Aunque la velocidad de grupo de un pulso supere la velocidad de la luz, la información va a su ritmo respetando el límite de velocidad einsteniano.
Gauthier’s team found that information encoded in a pulse travelling through a gas of potassium atoms takes longer to be detected than information in a pulse travelling through a vacuum at speed c. Even if the pulse’s group velocity far outstrips the speed of light, the information velocity can never exceed c.
In other words, the pulse arrives sooner but takes longer to announce its arrival.