Quantum-optical technologies are transforming communication and metrology by enabling security and sensitivity beyond classical limits. Currently, these technologies are available at visible, near-infrared (NIR) and telecom wavelengths but are strongly underdeveloped at longer wavelengths. There is a growing demand for quantum sources operating in the 2 μm region for various applications. For example, such sources can enable daylight satellite-to-ground based quantum communications by taking advantage of an atmospheric transparency window with reduced solar blackbody radiation compared to telecom wavelengths [1,2,3]. Moreover, squeezed 2 μm sources are expected to have an impact on quantum metrology. For example, in gravitational wave detectors (eg. LIGO), such long wavelengths could reduce the quantum noise and scattering loss from crystalline silicon test masses . Here, we report the generation and characterisation of a photon pair source at 2.080 μm with coincidence-to-accidental ratio (CAR) exceeding 10.
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