Disclosed herein are qubit-detector die assemblies, as well as related computing devices and methods. In some embodiments, a die assembly may include: a first die having a first face and an opposing second face, wherein a plurality of active qubit devices are disposed at the first face of the first die; and a second die, mechanically coupled to the first die, having a first face and an opposing second face, wherein a plurality of quantum state detector devices are disposed at the first face of the second die; wherein the first faces of the first and second dies face each other.