超导与量子计算

Superconductivity meets quantum computation

基于量子力学态叠加性和纠缠性的量子计算,以其指数级增长的庞大计算空间和更高级的信息抽象能力,为计算提供了新的范式。这一新技术有可能解决一些经典计算无法解决的计算难题,同时解决经典计算的功耗问题。超导效应作为一种宏观量子效应,为量子态相干操控提供了绝佳的无损耗环境,而约瑟夫森结为构建量子比特提供了必要的能级分立性和非线性。经过二十余年的高速发展,基于超导量子电路的量子计算技术已经在退相干时间、量子态操控和读取、量子比特间可控耦合、中大规模扩展等关键技术上取得大量突破,成为构建通用量子计算机和量子模拟机最有前途的候选技术路线之一。文章就这一技术做一个简要的介绍和梳理,以令读者了解整个技术脉络为目标,尽可能不涉及复杂的符号和公式。最后,还简要讨论了超导量子计算发展的未来,并指出其中部分关键技术难点。

Quantum computation, based on quantum state superposition and entanglement, offered a new computing schema for its exponentially grown huge computing space and higher information abstracting ability. It can potentially solve a series of problems that is "hard" for classical computer, and significantly decrease the power consumption per operation. Superconductivity, as a robust macroscopic quantum phenomenon, offered a perfect non-dissipating test-bed for coherent quantum operation. Moreover, Josephson junction that based on superconductors offered essential state quantization and non-linearity for constructing a qubit. After over twenty year’s fast development, quantum computing technology based on superconducting quantum circuits has achieved abundant breaks in some key technologies, including improvement of coherence time, quantum state manipulation and readout, tunable coupling between qubits, scaling up to well addressable moderate-large scale quantum system, and so on. Now, it is no doubt that superconducting quantum computing becomes one of the most promising candidates for building a universal quantum computer. Here I would like to give a crash review for this technology, and briefly draw a skeleton of superconducting quantum circuits. The purpose is to let the readers catch some scientific backend for building a quantum computer. Therefore, I try the best to avoid complicated symbols and equations. Finally, I try to give a bold discussion about the future development blueprint, and point out some key technical challenges when approaching such a "Holy Grail".