Persistent atomic frequency comb based on Zeeman sub-levels of an erbium-doped crystal waveguide
Long-lived sub-levels of the electronic ground-state manifold of rare-earth ions in crystals can be used as atomic population reservoirs for photon echo-based quantum memories. We measure the dynamics of the Zeeman sub-levels of erbium ions that are doped into a lithium niobate waveguide, finding population lifetimes at cryogenic temperatures down to 0.7 K as long as seconds. Then, using these levels, we prepare and characterize atomic frequency combs (AFCs), which can serve as a memory for quantum light at 1532 nm wavelength. The results allow predicting a 0.1% memory efficiency, limited mainly by unwanted background absorption that we believe to be caused by excitation-induced erbium spin flips and frequency shifting due to two-level systems or non-equilibrium phonons. Hence, while it should be possible to create an AFC-based quantum memory in Er³⁺:Ti⁴⁺:LiNbO₃, improved crystal growth together with optimized AFC preparation will be required to make it suitable for applications in quantum communication.
© 2020 Optical Society of America. Received 18 July 2019; revised 2 November 2019; accepted 9 December 2019; posted 11 December 2019 (Doc. ID 373100); published 20 January 2020. The authors thank Wolfgang Sohler, Mathew George, and Raimund Ricken for providing the waveguide, and Jacob H. Davidson for help with aligning the waveguide and Gustavo Amaral and Erhan Saglamyurek for useful discussions. N.S. acknowledges funding from the AQT's Intelligent Quantum Networks and Technologies (INQNET) research program, and W.T. support as a Senior Fellow of the Canadian Institute for Advanced Research (CIFAR). Funding: Alberta Innovates - Technology Futures; Natural Sciences and Engineering Research Council of Canada; Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO); Canadian Institute for Advanced Research; AQT's Intelligent Quantum Networks and Technologies (INQNET); Alberta Major Innovation Fund.