Quantum Volume is a full-stack benchmark for near-term quantum computers. It quantifies the largest size of a square circuit which can be executed on the target device with reasonable fidelity. Error mitigation is a set of techniques intended to remove the effects of noise present in the computation of noisy quantum computers when computing an expectation value of interest. Effective quantum volume is a proposed metric that applies error mitigation to the quantum volume protocol in order to evaluate the effectiveness not only of the target device but also of the error mitigation algorithm. Digital Zero-Noise Extrapolation (ZNE) is an error mitigation technique that estimates the noiseless expectation value using circuit folding to amplify errors by known scale factors and extrapolating to the zero-noise limit. Here we demonstrate that ZNE, with global and local unitary folding with fractional scale factors, in conjunction with dynamical decoupling, can increase the effective quantum volume over the vendor-measured quantum volume. Specifically, we measure the effective quantum volume of four IBM Quantum superconducting processor units, obtaining values that are larger than the vendor-measured quantum volume on each device. This is the first such increase reported.

翻译：量子体积是近期量子计算机的全栈基准测试，用于量化在目标设备上能以合理保真度执行的最大方形电路规模。误差缓解是一组旨在消除噪声量子计算机在计算感兴趣期望值时运算中噪声影响的技术。有效量子体积是一种提出的度量标准，它将误差缓解应用于量子体积协议，以评估目标设备及误差缓解算法的有效性。数字零噪声外推（ZNE）是一种误差缓解技术，通过使用电路折叠以已知比例因子放大误差并外推至零噪声极限来估计无噪声期望值。本文演示了在结合动态解耦的情况下，采用全局与局部幺正折叠及分数比例因子的ZNE能够提升供应商测量的量子体积所对应的有效量子体积。具体而言，我们在四个IBM量子超导处理器单元上测量了有效量子体积，获得的数值均大于各设备上供应商测量的量子体积。这是首次报道此类提升。