Researchers Send Twin Photons 7 Kilometers Across Brazil’s Guanabara Bay

Insider Brief

• Brazilian researchers sent one photon from each twin pair 7 kilometers across Guanabara Bay while detecting the other at the source.
• The experiment recorded 7,000 coincident detections in five seconds despite atmospheric turbulence and other sources of signal loss.
• Researchers have not yet confirmed that entanglement survived the journey and plan to test the photons’ polarization next.
• Image: Experimental setup at UFF, in Niterói, from where photons are sent towards CBPF, in Rio de Janeiro. The optical system includes the light source and the telescope used to project the beam through the 7 kilometers of atmosphere over Guanabara Bay (photo: André Luiz da Silva Santos Junior)

PRESS RELEASE — José Tadeu Arantes | Agência FAPESP — Researchers at Fluminense Federal University (UFF) have taken an important step toward quantum communication and the creation of an ultra-secure internet. They generated pairs of “twin photons,” or particles of light, and showed that the photons maintained a strong correlation even after one traveled about 7 kilometers through the air across Guanabara Bay in Rio de Janeiro. While one photon remained at the UFF laboratory in Niterói, its “twin” crossed the bay to Urca.