Centre of Excellence for Quantum Computation and Communication Technology, School of Physics, University of New South Wales, Sydney, New South Wales, Australia.
Nature. 2019 Jul;571(7765):371-375. doi: 10.1038/s41586-019-1381-2. Epub 2019 Jul 17.
Electron spin qubits formed by atoms in silicon have large (tens of millielectronvolts) orbital energies and weak spin-orbit coupling, giving rise to isolated electron spin ground states with coherence times of seconds. High-fidelity (more than 99.9 per cent) coherent control of such qubits has been demonstrated, promising an attractive platform for quantum computing. However, inter-qubit coupling-which is essential for realizing large-scale circuits in atom-based qubits-has not yet been achieved. Exchange interactions between electron spins promise fast (gigahertz) gate operations with two-qubit gates, as recently demonstrated in gate-defined silicon quantum dots. However, creating a tunable exchange interaction between two electrons bound to phosphorus atom qubits has not been possible until now. This is because it is difficult to determine the atomic distance required to turn the exchange interaction on and off while aligning the atomic circuitry for high-fidelity, independent spin readout. Here we report a fast (about 800 picoseconds) [Formula: see text] two-qubit exchange gate between phosphorus donor electron spin qubits in silicon using independent single-shot spin readout with a readout fidelity of about 94 per cent on a complete set of basis states. By engineering qubit placement on the atomic scale, we provide a route to the realization and efficient characterization of multi-qubit quantum circuits based on donor qubits in silicon.
由硅原子中的电子自旋形成的量子比特具有较大的（数十毫电子伏特）轨道能量和较弱的自旋轨道耦合，从而产生具有秒级相干时间的孤立电子自旋基态。已经证明了这种量子比特的高保真度（超过 99.9%）相干控制，为量子计算提供了有吸引力的平台。然而，对于基于原子的量子比特实现大规模电路所必需的量子比特间耦合尚未实现。电子自旋之间的交换相互作用有望实现具有双量子比特门的快速（千兆赫）门操作，最近在栅极定义的硅量子点中已经证明了这一点。然而，直到现在，还不可能在两个磷原子量子比特束缚的电子之间创建可调节的交换相互作用。这是因为很难在为了实现高保真度、独立的自旋读出而对准原子电路的同时，确定打开和关闭交换相互作用所需的原子距离。在这里，我们使用独立的单次自旋读出报告了一种快速（约 800 皮秒）[公式：见文本]硅中磷施主电子自旋量子比特之间的双量子比特交换门，读出保真度约为 94%在完整的基态集上。通过在原子尺度上设计量子比特的位置，我们为基于硅中施主量子比特的多量子比特量子电路的实现和有效特性提供了一种途径。
