Introduction of spin centers in single crystals of Ba₂CaWO_6-δ

Electronic spins are ideal qubit candidates both for their modularity and their ease of manipulation with microwave radiation. While fundamentally, T₂, the spin-spin relaxation time, represents the functional operating time of a qubit, T₁, the spin-lattice relaxation time, is ultimately the most restrictive parameter, as T₁ represents the theoretical upper limit to T₂. Design approaches to maximize T₁ remain an open question. We report the coherence properties of W⁵⁺ spin centers in Ba₂CaWO_6-δ generated by oxygen vacancies. We characterized these defects by measuring the T₁ and T₂ times from T = 5 to 150 K. Correlation of the T₁ lifetimes obtained from pulse EPR with phonon modes obtained from the heat capacity data quantifies the contribution of respective phonon modes to the spin-phonon coupling in the system. These results demonstrate that systematic defect generation in double perovskite structures can generate viable paramagnetic point centers for quantum applications.