大规模量子计算的资源成本
The resource cost of large scale quantum computing
摘要：
本文研究了容错量子计算的可扩展性问题。这个问题是在估计建立这种计算机所需资源的角度下研究的。原则上，我们所说的资源是非常普遍的;它可以是功率，能量，分配给不同量子位的总带宽。然而，我们主要关注量子计算的能量成本。特别是，我们开发了一种跨学科的方法，可以最大限度地减少在量子计算机上实现算法所需的资源。通过要求在算法提供具有目标准确度的正确答案的约束下找到执行计算所需的最小资源量，可以优化整个计算机以最小化所花费的资源，同时确保具有高概率的正确答案。我们将这种方法应用于一个基于超导量子比特的完整模型容错量子计算机。我们的研究结果表明，对于在数千个逻辑量子比特上实现的算法，我们的方法使得有可能在不优化的情况下将能量成本降低几个数量级，功耗可能接近千兆瓦。这项工作表明，量子计算的能量成本本身应该是一个标准，允许评估给定量子计算机技术的缩放潜力。它还表明，通过跨学科方法优化量子计算机的架构，包括算法，纠错，量子位物理，工程方面，例如我们提出的那些，可以证明是一个强大的工具，明显提高量子计算机的缩放潜力。最后，我们提供了关于如何使容错量子计算机节能的一般提示。
英文摘要：
This thesis deals with the problematics of the scalability of fault-tolerant quantum computing. This question is studied under the angle of estimating the resources needed to set up such computers. What we call a resource is, in principle, very general; it could be the power, the energy, the total bandwidth allocated to the different qubits... However, we mainly focus on the energetic cost of quantum computing. In particular, we develop an inter-disciplinary approach that allows to minimize the resources required to implement algorithms on quantum computers. By asking to find the minimum amount of resources required to perform a computation under the constraint that the algorithm provides a correct answer with a targeted accuracy, it is possible to optimize the whole computer in order to minimize the resources spent, while being sure to have a correct answer with a high probability. We apply this approach to a complete model fault-tolerant quantum computer based on superconducting qubits. Our results indicate that for algorithms implemented on thousands of logical qubits, our method makes it possible to reduce the energetic cost by orders of magnitudes in regimes where, without optimizing, the power consumption could be close to the gigawatt. This work illustrates that the energetic cost of quantum computing should be a criterion in itself, allowing to evaluate the scaling potential of a given quantum computer technology. It also illustrates that optimizing the architecture of a quantum computer, via inter-disciplinary methods, including algorithms, error correction, qubit physics, engineering aspects, such as the ones that we propose, can prove to be a powerful tool, clearly improving the scaling potential of quantum computers. Finally, we provide general hints about how to make fault-tolerant quantum computers energy efficient.
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