Pulse Sequence Design for Crosstalk Mitigation

Surface code error correction leverages the property of Clifford transformation, where the quantum operations limited to these transformations are classically simulable. Hinging on this property of surface code, we can interlace the surface code circuit with quantum gates inside the Clifford group, without affecting the surface code error correction cycle. We call such artificially added gates pulse sequence, following the convention in NMR where it was first developed. The main idea of pulse sequence design is to transform the frame of unwanted error periodically such that on average, these quantum errors destructively interfere and thus cancel out.  Unwanted crosstalks and dephasing are detrimental to surface code. Pulse sequence can be utilized to cancel out both error mechanisms. We propose new pulse sequence candidates based on physical analysis of possible crosstalk and dephasing error properties. It is the first pulse sequence design that can cancel crosstalk between all qubit pairs of any distance. We also benchmark various pulse sequence proposals in a realistic simulation of surface code.