Remotely preparing optical Schr\"odinger cat states via homodyne detection in nondegenerate triple-photon spontaneous downconversion

TL;DR

This paper demonstrates remote preparation of optical Schrödinger cat states and entangled states via homodyne detection in nondegenerate triple-photon spontaneous downconversion, revealing nonlinear quantum steering effects and non-Gaussian nonclassical features.

Contribution

It introduces a method to generate large Schrödinger cat states and entangled states remotely using NTPSD and homodyne detection, highlighting nonlinear quantum steering effects.

Findings

Large Schrödinger cat states can be generated remotely.

Two-photon Bell entangled states can be produced via homodyne detection.

Nonlinear quantum steering underpins the ability to remotely prepare these states.

Abstract

Optical downconversion is a key resource for generating nonclassical states. Very recently, direct nondegenerate triple-photon spontaneous downconversion (NTPSD) with bright photon triplets and strong third-order correlations has been demonstrated in a superconducting device (2020 Phys. Rev. X 10 011011). Besides, linear and nonlinear tripartite entanglement in this process have also been predicted (2018 Phys. Rev. Lett. 120 043601; 2020 Phys. Rev. Lett. 125 020502). In this paper, we consider the generation of nonclassical optical quantum superpositions and investigate nonlinear quantum steering effects in NTPSD.We find that large-size Schr\"odinger cat states of one downconverted mode can be achieved when the other two modes are subjected to homodyne detection. Also, a two-photon Bell entangled state can be generated when only one mode is homodyned.We further reveal that such ability of remote state steering originates from nonlinear quantum steerable correlations among the triplets. This is specifically embodied by the seeming violation of the Heisenberg uncertainty relation for the inferred variances of two noncommutating higher-order quadratures of downconverted modes, based on the outcomes of homodyne detection on the other mode, i.e., nonlinear quantum steering, compared to original EPR steering. Our results demonstrate non-Gaussian nonclassical features in NTPSD and would be useful for the fundamental tests of quantum physics and implementations of optical quantum technologies.