Abstract
Quantum emitters generating individual entangled photon pairs (IEPP) have significant fundamental advantages over schemes that suffer from multiple photon emission, or schemes that require post-selection techniques or the use of photon-number discriminating detectors. Quantum dots embedded within nanowires (QD-NWs) represent one of the most promising candidate for quantum emitters that provide a high collection efficiency of photons. However, a quantum emitter that generates IEPP in the telecom band is still an issue demanding a prompt solution. Here, we demonstrate in principle that IEPPs in the telecom band can be created by combining a single QD-NW and a nonlinear crystal waveguide. The QD-NW system serves as the single photon source, and the emitted visible single photons are split into IEPPs at approximately 1.55 μm through the process of spontaneous parametric down conversion (SPDC) in a periodically poled lithium niobate (PPLN) waveguide. The compatibility of the QD-PPLN interface is the determinant factor in constructing this novel hybrid-quantum-emitter (HQE). Benefiting from the desirable optical properties of QD-NWs and the extremely high nonlinear conversion efficiency of PPLN waveguides, we successfully generate IEPPs in the telecom band with the polarization degree of freedom. The entanglement of the generated photon pairs is confirmed by the entanglement witness. Our experiment paves the way to producing HQEs inheriting the advantages of multiple systems.
Highlights
As reliable quantum emitters, single semiconductor QDs have been shown to be excellent building blocks in the fields of quantum computation[1], quantum cryptography[2] and quantum optics[3]
A newly designed Quantum dots embedded within nanowires (QD-NWs) is used as the single photon emitter
To identify the most suitable QD-NW to achieve the highest compatibility of the periodically poled lithium niobate (PPLN) waveguide, we narrow the search range within 10 nm around 775 nm
Summary
Single semiconductor QDs have been shown to be excellent building blocks in the fields of quantum computation[1], quantum cryptography[2] and quantum optics[3]. Single QDs’ desirable optical properties substantially meet the requirements of a single-photon emitter, including high-fidelity anti-bunching, narrow emission lines and high brightness. They can potentially be integrated into monolithic structures, such as optical microcavities[4,5] and electrical charge-tuning devices[6]. Developing a quantum emitter that generates IEPPs remains a technological challenge Both polarization[15] and time-bin entangled photon pairs[16] were realized in a quantum dot system through a cascade radiation process. The introduction of optical waveguides etched in a PPLN crystal has further increased the conversion efficiencies to 10−6 25, enabling single-photon-level SPDC. There is no physical limit to prevent the conversion efficiency from approaching the value of 1
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