Researchers of CEFOP contribute to the understanding of the concept of complementarity

Complementarity presents open questions and is important in the interpretation of quantum mechanics. Therefore, it is an active area of theoretical and experimental research.

An important study in the world took place in the group of Optics and Quantum Information of the Center, along with the Department of Physics of Universidade Federal de Minas Gerais in Brasil. The investigation, which began in June 2009, resulted in a recently published article in the journal Physics Review A, under the title “Interference and Complementarity for two-photon hybrid entangled states”. In this article, it was reported the results of theoretical and experimental studies about a complementarity relation between the visibilities of the patterns of one- and two-photon observed when a pair of photons is in a state known as hybrid photonic state, which is a state that has entanglement between two different degrees of photons (DOFs). In this case, the investigation involved the transverse-spatial and polarization DOFs of the photon pair.

According to the investigator, “The article presents the results of the study of one- and two-photon interference patterns that can be observed when preparing a two-photon electromagnetic field in a hybrid entangled state, allowing us to study the relationship of complementarity between the visibility of these patterns “.

OuvirIn CEFOP’s lab, hybrid entangled states are generated by the suitable manipulations of the state of a pair of photons generated by means of the non-linear optical process known as spontaneous parametric down-conversion (SPDC). In this process, one photon from the laser interacts with a nonlinear crystal. As the result, two entangled photons are generated. Ler foneticamente

The work has begun with the development of a theoretical description, which meant the calculation and analysis of the one- and two-photon probability distributions for a state like that. This theoretical work showed that the patterns for entanglement between two different DOFs should obey a complementarity relation that was already observed for entangled states that envolve just one DOF. After this step, a series of measurements was performed in order to test the theory and the complementarity relation, resulting in the confirmation of  the predictions.

Nogueira said that one of the possible extensions of this work is the study of complementarity in the interference patterns of larger quantum systems, based on the fact that the CEFOP’s lab is researching ways to generate hybrid entangled states of higher orders.

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