Demonstration of a programmable source of two-photon multiqubit entangled states

TL;DR

This paper presents a novel, programmable source for generating high-fidelity two-photon multipartite entangled states using spatial light modulation, enabling flexible quantum state engineering with low-power lasers.

Contribution

It introduces a new method combining spatial light modulation with spontaneous parametric downconversion to produce arbitrary multi-qubit entangled states.

Findings

Successfully generated two-photon three-qubit linear cluster states

Achieved high fidelity with low-power diode laser pump

Demonstrated programmable phase control between degrees of freedom

Abstract

We suggest and demonstrate a novel source of two-photon multipartite entangled states which exploits the transverse spatial structure of spontaneous parametric downconversion together with a programmable spatial light modulator (SLM). The 1D SLM is used to perform polarization entanglement purification and to realize arbitrary phase-gates between polarization and momentum degrees of freedom of photons. We experimentally demonstrate our scheme by generating two-photon three qubit linear cluster states with high fidelity using a diode laser pump with a limited coherence time and power on the crystal as low as 2.5$mW.