Remote Preparation of Single-Photon "Hybrid" Entangled and Vector-Polarization States (1009.5412v1)

Abstract: Quantum teleportation faces increasingly demanding requirements for transmitting large or even entangled systems. However, knowledge of the state to be transmitted eases its reconstruction, resulting in a protocol known as remote state preparation. A number of experimental demonstrations to date have been restricted to single-qubit systems. We report the remote preparation of two-qubit "hybrid" entangled states, including a family of vector-polarization beams. Our single-photon states are encoded in the photon spin and orbital angular momentum. We reconstruct the states by spin-orbit state tomography and transverse polarization tomography. The high fidelities achieved for the vector-polarization states opens the door to optimal coupling of down-converted photons to other physical systems, such as an atom, as required for scalable quantum networks, or plasmons in photonic nanostructures.

• The paper introduces a novel protocol that remotely prepares high-fidelity single-photon hybrid entangled and vector-polarization states.
• The paper employs spin and orbital angular momentum to achieve approximately 95% fidelity while controlling decoherence.
• The paper eliminates the need for complete Bell-state analysis, paving the way for more efficient and scalable quantum networks.

Remote Preparation of Single-Photon Hybrid Entangled and Vector-Polarization States

This paper presents a significant advancement in the domain of quantum state manipulation, focusing on the remote preparation of hybrid entangled states and vector-polarization states using single photons. The authors, Barreiro, Wei, and Kwiat, introduce a protocol that significantly expands the operational parameters of remote state preparation (RSP). Unlike traditional quantum teleportation which requires comprehensive state analysis, RSP leverages partial knowledge about the quantum state to optimize resource utilization. The paper extends the RSP paradigm beyond single-qubit frameworks into the more complex territory of two-qubit hybrid entangled states, which are essential for developing scalable quantum networks.

The research demonstrates the remote preparation of entangled states involving both the spin and orbital angular momentum (OAM) of photons, achieving reliable state reconstruction via sophisticated tomography processes. This enables the conversion of a single-photon state into a spatially separated entangled state, a process facilitated by "hyperentanglement" in multiple degrees of freedom. The use of vector-polarization states, which offer nonuniform transverse polarization, is also discussed. These states exhibit high fidelity and are inherently suitable for potential applications in quantum metrology, optimal plasmon production, and atom coupling.

Several notable results are highlighted in the paper:

• The single-photon entangled states were prepared with high fidelity, achieving measurements around 95%. This surpasses previous attempts and reflects the robustness of the hybrid entanglement method employed, especially in comparison to traditional entanglement swapping methods.
• The experiment achieves highly controlled decoherence effects to simulate the preparation of mixed quantum states of remote systems, an essential feature for realistic quantum communication scenarios.

The broader implications of this research lie in its set of protocols that are adaptable for a wider range of quantum systems, providing unique approaches to remotely manipulating multiqubit states. The development utilizes entanglement swapping to enhance remote preparation efficiency, eliminating the need for Bell-state analysis—a known limitation when using linear optics alone.

Future research can leverage these findings to develop more complex quantum networks, wherein high-dimensional entangled states with modified protocols could support not only advanced quantum communication tasks but also introduce efficiencies in quantum energy transfer.

The results contribute significantly to theoretical and practical realms, offering a path forward in reducing the resource constraints of quantum state communication, fostering the development of efficient quantum networking, and enabling high-fidelity quantum state preparation with fewer classical resources. Further investigation may explore incorporating additional degrees of freedom to enrich the spectrum of applicable states and explore diverse applications in emerging quantum technologies.