Electrical control of a solid-state flying qubit

Abstract: Solid-state approaches to quantum information technology are attractive because they are scalable. The coherent transport of quantum information over large distances, as required for a practical quantum computer, has been demonstrated by coupling solid-state qubits to photons1. As an alternative approach for a spin-based quantum computer, single electrons have also been transferred between distant quantum dots in times faster than their coherence time2, 3. However, there have been no demonstrations to date of techniques that can coherently transfer scalable qubits and perform quantum operations on them at the same time. The resulting so-called flying qubits are attractive because they allow for control over qubit separation and non-local entanglement with static gate voltages, which is a significant advantage over other solid-state qubits in confined systems for integration of quantum circuits. Here we report the transport and manipulation of qubits over distances of 6 microns within 40 ps, in an Aharonov-Bohm ring connected to two-channel wires that have a tunable tunnel coupling between channels. The flying qubit state is defined by the presence of a travelling electron in either channel of the wire, and can be controlled without a magnetic field. Our device has shorter quantum gates, longer coherence lengths (~86 {\mu}m at 70 mK), and shorter operation times (~10 ps or 100 GHz) than other solid-state flying qubit implementations4, 5, which makes our solid-state flying qubit potentially scalable.