Quantum Instrument - Description

Description

Usually it is implemented as a weighted collection of completely positive maps the sum of which is trace preserving.

Quantum Instrument: collection acts as: \rho^{AB} \rightarrow \tilde{\rho}^{AA'B} := \sum_k \mathcal{E}_k \left( \rho^{AB} \right)\otimes \vert k \rangle \langle k\vert^{A'}

A quantum instrument is more general than a quantum operation because it records the outcome k of which operator acted on the state.

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