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

TL;DR

This paper presents a simple method to generate hybrid entangled photon states by directly transferring a classical non-separable pump beam state into quantum entanglement, avoiding complex mode conversion procedures.

Contribution

The authors introduce a novel, straightforward experimental scheme for creating hybrid entangled states via direct transfer from classical non-separable states, enhancing practicality for quantum applications.

Findings

Successfully generated hybrid entangled states with entanglement witness W-1.25

Demonstrated violation of classical bounds by 8 standard deviations

Scheme allows flexible entanglement between photons with different quantum numbers

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 state 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 state for practical applications. Here we report, on a simple experimental scheme to generate hybrid entangled state in polarization and OAM through direct transfer of classical non-separable state of the pump beam in parametric down conversion process. As a proof of principle, using local non-separable pump state of OAM mode l=3, we have produced quantum hybrid entangled state with entanglement witness parameter of W-1.25 violating by 8 standard deviation. The generic scheme can be used to produce hybrid entangled state between two photons differing by any quantum number through proper choice of non-separable state of the pump beam.