qCraft is not a simulation of quantum physics, but it does provide ‘analogies’ that attempt to show how quantum behaviors are different from everyday experience, allowing players to create structures and devices that exhibit Minecraft versions of quantum properties like observer dependence, superposition and entanglement.
This wiki provides documentation of the features and capabilities of the mod. For a thorough tour of what the mod can do, check out this overview from Direwolf20. You may also want to check out the qCrafting series of videos on the mod's official YouTube Channel.
This video by Minecraft Spotlight also provides a great quick overview: