sciencemag | Entanglement is a key resource for quantum computers, quantum-communication networks, and high-precision sensors.
Macroscopic spin ensembles have been historically important in the development of quantum algorithms for
these prospective technologies and remain strong candidates for implementing them today. This strength derives
from their long-lived quantum coherence, strong signal, and ability to couple collectively to external degrees of freedom.
Nonetheless, preparing ensembles of genuinely entangled spin states has required high magnetic fields and
cryogenic temperatures or photochemical reactions. We demonstrate that entanglement can be realized in solid-state
spin ensembles at ambient conditions. We use hybrid registers comprising of electron-nuclear spin pairs that are localized
at color-center defects in a commercial SiC wafer. We optically initialize 103 identical registers in a 40-mm3 volume
(with 0:95þ0:05 −0:07 fidelity) and deterministically prepare them into the maximally entangled Bell states (with 0.88 ± 0.07
fidelity). To verify entanglement, we develop a register-specific quantum-state tomography protocol. The entanglement
of a macroscopic solid-state spin ensemble at ambient conditions represents an important step toward practical
quantum technology
