Quantum measurement as a tool for probabilistic transformation of quantum light states

Specific properties of quantum measurements (backaction on the measured object, randomness of the outcomes) lead to “hidden” character of quantum information and hinder investigation of quantum systems. On the other hand, inevitable influence of the measuring device on the quantum system can serve as an instrument for steering it to a useful target state. The talk is devoted to that aspect of quantum measurements: special measurement types capable of creating various target states; general ideas of measurement-induced control of quantum states; interpretation of dissipative (non-unitary) dynamics of quantum systems in terms of continuous measurements and its usage for generation of non-classical quantum-optical states. Namely, a class of “elimination” measurements is defined, discussed, and shown to be efficient for quantum light state manipulation. Further, the idea is extended to the field of quantum imaging and an approach to conditional enhancement of photonic state sensitivity to the illuminated object sub-Rayleigh features is proposed. The close connection between dissipative non-unitary dynamics and measurement-induced steering of a quantum state makes the concept of “elimination” measurements also fruitful for description of an optical system subjected to nonlinear coherent loss and showing its capability of generating sub-Poissonian quantum-optical states.