Periodic Reporting for period 4 - QuantumNet (A Scalable Quantum Network based on Individual Erbium Ions)
Período documentado: 2022-09-01 hasta 2024-02-29
A future quantum network will consist of quantum processors that are connected by quantum channels, just like conventional computers are wired up to form the Internet. In contrast to classical devices, however, the entanglement and non-local correlations available in a quantum-controlled system facilitate novel fundamental tests of quantum theory and numerous applications. In particular, quantum networks can fundamentally enhance computational power, ensure provably-secure communication, and simulate complex quantum systems to aid the search for new materials and drugs.
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.
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.
The project has fully achieved two out of the three originally proposed objectives, and made decisive steps towards achieving the third. This will be explained in detail in the following:
(I) The first objective of the proposal was the implementation of a quantum spin-photon interface at a telecommunication wavelength. To this end, we have integrated a thin membrane of yttrium orthosilicate into a cryogenic Fabry-Perot resonator. We could demonstrate that our approach preserves the coherence of the dopants (Merkel et al. Phys. Rev. X 2020), and is compatible with microwave control (Cova Fariña et al., Phys. Rev. Applied 2021) and dynamical decoupling to further extend the coherence time (Merkel et al. Phys. Rev. Lett. 2021). In addition, we pioneered the use of silicon as an alternative host material (Weiss et al. Optica 2021) that can give access to higher rates and improved coherence (Gritsch et al. Phys. Rev. X. 2022) and is compatible with commercial semiconductor manufacturing (Rinner et al. Nanophotonics 2023). The process of emitter integration into silicon has been patented (WO2022258204A1) and first steps towards commercialization are currently taken by the project members.
(II) The second objective was the multiplexing of many quantum bits in one device via frequency-selective addressing. We could demonstrate this both in YSO crystals (Ulanowski et al. Sci. Adv. 2022) and in silicon (Gritsch et al. Optica. 2023). Recent results have increased the number of frequency-multiplexed and Purcell enhanced qubits to the current world-record value of 350 (Ulanowski et al. Advanced Optical Materials 2024).
(III) The third objective of the proposal was the implementation of remote entanglement swapping. This goal has not been achieved yet because of unexpectedly large spectral diffusion of the emitters. However, by now we have identified mechanisms how this can be overcome, and we have demonstrated several key steps towards this end: 1) The world’s first optical initialization, readout and control of spins in silicon (Gritsch et al, in preparation), and 2), the first demonstration of these techniques with single nuclear spins (Ulanowski et al, in preparation). These advancements bring achieving the final goal of the objective within reach.
Taken together, our progress in the new platform makes the implementation of large-scale quantum networks and repeaters based on erbium dopants a realistic perspective for the coming years.
To disseminate the results, the group has written review articles for a broader audience in quantum science (Reiserer, Rev. Mod. Phys. 2022, Gonzalez-Tudela et al. Nat. Rev. Phys. 2023), as well as popular research articles for the general public (Reiserer, Physik in unserer Zeit, 2022). In addition, press releases by the institutes and videos distributed via the social media have disseminated the project ideas and results to a broad audience.
(I) The first objective of the proposal was the implementation of a quantum spin-photon interface at a telecommunication wavelength. To this end, we have integrated a thin membrane of yttrium orthosilicate into a cryogenic Fabry-Perot resonator. We could demonstrate that our approach preserves the coherence of the dopants (Merkel et al. Phys. Rev. X 2020), and is compatible with microwave control (Cova Fariña et al., Phys. Rev. Applied 2021) and dynamical decoupling to further extend the coherence time (Merkel et al. Phys. Rev. Lett. 2021). In addition, we pioneered the use of silicon as an alternative host material (Weiss et al. Optica 2021) that can give access to higher rates and improved coherence (Gritsch et al. Phys. Rev. X. 2022) and is compatible with commercial semiconductor manufacturing (Rinner et al. Nanophotonics 2023). The process of emitter integration into silicon has been patented (WO2022258204A1) and first steps towards commercialization are currently taken by the project members.
(II) The second objective was the multiplexing of many quantum bits in one device via frequency-selective addressing. We could demonstrate this both in YSO crystals (Ulanowski et al. Sci. Adv. 2022) and in silicon (Gritsch et al. Optica. 2023). Recent results have increased the number of frequency-multiplexed and Purcell enhanced qubits to the current world-record value of 350 (Ulanowski et al. Advanced Optical Materials 2024).
(III) The third objective of the proposal was the implementation of remote entanglement swapping. This goal has not been achieved yet because of unexpectedly large spectral diffusion of the emitters. However, by now we have identified mechanisms how this can be overcome, and we have demonstrated several key steps towards this end: 1) The world’s first optical initialization, readout and control of spins in silicon (Gritsch et al, in preparation), and 2), the first demonstration of these techniques with single nuclear spins (Ulanowski et al, in preparation). These advancements bring achieving the final goal of the objective within reach.
Taken together, our progress in the new platform makes the implementation of large-scale quantum networks and repeaters based on erbium dopants a realistic perspective for the coming years.
To disseminate the results, the group has written review articles for a broader audience in quantum science (Reiserer, Rev. Mod. Phys. 2022, Gonzalez-Tudela et al. Nat. Rev. Phys. 2023), as well as popular research articles for the general public (Reiserer, Physik in unserer Zeit, 2022). In addition, press releases by the institutes and videos distributed via the social media have disseminated the project ideas and results to a broad audience.
We have shown that the emission of erbium dopants can be strongly enhanced by a resonator while at the same time preserving their excellent optical coherence properties. Compared to competing experiments with cryogenic Fabry-Perot resonators, we have increased the stability and the finesse approximately hundredfold. Compared to state-of-the-art systems with rare-earth dopants in nanophotonic resonators, we observe an increase of the optical coherence by two to three orders of magnitude.
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 and spin-control in this novel materials platform, opening unique perspectives for the realization of integrated quantum networks based on established fabrication processes of the semiconductor industry.
Furthermore, we have demonstrated the control of single spins, and frequency-domain multiplexing of many spins in one device.
Finally, we have taken decisive steps towards the generation of spin-photon and spin-spin entanglement. Each of these results has significantly pushed the state of the art towards the realization of global quantum networks via quantum repeaters.
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 and spin-control in this novel materials platform, opening unique perspectives for the realization of integrated quantum networks based on established fabrication processes of the semiconductor industry.
Furthermore, we have demonstrated the control of single spins, and frequency-domain multiplexing of many spins in one device.
Finally, we have taken decisive steps towards the generation of spin-photon and spin-spin entanglement. Each of these results has significantly pushed the state of the art towards the realization of global quantum networks via quantum repeaters.