Advanced photonic quantum technology relies on multi-photon interference which requires bright sources of high-purity single photons. Here, we implement a novel domain-engineering technique for tailoring the nonlinearity of a parametric down-conversion crystal. We create pairs of independentlyheralded telecom-wavelength photons and achieve high heralding, brightness and spectral purities without filtering.The ability of generating and manipulating single quanta of light enables the possibility of exploring new quantumenhanced technologies. Thanks to their robust coherence and the possibility of travelling over long distances with low losses, single photons are the ideal carriers of quantum information in large scale quantum networks [1-3]. Recent works have shown how photonic platforms are suitable not only for communication purposes, but also play a role in other areas of quantum information, such as quantum computing [4][5][6] and simulation [7,8]. In particular, scalable/fault-tolerant linear optical quantum computing (LOQC) appears to be a promising platform for quantum computing [9,10]. However, LOQC requires photons with near-unity purities and heralding efficiencies [11,12], as each percentage point in unsuccessful gate operation or photon loss comes at a significant overhead cost in the required number of photon sources, detectors and circuit complexity [13,14].

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We present an efficient experimental procedure that certifies nonvanishing quantum capacities for qubit noisy channels. Our method is based on the use of a fixed bipartite entangled state, where the system qubit is sent to the channel input. A particular set of local measurements is performed at the channel output and the ancilla qubit mode, obtaining lower bounds to the quantum capacities for any unknown channel with no need of quantum process tomography. The entangled qubits have a Bell state configuration and are encoded in photon polarization. The lower bounds are found by estimating the Shannon and von Neumann entropies at the output using an optimized basis, whose statistics is obtained by measuring only the three observables σ_{x}⊗σ_{x}, σ_{y}⊗σ_{y}, and σ_{z}⊗σ_{z}.