Center for Quantum Devices and Station Q Copenhagen, Niels Bohr Institute, University of Copenhagen, 2100, Copenhagen, Denmark.
Centre for Engineered Quantum Systems, School of Physics, The University of Sydney, Sydney, NSW, 2006, Australia.
Nat Commun. 2019 Mar 13;10(1):1196. doi: 10.1038/s41467-019-09194-x.
Scalable quantum processors require tunable two-qubit gates that are fast, coherent and long-range. The Heisenberg exchange interaction offers fast and coherent couplings for spin qubits, but is intrinsically short-ranged. Here, we demonstrate that its range can be increased by employing a multielectron quantum dot as a mediator, while preserving speed and coherence of the resulting spin-spin coupling. We do this by placing a large quantum dot with 50-100 electrons between a pair of two-electron double quantum dots that can be operated and measured simultaneously. Two-spin correlations identify coherent spin-exchange processes across the multielectron quantum dot. We further show that different physical regimes of the mediated exchange interaction allow a reduced susceptibility to charge noise at sweet spots, as well as positive and negative coupling strengths up to several gigahertz. These properties make multielectron dots attractive as scalable, voltage-controlled coherent coupling elements.
可扩展量子处理器需要可调谐的双量子比特门，这些门需要快速、相干且长程。海森堡交换相互作用为自旋量子比特提供了快速和相干的耦合，但本质上是短程的。在这里，我们通过使用多电子量子点作为介体来证明其范围可以增加，同时保持自旋-自旋耦合的速度和相干性。我们通过在一对可以同时操作和测量的双电子双量子点之间放置一个带有 50-100 个电子的大量子点来实现这一点。双自旋相关性确定了跨多电子量子点的相干自旋交换过程。我们进一步表明，介导的交换相互作用的不同物理状态允许在甜蜜点处降低对电荷噪声的敏感性，并且耦合强度可以达到几个千兆赫的正值和负值。这些特性使得多电子点成为有吸引力的可扩展、电压控制的相干耦合元件。
