Engineering multipartite entanglement in nonlinear photonic crystals
Prof. Alessandra Gatti, Università dell’ Insubria, Como, Italy
Leuchs-Russell Auditorium, A.1.500, Staudtstr. 2
This seminar analyzes the quantum state of twin-photon generated by parametric down-conversion in a nonlinear photonic crystal (NPC), with a periodic modulation of the nonlinear susceptibility in 2 dimensions. The peculiarities of this source derive from the multiple possibilities of quasi-phase matching, supported by the multiplicity of noncollinear vectors of the 2D pattern, and from the existence of shared modes characterized by a tripartite coupling, where interesting path-entangled quantum states can be realized.
The interplay between the pump spatial degrees of freedom and the nonlinear pattern enriches the possibilities: as recently demonstrated , by properly modulating the transverse phase of the pump, a peculiar resonance effect takes place with a sudden boosts of the intensities of shared modes. At the same time, the tripartite entanglement turns into a four-mode entangled state, dominated by the Golden Ratio of the segment . The curious appearance of this famous number will be discussed in connection with an analogy with the Fibonacci series. A transverse modulation of the pump intensity opens the relevant possibility of engineering the state . In condition of spatial resonance we will show that the source enables a flexible interference of squeezed states, without the need of an external beam splitter, where both the squeezing amplitudes and mixing coefficients can be reconfigured by acting on the pump pattern.
 O.Jedrkiewicz, A. Gatti, E. Brambilla, M. Levenius, G. Tamošauskas, K. Gallo, Sci. Rep. 8, 1 (2018).
 A. Gatti, E. Brambilla, K. Gallo, O. Jedrkiewicz, Phys. Rev. A 98, 053827 (2018).
 E. Brambilla and A. Gatti, Opt. Expr. 27,30233 (2019)