Estimating the Effect of Crosstalk Error on Circuit Fidelity Using Noisy
  Intermediate-Scale Quantum Devices
Current advancements in technology have focused the attention of the quantum
computing community toward exploring the potential of near-term devices whose
computing power surpasses that of classical computers in practical
applications. An unresolved central question revolves around whether the
inherent noise in these devices can be overcome or whether any potential
quantum advantage would be limited. There is no doubt that crosstalk is one of
the main sources of noise in noisy intermediate-scale quantum (NISQ) systems,
and it poses a fundamental challenge to hardware designs. Crosstalk between
parallel instructions can corrupt quantum states and cause incorrect program
execution. In this study, we present a necessary analysis of the crosstalk
error effect on NISQ devices. Our approach is extremely straightforward and
practical to estimate the crosstalk error of various multi-qubit devices. In
particular, we combine the randomized benchmarking (RB) and simultaneous
randomized benchmarking (SRB) protocol to estimate the crosstalk error from the
correlation controlled-NOT (CNOT) gate. We demonstrate this protocol
experimentally on 5-, 7-, \& 16-qubit devices. Our results demonstrate the
crosstalk error model of three different IBM quantum devices over the
experimental week and compare the error variation against the machine, number
of qubits, quantum volume, processor, and topology. We then confirm the
improvement in the circuit fidelity on different benchmarks by up to 3.06x via
inserting an instruction barrier, as compared with an IBM quantum noisy device
which offers near-optimal crosstalk mitigation in practice. Finally, we discuss
the current system limitation, its tradeoff on fidelity and depth, noise beyond
the NISQ system, and mitigation opportunities to ensure that the quantum
operation can perform its quantum magic undisturbed.
Sovanmonynuth Heng Myeongseong Go Youngsun Han