On Realization of Back-Action-Evading Measurements and Quantum Non-Demolition Variables via Linear Systems Engineering
This work provides a systematic engineering approach for quantum measurement and control, relevant to experimentalists in quantum optics and quantum information.
The paper establishes a framework for realizing back-action-evading measurements and quantum non-demolition variables in linear quantum systems, identifying key conditions and designing coherent feedback for non-compliant systems.
We establish a framework for realizing back-action-evading (BAE) measurements and quantum non-demolition (QND) variables in linear quantum systems. The key condition, a purely imaginary Hamiltonian with a real or imaginary coupling operator, enables BAE measurements of conjugate observables. Symmetric coupling further yields QND variables. For non-compliant systems, coherent feedback is designed to engineer BAE measurements. Crucially, the QND interaction condition simultaneously ensures BAE measurements and promotes the coupling operator to a QND observable.