|q⟩ Bad Qubits

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Multiple choice
A qubit has T1 = 50 us and pure-dephasing time Tphi = 75 us, with 1/T2 = 1/(2 T1) + 1/Tphi. Starting from <X>(0) = 1, the coherence decays as <X>(t) = e^(-t/T2). What is <X> at t = 30 us?