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

Abstract

Nanoscale systems offer key capabilities for quantum technologies that include single qubit control and readout, multiple qubit gate operation, extremely sensitive and localized sensing and imaging, as well as the ability to build hybrid quantum systems. To fully exploit these functionalities, multiple degrees of freedom are highly desirable: in this respect, nanoscale systems that coherently couple to light and possess spins, allow for storage of photonic qubits or light-matter entanglement together with processing capabilities. In addition, all-optical control of spins can be possible for faster gate operations and higher spatial selectivity compared to direct RF excitation. Such systems are therefore of high interest for quantum communications and processing. However, an outstanding challenge is to preserve properties, and especially optical and spin coherence lifetimes, at the nanoscale. Indeed, interactions with surfaces related perturbations strongly increase as sizes decrease, although the smallest objects present the highest flexibility for integration with other systems. Here, we demonstrate optically controlled nuclear spins with long coherence lifetimes (T2) in rare earth doped nanoparticles. We observed spins echoes and measured T2 of 2.9 +/- 0.3 ms at 5 K and under a magnetic field of 9 mT, a value comparable to those obtained in bulk single crystals. Moreover, we achieve, for the first time, 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 reported nano-materials in which optically controlled spins with millisecond coherence lifetimes have been observed. These results open the way to providing quantum light-atom-spin interfaces with long storage time within hybrid architectures.