Fast spin exchange across a multielectron mediator.

Malinowski, Filip K.; Martins, Frederico; Smith, Thomas B.; Bartlett, Stephen D.; Doherty, Andrew C.; Nissen, Peter D.; Fallahi, Saeed; Gardner, Geoffrey C.; Manfra, Michael J.; Marcus, Charles M.; Kuemmeth, Ferdinand

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. Controllable two-qubit interactions are necessary to build a functional quantum computer. Here the authors demonstrate fast, coherent swapping of two spin states mediated by a long, multi-electron quantum dot that could act as a tunable coupler mediating interactions between multiple qubits.

Nature Communications, 2019, Vol 10, Issue 1, p1

2041-1723

Academic Journal

10.1038/s41467-019-09194-x