Spin Qubits Candidate in Transition-Metal-Ion doped Halide Double Perovskites

Solid-state spin qubits offer a promising route toward scalable quantum technologies. Here we demonstrate that, despites of a nuclear-spin-rich host of halide double perovskites (HDPs), transition-metal centers (Cr³⁺ and Fe³⁺ ions) are a good candidate for spin qubits exhibiting long-lived electron spin coherence with $T_2$  = 29.5 µs and 21.2 µs at 4 K, respectively. Notably, spin localization facilitates a well-defined electron-nuclear (e-N) spin rotation between the electron spin and the neighboring nuclear spins of ^35,37Cl and¹³³Cs. The resulting e-N spin cluster is readily beneficial for a target nuclear-spin sensing. For the Cr³⁺ spin centers, the optical transitions associated with Cr³⁺ spin centers is spin-selective thereby paving a way for optical addressing of spins. Our findings from these spin ensemble studies establish HDPs as a new promising platform for creating solid-state spin qubits using simple and inexpensive solution-based single crystal growth methods, broadening material applications of halide perovskites.