Quadripartite entangled state from cascaded second-harmonic generation

Abstract

A generation system of continuous-variable (CV) quadripartite entangled state based on two cascaded secondharmonic generation (SHG) cavities below the threshold is investigated. Two reflected fundamental beams of the first cavity, the reflected second-harmonic beam and the output fourth-harmonic beam of the second cavity are proved to be entangled, and the dependence of the entanglement degree on the normalized frequency, pump parameter, fourth-harmonic loss parameter, and second-harmonic loss parameter is also analyzed. Due to the fact that the cavity parameters and the nonlinear crystals of the two SHG cavities can be freely chosen, the practicality of the proposed protocol is relatively perfect and the system can also be extended to the preparation of multicolor entangled states for a quantum network.

Quadripartite entanglement from coupled type I second harmonic generation

“…Simpler schemes, where tripartite entanglement exists in the three output fields directly from above threshold optical parametric oscillator (OPO) [13] or type II SHG [14,15], have been predicted and experimentally confirmed [16]. Quadripartite entanglement generated from cascaded second-harmonic generation [17] and in an opto-mechanical system are also suggested [18]. However, for quadripartite entanglement, to our knowledge, quasiperiodic optical superlattice is as an important candidate [19,20].…”