The Quantum Tunnel is an inter-dimensional gateway that is capable of transporting individuals to and from the Quantum Realm. Created in the 1980s by Hank Pym, Bill Foster and Elihas Starr, it was used by the latter in an attempt to harness quantum energy; however, the tunnel exploded, causing the energy to be absorbed by his daughter, Ava.
A second version of the tunnel was created in 2018 by Hank Pym and Hope van Dyne to rescue Janet van Dyne from the Quantum Realm, while a third version, outfitted into Luis' Van, was used to send Scott Lang into the realm in order to acquire quantum energy to heal Ava. After Lang was freed from the Quantum Realm, the tunnel was used by Bruce Banner in an attempt to send Lang through time.
In order to reverse the effects of the Snap, a fourth tunnel was created in 2023 by Tony Stark and Rocket Raccoon in order to send the Avengers back in time to acquire the six Infinity Stones. The tunnel was later used by the 2014 version of Nebula, who used it to transport the Sanctuary II into the future, destroying the tunnel in the process.
S.H.I.E.L.D. scientists Elihas Starr, Hank Pym and Bill Foster worked together on harnessing the powers of the Quantum Realm, an alternate dimension that Pym discovered. However, Elihas attempted to steal Pym's plans, resulting in Pym firing and discrediting Elihas, forcing him and his family to go into hiding.
Sometime later, Elihas managed to recreate a Quantum Tunnel, planning to regain his reputation. However, the new Tunnel malfunctioned, causing an explosion that killed Elihas and his wife Catherine Starr, also granting his daughter Ava powers.
After Ant-Man's escape from the Quantum Realm in 2015, Hank Pym was inspired to recreate the Quantum Tunnel in order to save his lost wife Janet van Dyne, and brought his daughter Hope van Dyne in on the project. Being forced to go into hiding due to their association with Scott Lang for his involvement in the Clash of the Avengers, they built the Quantum Tunnel inside the Mobile Laboratory.
When Hank and Hope tested the Quantum Tunnel, it briefly remained stable before overloading. Five minutes after, they received a call from Lang, who claimed to have experienced a dream where he saw himself as Janet. Hypothesizing that Lang had become quantum entangled with Janet when he was last in the Quantum Realm and that she placed a message in his mind as a means of finding her, and opening the Tunnel triggered it, Hank sent Hope to retrieve Lang from his house arrest. Once Lang described his dream, Hank and Hope realized he was living the memory of how Janet and Hope used to play hide-and-seek, which was proof that Janet was indeed alive in the Quantum Realm. They then promptly set off to recover a part from Sonny Burch to keep the Tunnel from overloading.
Despite interference from Burch and Ghost, they were able to get the part. Upon growing the Mobile Laboratory in the forest, they activated the Quantum Tunnel, allowing Janet to take control of Lang's body, who gives them a precise location to find her, but warns that they only have two hours before the unstable nature of the realm separates them for a century.
After the rescue of Janet van Dyne, a smaller, more portable Quantum Tunnel was built and housed inside Luis' Van. Lang used the Tunnel to go into the Quantum Realm and harvest more quantum particles for Ghost but right before he was brought back the Snap occurred, eradicating everyone who was operating the tunnel and leaving Lang trapped in the Quantum Realm. The van was taken to a warehouse were it remained for five years until a rat accidentally turned on the Quantum Tunnel again, returning Lang to Earth. Lang subsequently transported the Quantum Tunnel to the New Avengers Facility, where he pitched the idea of using the Quantum Realm to travel back in time and retrieve the Infinity Stones to undo the Snap. Lang then acted as test subject under the supervision of the Hulk as he used the Quantum Tunnel to travel back a week. However, upon his return, Lang had physically regressed to a teenager, forcing Hulk to send him back, only to turn Lang into an old man and then a baby before restoring his normal age as Black Widow cut the power.
The Quantum Tunnel managed to survive the Attack on the New Avengers Facility by an alternate version of the Sanctuary II intact. During the Battle of Earth, Ant-Man and the Wasp managed to reactivate the Quantum Tunnel in the hopes of returning the Infinity Stones to their proper times before Thanos could use them to destroy the universe. Unfortunately, before Captain Marvel could reach Luis' van with the Nano Gauntlet, Thanos threw his Double-Edged Sword at the Quantum Tunnel, destroying it.
A newer, more sophisticated Quantum Tunnel was later built by the Avengers in order to execute the Time Heist in an effort to undo the Snap. The Avengers' Quantum Tunnel was destroyed when the Sanctuary II emerged from it.
A final Quantum Tunnel was built following Tony Stark's death so that Steve Rogers could return all the Infinity Stones and Mjølnir to their respective alternate timelines in order to prevent catastrophic changes to those timelines' future. Rogers, however, did not return, instead opting to stay in the past to live the life with Peggy Carter that he had originally missed out on.