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    • USTC Fabricates Integrable Solid-State Quantum Memories with High Fidelity

    • [2020-03-11]
    • Mapping quantum information between light and matter, optical quantum memories are crucial devices in large-scale quantum networks. Based on bulk rare-earth-ion-doped crystals, quantum memories with high fidelity, multi-mode capacity and long storage time can be demonstrated. 151Eu3+-doped yttrium silicate (151Eu3+ : Y2SiO5) crystal is an attractive candidate for this. However, there have been no demonstrations of integrated memories in this material. Also, storage fidelity of the memory after fabrication using femtosecond-laser micromachining (FLM) has never been quantitatively characterized before.

      The research team led by academician GUO Guangcan, professor LI Chuanfeng and ZHOU Zongquan from University of Science and Technology (USTC) of Chinese Academy of Sciences (CAS) reported the fabrication of type II waveguides in a 151Eu3+ : Y2SiO5 crystal using FLM. The research team optimized fabrication parameters to ensure that the waveguides were compatible with single-mode fibers (SMFs). Based on the spin-wave atomic frequency comb (AFC) scheme and the revival of silenced echo (ROSE) scheme, on-demand light storage was demonstrated in the waveguide section. The team then characterized storage fidelity of the memory by performing a series of interference experiments. Interference visibility of the readout pulses are high for both schemes, demonstrating the reliability of the integrated optical memory.

      This work was published in Optica on Feb 20th and commented by the reviewer as “The diversity of techniques and implemented protocols represents in overall an important amount of work which validates FLM waveguides as a promising platform of quantum information”.

      Schematic of the experimental setup


      On the other hand, how to decelerate the decoherence processes of electron-coupled nuclear spins in rare earth-ion-doped solids is of interest. The research team achieved a comprehensive enhancement of the population and coherence lifetimes of both the electron spins and the coupled nuclear spins in the sub-Kelvin temperature regime with compatibility of high-quality and fast manipulations. The measurements were based on pulsed electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy at temperatures down to 100 mK when the electron spins were almost fully polarized. The results demonstrated the suitability of deeply cooled paramagnetic rare-earth ions for memory components aimed at quantum communication and quantum computation.

      This work was published in Physical Review Applied on Feb 28th. The reviewerscommented on this as “A setup that is relatively rare world wide… The apparatus is likewise interesting, and will likely enable detailed spectroscopy of some systems in regimes that have been hard to access before ” and “To my knowledge this is the first observation of a strong increase of spin coherence times in rare-earth doped crystals by going to sub-Kelvin temperatures ”.

      Thermal-conduction components around and inside the ENDOR resonator


      Paper link:

      https://www.osapublishing.org/optica/abstract.cfm?uri=optica-7-2-192

      https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied



      (Written by YANG Ziyi, edited by LU Hongyu, USTC News Center)