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Quantum controlled cluster states in an optical parametric oscillator with a structured light pump

Rafael F. Barros, G. B. Alves, Olivier Pfister, Antonio Zelaquett Khoury

Published Dec 30, 2020• 0 citations
OpenAlex

Abstract

We investigate the multipartite entanglement between spatial and spectral modes of an optical parametric oscillator pumped with a structured light field. When the pump beam is prepared in a second-order transverse mode, we show that the down-converted signal and idler fields are generated in a reconfigurable quadripartite entangled state of first-order modes. Our investigation is based both on separability criteria and a thorough analysis of the squeezing properties. Additionally, we demonstrate that large-scale entangled states can be produced and easily controlled by a pump field structured in both spatial and spectral domains. Our results pave the way for versatile cluster state engineering with structured light modes.

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We study the quantum state of twin photons generated by parametric down-conversion in a two-dimensional nonlinear photonic crystal, driven by a dual pump beam. The interplay between the grating of the ${\ensuremath{\chi}}^{(2)}$ nonlinear response and the transverse spatial modulation of the pump opens a rich scenario of possibilities for controlling the quantum state. We focus on a spatial resonance condition between the pump and the nonlinear grating, where a quadripartite entangled state is generated in proper light modes. The device is shown to implement the mixing of a pair of independent two-mode squeezed states onto four separate spatial modes, without the need of any external beam-splitter. Remarkably, both the squeezing parameters and the mixing coefficients can be reconfigured by modulating the relative phase and intensity of the two pumps, enabling thus the generation of a variety of quantum states in a single device.
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We report on our research effort to generate large-scale multipartite optical-mode entanglement using as few physical resources as possible. We have previously shown that cluster-and GHZ-type N-partite continuous-variable entanglement can be obtained in an optical resonator that contains a suitably designed second-order nonlinear optical medium, pumped by at most O \mathcal{O} O (N 2) fields. In this paper, we show that the frequency comb of such a resonator can be entangled in an arbitrary number of independent 2 × 2 and 2 × 3 continuousvariable cluster states by a single optical parametric oscillator pumped by just a few optical modes.
We show that scalable multipartite entanglement among light fields may be generated by optical parametric oscillators (OPOs). The tripartite entanglement existent among the three bright beams produced by a single OPO---pump, signal, and idler---is scalable to a system of many OPOs by pumping them in cascade with the same optical field. This latter serves as an entanglement distributor. The special case of two OPOs is studied, as it is shown that the resulting five bright beams share genuine multipartite entanglement. In addition, the structure of entanglement distribution among the fields can be manipulated to some degree by tuning the incident pump power. The scalability to many fields is straightforward, allowing an alternative implementation of a multipartite quantum information network with continuous variables.