Entanglement distribution over quantum networks has the promise of realizing fundamentally new technologies. Entanglement between separated quantum processing nodes has been achieved on several experimental platforms in the past decade. To move toward metropolitan-scale quantum network test beds, the creation and transmission of indistinguishable single photons over existing telecom infrastructure is key. Here, we report the interference of photons emitted by remote spectrally detuned NV-center-based network nodes, using quantum frequency conversion to the telecom L band. We find a visibility of 0.79±0.03 and an indistinguishability between converted NV photons around 0.9 over the full range of the emission duration, confirming the removal of the spectral information present. Our approach implements fully separated and independent control over the nodes, time multiplexing of control and quantum signals, and active feedback to stabilize the output frequency. Our results demonstrate a working principle that can be readily employed on other platforms and shows a clear path toward generating metropolitan-scale solid-state entanglement over deployed telecom fibers.@en

We show the latest progress towards establishing a solid-state, metropolitan quantum link, consisting of two remote Nitrogen Vacancy (NV)-centers and a central measurement station. The entanglement is generated by converting single emitted photons to the same frequency in the telecom L-band, guiding them to a central beamsplitter, where a joint Bell-state measurement projects the NV-centre spins in an entangled state.@en

Quantum technology allows for unparalleled levels of data and software protection. Probabilistic one-time programs harness these capabilities for quantum-assisted classical computations by encoding classical software in small quantum states resulting in computer programs that can be used only once. Such self-destructing one-time programs facilitate a variety of applications reaching from software distribution to one-time delegation of signature authority. Whereas previous experiments demonstrated the feasibility of such schemes, the practical applications were limited. Here we present an improved protocol for one-time programs that resolves major drawbacks of previous schemes, by employing entangled qubit pairs. This results in four orders of magnitude higher count rates and the ability to execute a program long after the quantum information exchange has taken place. We implement a one-time delegation of signature authority over an underground fiber link between university buildings in downtown Vienna, emphasizing the compatibility of our scheme with prepare-and-measure quantum internet networks.@en

We demonstrate interference of photons emitted by remote, spectrally distinct NV-centers. Quantum frequency conversion at the nodes brings the photons to the same wavelength in the telecom L-band, compatible with entanglement generation at metropolitan scale.@en

We demonstrate interference of photons emitted by remote, spectrally distinct NV-centers. Quantum frequency conversion at the nodes brings the photons to the same wavelength in the telecom L-band, compatible with entanglement generation at metropolitan scale.@en