含噪量子过程的对称性刻画
Symmetrised Characterisation of Noisy Quantum Processes
摘要：
开发多体量子系统的高精度控制的一个主要目标是实现它们作为量子计算机的潜力。在这个方向上最大的障碍可能是“退相干”问题：量子系统对环境噪声和其他控制限制的极端脆弱性。容错量子纠错理论已经表明，只要影响量子系统的噪声满足某些明确定义的理论条件，即使存在退相干，量子计算也是可能的。然而，现有的噪声表征方法已经变得棘手的系统，在今天的实验室控制。在本文中，我们介绍了一种基于对称性的技术，使直接的实验表征的关键属性的退相干影响多体量子系统。我们的方法减少了现有的方法所需的实验次数从指数多项式的子系统的数量。我们证明了这种技术的应用，在固态核自旋的控制优化。
英文摘要：
A major goal of developing high-precision control of many-body quantum systems is to realise their potential as quantum computers. Probably the most significant obstacle in this direction is the problem of "decoherence": the extreme fragility of quantum systems to environmental noise and other control limitations. The theory of fault-tolerant quantum error correction has shown that quantum computation is possible even in the presence of decoherence provided that the noise affecting the quantum system satisfies certain well-defined theoretical conditions. However, existing methods for noise characterisation have become intractable already for the systems that are controlled in today's labs. In this paper we introduce a technique based on symmetrisation that enables direct experimental characterisation of key properties of the decoherence affecting a multi-body quantum system. Our method reduces the number of experiments required by existing methods from exponential to polynomial in the number of subsystems. We demonstrate the application of this technique to the optimisation of control over nuclear spins in the solid state.
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