Centre for Quantum Computation and Communication Technology, School of Electrical Engineering and Telecommunications, The University of New South Wales, Sydney, New South Wales 2052, Australia.
School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.
Nature. 2015 Oct 15;526(7573):410-4. doi: 10.1038/nature15263. Epub 2015 Oct 5.
Quantum computation requires qubits that can be coupled in a scalable manner, together with universal and high-fidelity one- and two-qubit logic gates. Many physical realizations of qubits exist, including single photons, trapped ions, superconducting circuits, single defects or atoms in diamond and silicon, and semiconductor quantum dots, with single-qubit fidelities that exceed the stringent thresholds required for fault-tolerant quantum computing. Despite this, high-fidelity two-qubit gates in the solid state that can be manufactured using standard lithographic techniques have so far been limited to superconducting qubits, owing to the difficulties of coupling qubits and dephasing in semiconductor systems. Here we present a two-qubit logic gate, which uses single spins in isotopically enriched silicon and is realized by performing single- and two-qubit operations in a quantum dot system using the exchange interaction, as envisaged in the Loss-DiVincenzo proposal. We realize CNOT gates via controlled-phase operations combined with single-qubit operations. Direct gate-voltage control provides single-qubit addressability, together with a switchable exchange interaction that is used in the two-qubit controlled-phase gate. By independently reading out both qubits, we measure clear anticorrelations in the two-spin probabilities of the CNOT gate.
量子计算需要能够以可扩展的方式耦合的量子位，以及通用且高保真的单量子位和双量子位逻辑门。存在许多量子位的物理实现，包括单光子、囚禁离子、超导电路、单个缺陷或金刚石和硅中的原子，以及半导体量子点，其单量子位保真度超过容错量子计算所需的严格阈值。尽管如此，由于半导体系统中耦合量子位和退相的困难，迄今为止，使用标准光刻技术制造的高保真度的固态双量子位门仅限于超导量子位。在这里，我们提出了一种双量子位逻辑门，它使用同位素富集硅中的单自旋，并通过在量子点系统中使用交换相互作用来执行单量子位和双量子位操作来实现，就像在 Loss-DiVincenzo 提案中所设想的那样。我们通过结合单量子位操作的受控相位操作来实现 CNOT 门。直接栅极电压控制提供了单量子位可寻址性，以及用于双量子位受控相位门的可切换交换相互作用。通过独立读取两个量子位，我们测量了 CNOT 门的两个自旋概率的明显反相关。
