Figure 3: DSCB-mediated coherent coupling of spatially separated NV registers.
From: Scalable architecture for a room temperature solid-state quantum information processor
(a) Adiabatic sequential swap along the vertical direction, parallel to the magnetic field gradient. Individual addressing of impurities, enabled by the field gradient, allows for a slow ramping of the Rabi frequencies Ωi and Ωj through one another; this achieves adiabatic swap of the quantum states of the two impurities through rapid adiabatic passage. Thus, sequential adiabatic swap of quantum states along the spin chain can be achieved by successively tuning individual Rabi frequencies across one another. (b) FFST in the horizontal direction, transverse to the magnetic field gradient. The coupling strength between the end qubits and the spin chain is g, whereas the interchain coupling strength is κ. Schematic representation of the level structure of the NV electronic spin and a dark impurity spin. Controlling the NV-impurity coupling g is an essential component of FFST and occurs by driving the NV in two-photon resonance, with Rabi frequency Ω and detuning Δ. (c) Schematic circuit diagram outlining the protocol to achieve coherent coupling between the nuclear memory qubits of spatially separated NV registers. First, the nuclear and electronic qubits of a single register are swapped. Next, the electronic qubits of the two NV centres to be coupled are swapped through the DSCB. Finally, a two-qubit gate between the electronic and nuclear spin of the second register is performed, before the memory qubit is returned to the nuclear spin of the original NV centre.
