Quantum items are a new type of cosmetics coming in Patch 10.1.5 that teach you appearances from the past, including weapons and armor.
The latest Patch 10.1.5 Build 49908 adds quantum items. While we don’t know exactly how they will work, the tied spells indicate they will teach you item appearances from the past. Maybe this is Blizzard’s new way of bringing back removed items like the ones from Zul’Gurub or Naxxramas in Patch 10.1.5 and instead of having X items you must collect, there will be just 1 sort of “token” with many appearances tied to it.
The following Quantum items have been added so far: