Matter bridge

A Matter bridge is a device which draws energy from a parallel universe.

Project Arcturus
Project Arcturus was an attempt by the Ancients to extract zero point energy from their own universe.

Jeannie Miller's bridge
In 2006, Jeannie Miller developed calculations, which helped solve the problems that plagued Project Arcturus. Instead of trying to draw zero point energy from our own universe and release hazardous exotic particles, McKay planed to draw energy from a parallel universe via a matter bridge so the exotic particles would be vented into the hopefully uninhabited parallel universe instead. Working together, McKay and Jeannie managed to resurrect Project Arcturus and successfully activated it without releasing exotic particles.

However, while being tested, a Rodney McKay from a parallel universe materialized inside the containment chamber. Alternate McKay explained to the Atlantis team that he was sent to this universe in order to warn them that his universe was slowly being destroyed by the exotic particles being created by Project Arcturus, and the project was immediately shut down to prevent any more damage. However, even though Project Arcturus had been shut down, the matter bridge was still open and Rod's universe was still being destroyed.

McKay realized that there is an alternate way to close the matter bridge without having to destroy either universe, which involved using massive amounts of energy to forcibly close the matter bridge using the ZPM. They successfully closed the bridge, but McKay kept the energy running in order to give Rod time to beam back to his own universe, draining Atlantis' only ZMP in the process.