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A Photonic System for Generating Unconditional Polarization-Entangled Photons Based on Multiple Quantum Interference
Published on: September 5, 2019
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Nonlocal realism tests and quantum state tomography in Sagnac-based type-II polarization-entanglement SPDC-source.
Ali Motazedifard1,2,3, S A Madani1,2, J J Dashkasan1
1Quantum Optics Group, Iranian Center for Quantum Technologies (ICQTs), Tehran, Iran.
Heliyon
|July 14, 2021
Summary
Researchers created a bright, stable, polarization-entangled quantum state using spontaneous parametric down-conversion in a Sagnac interferometer. This state strongly violates Bell inequalities, confirming quantum mechanics over classical theories for quantum communication applications.
Area of Science:
- Quantum Optics
- Quantum Information Science
- Experimental Physics
Background:
- Entangled quantum states are crucial for quantum information processing.
- Previous methods faced challenges in brightness, stability, and fidelity.
- Spontaneous parametric down-conversion (SPDC) is a key source for entangled photons.
Purpose of the Study:
- To experimentally generate a robust, ultrabright, and phase-stable polarization-entangled state.
- To achieve high fidelity close to a maximally entangled Bell state.
- To demonstrate strong violations of Bell inequalities, confirming quantum non-locality.
Main Methods:
- Utilized type-II SPDC in a periodically-poled KTiOPO4 (PPKTP) crystal within a Sagnac interferometer (SI).
- Performed Bell inequality measurements (CHSH, Freedman's test) and visibility tests.
- Employed quantum state tomography with maximum-likelihood-technique (MLT) for density operator reconstruction.
Main Results:
- Generated a polarization-entangled state with 98% fidelity.
- Achieved high brightness ( and ) and phase stability.
- Demonstrated significant Bell violation () and Freedman test violation (), exceeding classical predictions.
Conclusions:
- The Sagnac configuration enables a high-rate, robust entangled photon source.
- The results confirm the non-classical nature of the entangled state, violating local realism.
- The source is highly applicable for quantum communication, sensing, metrology, and quantum key distribution (QKD).
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