On-chip quantum memories based on erbium dopants in silicon waveguides
Final Report Abstract
The implementation of large-scale quantum networks is hindered by photon loss that is unavoidable in photonic channels. This obstacle can be overcome by quantum repeater protocols. Their implementation requires quantum memories that fulfil stringent requirements: They should offer a long coherence time (on the order of one second) and facilitate the efficient storage and on-demand retrieval of qubits with high efficiency and fidelity. Furthermore, they may act as a source of single photons and provide a simple strategy for multiplexing. In spite of numerous efforts in different physical systems, however, the implementation of such quantum memories is an outstanding challenge. In the present project, a new hardware platform has been investigated towards this goal. To this end, erbium dopants have been integrated into nanophotonic structures. By confining the light field of impinging photons into waveguides and resonators, a quantum interface between impinging photons in the telecommunications C-band and ensembles of erbium emitters has been implemented. Its narrow homogeneous linewidth – below 10 kHz – entails a better optical coherence than most other nanophotonic quantum memories. The spin state of the dopants has been initialized by optical pumping, leading to spectral hole burning with a measured hole lifetime exceeding seconds at temperatures below 4 K. Because of the moderate integration yield, achieving a high memory efficiency requires enhancing the optical density of states. To this end, photonic crystal structures have been investigated, achieving an enhancement factor of more than 100. This allows for the addressing and control of individual erbium dopants using frequency-multiplexed optical excitation pulses. Thus, in small nanophotonic resonators, a Purcell-enhanced quantum memory that can efficiently emit single photons and offers a coherence of 0.05 ms has been demonstrated. The coherence can be improved in the future by dynamical decoupling, possibly up to the lifetime limit of several seconds. Finally, it has been shown that corresponding devices can be fabricated by a commercial nanophotonics foundry. Taken together, these advantages pave the way for the use of the new hardware platform in quantum networks and quantum repeaters.
Publications
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"Photonic Element for a Quantum Information Processing Device and Method for Producing Such," U.S. patent WO2022258204A1 (December 15, 2022).
A. Reiserer, A. Gritsch & L. Weiss
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Narrow Optical Transitions in Erbium-Implanted Silicon Waveguides. Physical Review X, 12(4).
Gritsch, Andreas; Weiss, Lorenz; Früh, Johannes; Rinner, Stephan & Reiserer, Andreas
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Erbium emitters in commercially fabricated nanophotonic silicon waveguides. Nanophotonics, 12(17), 3455-3462.
Rinner, Stephan; Burger, Florian; Gritsch, Andreas; Schmitt, Jonas & Reiserer, Andreas
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Purcell enhancement of single-photon emitters in silicon. Optica, 10(6), 783.
Gritsch, Andreas; Ulanowski, Alexander & Reiserer, Andreas
