Spin decoherence in a two-qubit CPHASE gate: the critical role of tunneling noise
Peihao Huang, Neil M. Zimmerman, Garnett W. Bryant
The rapid progress in the manipulation and detection of semiconductor spin qubits enables the experimental demonstration of a high fidelity two-qubit logic gate, which is necessary for universal quantum computing. Here, we study the decoherence of two electron spin qubits due to charge noise in a silicon double quantum dot (DQD) used for a two-qubit logic gate. We consider both detuning and tunneling fluctuations in the presence of $1/f$ charge noise. The qubit decoherence due to detuning and tunneling fluctuations show different detuning dependencies, and decoherence can be dominated by detuning fluctuation or tunneling fluctuation depending on the condition of detuning and the tunnel barrier. By comparing with recent two-qubit logic gate experiments, we find that the decoherence can be dominated by charge noise induced tunneling fluctuation and the admixture of charge states. We discussed the important implications of the findings for the noise reduction operation of a spin qubit.