Er3+:Y2SiO5 is a material of particular interest due to its compatibility in realizing telecom-band optical quantum memories and in the implementation of quantum transducers interfacing optical communication with quantum computers working in the microwave regime. Extending the coherence lifetimes of the electron spins and the nuclear spins is the essential prerequisite for implementing efficient quantum information processing. The electron spin coherence time of this material is so far limited to several microseconds, and there are significant challenges in optimizing coherence lifetimes simultaneously for both the electron and nuclear spins. Here we perform to our knowledge the first pulsed-ENDOR (Electron Nuclear DOuble Resonance) investigation for an Er3+-doped material at sub-Kelvin temperatures, based on a home-built sub-Kelvin pulsed ENDOR spectrometer. At the lowest working temperature, the electron spin coherence time reaches 273 us, which is enhanced by more than 40 times compared with the previous results. In the sub-Kelvin regime, a rapid increase in the nuclear spin coherence time is observed, and the longest coherence time of 738 us is obtained. These results are obtained with the compatibility of fast and efficient operations, which establish the foundation for quantum storage and quantum transduction from microwave to optical frequencies at telecom C-band.
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