Direct transfer of classical non-separable states into hybrid entangled two photon states

Abstract

Hybrid entangled states, having entanglement between different degrees-of-freedom (DoF) of a particle pair, are of great interest for quantum information science and communication protocols. Among different DoFs, the hybrid entangled states encoded with polarization and orbital angular momentum (OAM) allow the generation of qubit-qudit entangled states, macroscopic entanglement with very high quanta of OAM and improvement in angular resolution in remote sensing. Till date, such hybrid entangled states are generated by using a high-fidelity polarization entangled states and subsequent imprinting of chosen amount of OAM using suitable mode converters such as spatial light modulator in complicated experimental schemes. Given that the entangled sources have feeble number of photons, loss of photons during imprinting of OAM using diffractive optical elements limits the use of such hybrid states for practical applications. Here we report, on a simple generic experimental scheme to generate hybrid entangled states in polarization and OAM through direct transfer of classical non-separable states of the pump beam in parametric down conversion process. As a proof of principle, using local non-separable pump states of OAM mode l = 3, we have produced quantum hybrid entangled states with entanglement witness parameter of ~1.25 ± 0.03 violating by 8 standard deviation.

Tunable vector-vortex beam optical parametric oscillator

“…Both QWPs (QWP1 and QWP2) had optic axis rotated by +45° with respect to horizontal axis. We analyzed the out-coupled signal from mirror, M3, using a detection unit comprising the combination of QWP, λ /2 plate, and a PBS 6 . We projected the signal vector-vortex beam of OAM mode, l = 1, in different polarization states, horizontal (H), vertical (V), diagonal (D), anti-diagonal (A), right circular (R), and left circular (L), on the Poincaré sphere, by adjusting the optic axis of the QWP and λ /2 plate.…”

“…Due to the vector nature (polarization), together with the vortex intensity distribution, such special class of beams are known as vector-vortex beams. Vector-vortex beams, having both phase and polarization singularities, are of great interest for a variety of applications, for example, in material processing 4 , optical trapping 5 , photon entanglement 6 , and microscopy 7 . The vector-vortices are described by points on the higher-order Poincaré sphere (HOP) 8 , representing the total angular momentum of light.…”

Vectorial light-matter interaction -- exploring spatially structured complex light fields

“…Alternatively, rather than introducing vector properties to already entangled photons, the procedure can be reversed: the possibility of directly converting a vector beam via SPDC into hybrid entangled photon pairs has been suggested 183 and realised. 184 The nonlinear properties of the χ 2 crystal can be considered for the independent polarization components of the vectorial pump beam, but specific care must be taken with phase-matching. The process of phase conjugation of vector beams was investigated theoretically for stimulated parametric downconversion.…”

Torsion-induced optical �triaxiality� of LiNbO3 crystals

“…This is due to unusual physical behaviour of OVs and promises of their applications in such novel branches of technology as quantum encoding [2], quantum teleportation [3] and microparticles manipulation [4]. Most of these applications are associated with quantum properties of the OVs, because they bear nonzero orbital angular momentum l (with l being integer) that represents their charge [5].…”