Quantum feedback


Quantum feedback or quantum feedback control is a class of methods to prepare and manipulate a quantum system in which that system's quantum state or trajectory is used to evolve the system towards some desired outcome. Just as in the classical case, feedback occurs when outputs from the system are used as inputs that control the dynamics. The feedback signal is typically filtered or processed in a classical way, which is often described as [|measurement based feedback]. However, quantum feedback also allows the possibility of maintaining the quantum coherence of the output as the signal is processed, which has no classical analogue.

Measurement based feedback

In the closed loop quantum control, the feedback may be entirely dynamical. This is named Coherent Control. Alternatively, the feedback may be entirely information theoretic insofar as the controller gains information about the plant due to measurement of the plant. This is measurement-based control.

Coherent feedback