Entangled photon-pairs are crucial for applications like quantum key distribution, sensing and imaging. For prospective use in real world devices, the challenge for Entangled Photon-Pair Sources (EPS) is to simultaneously meet high requirements regarding state fidelity, tunability etc. while maintaining a small footprint and high robustness. In this work, we develop an EPS that meets these demands. Using a sub-micron thick Transition Metal Dichalcogenide (TMD) crystal, we show tunable generation of polarization entangled Bell states via Spontaneous Parametric Down-Conversion (SPDC). To the best of our knowledge, this is the first realization of SPDC in a TMD. In particular, we employ the TMD 3R-phase molybdenum disulfide (3R-MoS2), which due to its crystal symmetry intrinsically creates entanglement without needing external optical components. We experimentally demonstrate tuning between different maximally entangled states with constant generation efficiency and show pathways towards highly efficient and tunable TMD-based EPS using quasi-phasematching or cavity integration.
Ultrathin metasurfaces have shown the capability to influence all aspects of light propagation. This has made them promising options for replacing conventional bulky imaging optics while adding advantageous optical properties or functionalities. We demonstrate that such metasurfaces can also be applied for single-lens three-dimensional (3-D) imaging based on a specifically engineered point-spread function (PSF). Using Huygens’ metasurfaces with high transmission, we design and realize a phase mask that implements a rotating PSF for 3-D imaging. We experimentally characterize the properties of the realized double-helix PSF, finding that it can uniquely encode object distances within a wide range. Furthermore, we experimentally demonstrate wide-field depth retrieval within a 3-D scene, showing the suitability of metasurfaces to realize optics for 3-D imaging, using just a single camera and lens system.
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