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.
Highlights
Entanglement, the quintessential strong non-classical correlations in joint measurement of at least two separate quantum systems, plays a critical role in many important applications in quantum information processing, including quantum communication[1], quantum computation[2], quantum cryptography[3], dense coding[4] and teleportation[5]
With the first demonstration of entanglement with polarization DoF10, 11, recent advancement in quantum optics have provided intrinsic entanglement (entanglement in variety of DoFs such as orbital angular momentum (OAM)[12], energy time[13], time bin[14], and many more)[15], hyperentanglement[16] and hybrid entanglement. While these entangled states have various applications, the hybrid entangled states encoded with polarization and OAM, in particular, allow the generation of qubit-qudit entangled states[17] for quantum information, macroscopic entanglement with very high quanta of OAM18, important for quantum information science, and supersensitive measurement of angular displacement in remote sensing[19]
Hybrid entangled states encoded with polarization and OAM are generated through the imprinting of chosen amount of OAM to a high-fidelity polarization entangled state using mode converters, such as, spatial light modulator (SLM)[20] and q-plate[21], in complicated experimental schemes
Summary
Entanglement, the quintessential strong non-classical correlations in joint measurement of at least two separate quantum systems, plays a critical role in many important applications in quantum information processing, including quantum communication[1], quantum computation[2], quantum cryptography[3], dense coding[4] and teleportation[5]. With the first demonstration of entanglement with polarization DoF10, 11, recent advancement in quantum optics have provided intrinsic entanglement (entanglement in variety of DoFs such as orbital angular momentum (OAM)[12], energy time[13], time bin[14], and many more)[15], hyperentanglement[16] (entanglement in every DoFs) and hybrid entanglement (entanglement between different DoFs of a pair of particles) While these entangled states have various applications, the hybrid entangled states encoded with polarization and OAM, in particular, allow the generation of qubit-qudit entangled states[17] for quantum information, macroscopic entanglement with very high quanta of OAM18, important for quantum information science, and supersensitive measurement of angular displacement in remote sensing[19]. In addition to the photon losses, the alignment of SLM especially at significantly lower number of photons generated in SPDC process is very much complicated than using the same device for the pump beam To circumvent such problem, as such, it is imperative to device alternative techniques to produce hybrid entangled states in simple experimental scheme. The concern of rapidly decreasing efficiency of the down conversion process for the direct generation of entanglement at higher OAM, can be overcome by using the OAM independent beam size of the non-separable states using the scheme mentioned in previous reports[23, 31]
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