Spin decoherence in a quantum dot due to micro-magnets

A spin qubit in a semiconductor quantum dot is a promising candidate for quantum information processing for scalability and miniaturization. Micro-magnets have been proven to be effective to mediate the coupling of a spin qubit to photon and electrical control field. In this work, we study spin decoherence in a quantum dot mediated by the magnetic field gradient created by micro-magnets. The spin relaxation mediated by magnetic field gradient shows different magnetic field dependence compare with spin relaxation mediated by spin-orbit coupling. Furthermore, to the first order of the magnetic field gradient, there is finite spin dephasing due to 1/f charge noise. We discuss the consequence of the new spin decoherence mechanisms on the number of qubit operations.