Optical experiments let researchers fully characterize the quantum transformations corresponding to photon creation and annihilation operators.
Quantum processors—devices designed to perform specific quantum transformations on a physical system—are at the core of novel protocols for quantum communication, measurement, and computing. Future quantum technologies will likely include different kinds of such devices, able to manipulate quantum states in accurately controlled ways. To guarantee the optimal overall performance of the system, the behavior of each quantum processor will have to be properly verified and completely characterized.
A quantum process is the operation performed by a quantum processor that transforms a quantum system’s state into a different one. For example, the well-known unitary operations correspond to reversible, deterministic transformations such as rotation of a photon’s polarization. But quantum processes also encompass more general transformations and can therefore also describe the coupling of the system with the environment and the action of quantum measurements [1, 2].
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