A major advancement has shaken the telecommunications world. Researchers have successfully transmitted entangled photons through a commercial optical fiber in a downtown area while the same fiber was carrying Internet data. This achievement marks the first time quantum technology and classical Internet traffic have coexisted on a production telecommunications network. Until now, this was considered impossible due to the fragility of quantum signals, which can be destroyed by even slight interference. Previous research suggested deploying a fiber optic network entirely dedicated to quantum communications, which would represent a colossal infrastructure cost for operators and companies. Scientists from Northwestern University in the United States have demonstrated that this is not necessary. They transmitted quantum information between two locations over 24 kilometers of active fiber, simultaneously with classical Internet traffic equivalent to 36 terabits per second. Nearly 95% of fidelity was preserved. This means that tomorrow's network can be based on today's fiber, avoiding the need to double the networks and thus significantly reducing costs. To achieve this, the research team required a perfect mastery of spectro-temporal engineering. The idea is to make an ant travel through a herd of elephants without being crushed, as explained by the researchers. To succeed, the team shifted the quantum signals to the O band of the light spectrum, allowing classical traffic to occupy the usual C band. Precision filters were used to eliminate optical noise. To identify pairs of entangled photons at a distance, the two sites were synchronized to the picosecond using a system called White Rabbit. This extreme precision guarantees the reliability of communications in a saturated environment. This discovery marks the true beginning of quantum teleportation. Quantum entanglement allows two particles to be linked at a distance, offering unprecedented perspectives for cybersecurity and ultra-fast exchanges. By proving that this distribution works under real conditions, the team opens the way to the second stage, the transfer of information by quantum teleportation.