Optimal quantum operations at zero energy cost

Understand

Quantum technologies are developing powerful tools to generate and manipulate coherent superpositions of different energy levels.

• Envisaging a new generation of energy-efficient quantum devices, here we explore how coherence can be manipulated without exchanging energy with the surrounding environment.
• We start from the task of converting a coherent superposition of energy eigenstates into another.
• We identify the optimal energy-preserving operations, both in the deterministic and in the probabilistic scenario.