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Hybrid quantum networks for spin coherent technologies

Final Report Summary - HYSCORE (Hybrid quantum networks for spin coherent technologies)

Entanglement – the property that particles can share a single quantum state - is arguably the most counterintuitive yet potentially most powerful element of quantum physics. Future quantum networks may harness the unique features of entanglement in a range of exciting applications, such as quantum computation and simulation, secure communication, enhanced metrology for astronomy and time-keeping as well as fundamental tests of nature. To fulfill these promises, a strong worldwide effort is ongoing to gain precise control over multi-particle nodes and to wire them up using quantum-photonic channels.
In the HYSCORE project, a research team led by PI Ronald Hanson has laid the foundation for such a future network based on single electrons spins associated with NV centers in diamond. In particular, the project achieved two major breakthroughs.

First, they were able to perform closed-loop control of individual electron and nuclear spins. Whereas all previous experiments had used open-loop control, the researchers implemented a fast feedback cycle based on quantum measurements and rapid signal processing. This way, they could steer the quantum states in real-time based on measurement outcomes. They applied these new techniques to implement quantum error correction on a continuously encoded quantum bit, showing improvements in the preservation of certain quantum states.

Second, the project demonstrated the first entanglement between remote solid-state chips, through a photon-mediated entangling scheme between two NV electron spins that were 3 meters apart. Then they used this technique to show quantum teleportation of a quantum state over the same distance. By increasing the distance to 1.3km the team was able to perform the first test of Bell’s inequalities with all the loopholes closed. The latter two experiment gained worldwide attention. In the final stage of the project, the control of nuclear spins was combined with the remote entanglement of electrons for entanglement distillation: out of two weakly entangled pairs of quantum bits one strongly entangled pair was distilled using quantum control and measurements.
The HYSCORE project has pushed the NV center platform to the frontier of quantum information processing, and in particular made it a leading candidate for implementing first rudimentary multi-node quantum networks.