly.”

In testing BiBO crystals as the light source for quantum image distillation — aptly, by illuminating images of a dead and alive cat with quantum and classical light — the researchers were able to separate the quantum and classical images with a contrast nearly six times larger than with BBO crystals.

Though quantum image distillation was first demonstrated in 2019, Yoneda said he was “still somewhat skeptical until we actually performed the experiment ourselves.”

“When we were able to realize quantum image distillation using BiBO, I was filled with both surprise and joy,” he said.

The group is working to develop a microscope for optogenetics using entangled two-photon absorption, which will require a bright source of entangled photons. They hope to apply the current work in their upcoming device.

Source: “Enhancing quantum imaging efficiency by BiBO crystal-based entangled light source,” by Kanako Yoshimura, Naru Yoneda, and Osamu Matoba, AIP Advances (2026). The article can be accessed at https://doi.org/10.1063/5.0314450 .