The realization of a highly connected network of qubit registers is a central challenge for quantum information processing and long-distance quantum communication. Diamond spins associated with NV centers are promising building blocks for such a network as they combine a coherent optical interface (similar to that of trapped atomic qubits)  with a local register of robust and well-controlled nuclear spin qubits . We can now exploit these features simultaneously to achieve new functionalities such as unconditional remote quantum teleportation .
Here we present our latest progress towards scalable quantum networks, including the first loophole-free violation of Bell’s inequalities . Our Bell test is free of any experimental loopholes and thus directly tests the principles underlying the nature of reality. We create and exploit high-fidelity entanglement between diamond electron spins separated by more than 1 km, and combine this with efficient state detection to obtain a Bell violation.
I will discuss how the techniques developed in these experiments may enable the realization of a network of quantum bit registers for quantum computation and communication. In the long run, such networks may lead to a quantum Internet secured through device-independent protocols – reaching the ultimate physical limits of privacy .
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