States and Processes

Saleh Rahimi-Keshari, T. Kiesel, W. Vogel +3 more

We propose a definition of nonclassicality for a single-mode quantum-optical process based on its action on coherent states. If a quantum process transforms a coherent state to a nonclassical state, it is verified to be nonclassical. To identify nonclassical processes, we introduce a representation for quantum processes, called the process-nonclassicality quasiprobability distribution, whose negativities indicate nonclassicality of the process. Using this distribution, we derive a relation for predicting nonclassicality of the output states for a given input state. We experimentally demonstrate our method by considering the single-photon addition as a nonclassical process and predicting nonclassicality of the output state for an input thermal state.

Daniel Linnemann

Lee A. Rozema, Ardavan Darabi, Dylan H. Mahler +2 more

Quantum process tomography requires a set of input states sensitive to the unknown process. We experimentally generate a class of 4-photon states and compare their sensitivity to that of coherent states to a decohering process.

Bruce Mills

Nicolás Quesada, Agata M. Brańczyk, Daniel F. V. James

Incompletely characterized processes can be used for state tomography. We formalize this idea and show how to chose processes that ensure invertibility for the unknown state, as well as the unknown process parameters.