A cryo-arithmetic engine is a type of quantum computer employed by the Conjoiners. When certain algorithms are executed on processors of this architecture, it leads to a local violation of the Second law of thermodynamics -- the computer gets colder instead of hotter.
Such engines were utilized in Conjoiner asteroid factories as heat sinks, where their calculations drained away the excess heat produced. Cryo-arithmetic engines were also used by certain Conjoiner lighthuggers; they cooled the exterior of the ship to the temperature of space, making the vessels difficult to detect.
The technology was later successfully miniaturized with aid from Aura, Ana Khouri's daughter. The resulting device was the size of an apple.