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IEEE International Conference on Quantum Computing and Engineering (QCE)

Biphoton Quantum State Tomography and Spin-orbit Conversion in C+L Telecom Bands

Mostafa Youssef, Neelan Gounden, Pedro Ornelas, Isaac M. Nape, Andrew Forbes, Bora Ung

Published Sep 15, 2024• 0 citations
Publisher

Abstract

High-dimensional quantum states offer the promise of enhancing information capacity in quantum communications. Towards that goal, we here characterize a fiber-based system with the generation and transmission of biphotons in the telecom C+L bands and capable of converting photons with low-dimensional spin subspace to a high-dimensional orbital angular momentum (OAM) subspace (from -5 to +5 topological charge). We experimentally confirm that Bell's inequality is violated with a CHSH value of 2.43. The reconstructed density matrix through polarization quantum state tomography (QST) indicates a fidelity of 92 %, a purity of 86 % and concurrence of 84 % are achieved. The spin (polarization) to OAM conversion through spatial light modulator (SLM) is shown to yield a conversion efficiency of 41.5 %. This work is a step towards achieving multidimensional entanglement and high-dimensional quantum key distribution at standard fiber telecom wavelengths.

DOI
10.1109/qce60285.2024.10409

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Entanglement distribution between distant parties is one of the most important and challenging tasks in quantum communication. Distribution of photonic entangled states using optical fiber links is a fundamental building block towards quantum networks. Among the different degrees of freedom, orbital angular momentum (OAM) is one of the most promising due to its natural capability to encode high dimensional quantum states. In this article, we experimentally demonstrate fiber distribution of hybrid polarization-vector vortex entangled photon pairs. To this end, we exploit a recently developed air-core fiber which supports OAM modes. High fidelity distribution of the entangled states is demonstrated by performing quantum state tomography in the polarization-OAM Hilbert space after fiber propagation, and by violations of Bell inequalities and multipartite entanglement tests. The present results open new scenarios for quantum applications where correlated complex states can be transmitted by exploiting the vectorial nature of light.
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