Quantum Optics Seminar by Elizabeth Agudelo Ospina – Niels Bohr Institute - University of Copenhagen

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Quantum Optics Seminar by Elizabeth Agudelo Ospina

For the description and analysis of physical systems is fundamental the characterization and the deep understanding of the nonclassicality of quantum states. At present one could define quantumness by different criteria, including negativities of the P function, entanglement, or quantum discord.The density operator of the physical system is expressed in terms of the P function, P(\alpha), in diagonal form in the basis of the coherent states. The state is referred to as a nonclassical one if P(\alpha) has the properties of a classical probability density. In this case, the state represents a classical mixture of coherent states. In general the P function exhibit negativities and it can be highly singular too. Due to its singularities, the P function is in general not experimentally accessible and, hence, of limited practical value.For the single-mode case, nonclassicality quasiprobabilities (QPs), P_{Ncl}, have been introduced, which are regularized versions of the highly singular P function. For any nonclassical single-mode state, they show negativities and can be directly obtained from experimental data.
Hence P_{Ncl} is a powerful tool for the full experimental characterization of quantum effects of single-mode fields. This QP distribution can be generalized to multimode systems. Beyond the multimode scenario, space-time dependent quantum correlations can be characterized by P functionals, leading to nonclassicality conditions for general field correlation functions.
We generalize the regularization method via nonclassicality filtering. On the basis of the multimode Glauber-Sudarshan P function, we establish a family of nonclassicality QPs for multipartite quantum correlations.
This family is necessary and sufficient to detect any nonclassical multipartite P function and can be directly applied in experiments. Most importantly, it is accessible in experiments and it uncovers general quantum correlations.