Periodic Reporting for period 3 - QuantumNet (A Scalable Quantum Network based on Individual Erbium Ions)
Periodo di rendicontazione: 2021-03-01 al 2022-08-31
While pioneering experiments have demonstrated the entanglement of two quantum nodes separated by up to 1.3 km, accessing the full potential of quantum networks requires scaling of these prototypes to more nodes and larger distances. This requires the development of a new technology that overcomes the bottlenecks of existing physical systems. To this end, we harness the exceptional properties of individual Erbium ions embedded in silicon and silicate crystals. The key steps towards increasing the size of quantum networks based on this platform are, first, the implementation of efficient quantum network nodes at a telecommunication wavelength, second, increasing the number of quantum bits in such node via frequency-selective addressing, and, third, the implementation of efficient protocols to generate entanglement between the nodes. Based on these advances, we plan to demonstrate a prototype quantum repeater, a milestone advancement towards global quantum networks.
In the second setup, we have started to investigate an alternative host material that avoids the mentioned challenges, crystalline silicon. In stark contrast to previous work, we have shown that Erbium can be integrated at well-defined lattice sites using an optimized implantation and annealing procedure. This has allowed us to achieve a three-orders of magnitude improved inhomogeneous distribution, which should be sufficient for the control of individual ions. We have summarized these findings in a publication, arXiv:2005.01775 (with referees).
Finally, we have investigated spin-spin interactions within rare-earth doped crystals. In contrast to the expectation of the community, we have demonstrated that these interactions cannot be efficiently decoupled my microwave control, which poses a severe limitation to quantum memory experiments with dense ensembles. We have summarized these results in
arXiv:2005.08822 (with referees). Our findings thus highlight the importance of our cavity-enhanced single-ion approach that can overcome the mentioned limitation.
In summary, we have successfully completed most of the targeted work packages (ensemble spectroscopy, laser stabilization, spin readout and ground state control, spin-spin interactions within a node, construction of setup B, sample and setup optimization).
In addition, we have demonstrated that ion implantation allows one to integrate erbium into silicon at well-defined lattice sites, in striking contrast to the findings of numerous previous works. Recently, we have succeeded in single-ion spectroscopy in this novel materials platform, opening unique perstpectives for the realization of integrated quantum networks based on established fabrication processes of the semiconductor industry.
We expect that in spite of additional delay caused by the COVID-crisis, we can still complete most of the work packages of the original proposal. This includes in particular the control of single spins, frequency-domain multiplexing of many spins in one device, and the generation of spin-photon and spin-spin entanglement. Albeit some of these topics have by now been addressed in competing physical platforms, we expect that our results in each of them will further push the state of the art towards the realization of global quantum networks via quantum repeaters.