论文标题

在部分错误校正时代,干净和肮脏的Qubit战役

The battle of clean and dirty qubits in the era of partial error correction

论文作者

Bultrini, Daniel, Wang, Samson, Czarnik, Piotr, Gordon, Max Hunter, Cerezo, M., Coles, Patrick J., Cincio, Lukasz

论文摘要

当可能进行误差校正时,有必要将大量物理Qubt分配给每个逻辑量子。错误校正可以运行更深的电路,但是每个附加物理量子都可以潜在地增加计算空间的指数增加,因此在使用量子器进行误差校正或将其用作嘈杂的Qubits之间存在权衡。在这项工作中,我们查看使用嘈杂的Qubits与无噪声量子(一种理想化的错误校正量子)结合使用的效果,我们称之为“清洁和脏”设置。我们采用分析模型和数值模拟来表征此设置。从数值上讲,我们显示了噪声引起的贫瘠的高原(Nibps)的外观,即在伊辛型模型汉密尔顿变异的ANSATZ电路中,由噪声引起的可观察到的指数浓度。即使只有一个值在嘈杂并给出了足够深的电路,我们也会观察到这一点,这表明nibps不能仅仅通过误差校正量子的子集来完全克服。在正面,我们发现,对于电路中的每个无噪声量子,在梯度可观察物的浓度中都有指数抑制,显示了部分误差校正的益处。最后,我们的分析模型通过表明可观察到与肮脏量子量比比例相关的指数中的缩放量表来证实了这些发现。

When error correction becomes possible it will be necessary to dedicate a large number of physical qubits to each logical qubit. Error correction allows for deeper circuits to be run, but each additional physical qubit can potentially contribute an exponential increase in computational space, so there is a trade-off between using qubits for error correction or using them as noisy qubits. In this work we look at the effects of using noisy qubits in conjunction with noiseless qubits (an idealized model for error-corrected qubits), which we call the "clean and dirty" setup. We employ analytical models and numerical simulations to characterize this setup. Numerically we show the appearance of Noise-Induced Barren Plateaus (NIBPs), i.e., an exponential concentration of observables caused by noise, in an Ising model Hamiltonian variational ansatz circuit. We observe this even if only a single qubit is noisy and given a deep enough circuit, suggesting that NIBPs cannot be fully overcome simply by error-correcting a subset of the qubits. On the positive side, we find that for every noiseless qubit in the circuit, there is an exponential suppression in concentration of gradient observables, showing the benefit of partial error correction. Finally, our analytical models corroborate these findings by showing that observables concentrate with a scaling in the exponent related to the ratio of dirty-to-total qubits.

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