Algorithmic cooling

Algorithmic cooling is an algorithmic method for transferring heat (or entropy) from some qubits to others^[1] or outside the system and into the environment, which results in a cooling effect. This method uses regular quantum operations on ensembles of qubits, and it can be shown that it can succeed beyond Shannon's bound on data compression.^[2] The phenomenon is a result of the connection between thermodynamics and information theory.

The cooling itself is done in an algorithmic manner using ordinary quantum operations. The input is a set of qubits, and the output is a subset of qubits cooled to a desired threshold determined by the user. This cooling effect may have usages in initializing cold (highly pure) qubits for quantum computation and in increasing polarization of certain spins in nuclear magnetic resonance. Therefore, it can be used in the initializing process taking place before a regular quantum computation.