All-optical control of long-lived nuclear spins in rare-earth doped nanoparticles

Nanoscale systems that coherently couple to light and possess spins offer key capabilities for quantum technologies. However, an outstanding challenge is to preserve properties, and especially optical and spin coherence lifetimes, at the nanoscale. Here, we report optically controlled nuclear spins with long coherence lifetimes (T2) in rare-earth-doped nanoparticles. We detect spins echoes and measure a spin coherence lifetime of 2.9 ± 0.3 ms at 5 K under an external magnetic field of 9 mT, a T2 value comparable to those obtained in bulk rare-earth crystals. Moreover, we achieve spin T2 extension using all-optical spin dynamical decoupling and observe high fidelity between excitation and echo phases. Rare-earth-doped nanoparticles are thus the only nano-material in which optically controlled spins with millisecond coherence lifetimes have been reported. These results open the way to providing quantum light-atom-spin interfaces with long storage time within hybrid architectures

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All-optical dynamical decoupling. a CPMG sequence with optical 2-color excitation and rephasing π pulses. The initial excitation pulse has a Y phase and the π pulses an X phase. This is obtained by varying the relative phase between the two frequency components of the optical pulses. b Echo decays (circles) for different initial phases and exponential fits (lines). A much lower T2DD is observed for an X initial phase (~1.0 ms) than for an Y one (~3.0 ms). This is due to the accumulation of pulse errors and confirms that our DD sequence behaves as a CPMG one. c Spin-echo decays (circles) obtained for τDD = 150, 200 and 300 µs with n ≤ 60, and exponential fits (lines). d Experimental (circles) and modelled (line) T2DD evolution as a function of τDD. (see Supplementary Fig. 5). The data point represented by the black circle was discarded for the fit. e Spin-echo decays (circles) with and without a weak magnetic field. Solid line: exponential fits. Error bars and uncertainties correspond to ±1 standard error