Proximal quantum control of spin and spin ensemble with localized control field from skyrmions

Selective control of individual spin qubits is needed for scalable quantum computing based on spin states. Achieving high-fidelity in both single-qubit and two-qubit gates, essential components of universal quantum computers, necessitates highly localized control fields. These fields must be capable of addressing specific spin qubits while minimizing gate errors and crosstalk in adjacent qubits. Overcoming the challenge of generating a localized radio-frequency magnetic field, in the absence of elementary magnetic monopoles, we introduce a technique that combines divergent and convergent nanoscale magnetic skyrmions. This approach produces a precise control field that manipulates spin qubits with high fidelity. We propose the use of 2D skyrmions, which are much easier to fabricate than 3D hedgehog structures. The latter are considered emergent magnetic monopoles, but their fabrication is challenging. In contrast, 2D skyrmions can be created with use of standard semiconductor-foundry processes and offer effective magnetic field confinement in two dimensions. Our comparative analysis of the density-matrix evolution and gate fidelities in scenarios involving proximal skyrmions and nanomagnets indicates potential gate fidelities surpassing 99.95% for $\ensuremath{\pi}/2$ gates and 99.90% for $\ensuremath{\pi}$ gates. The average field induced at the nearest neighboring qubit by skyrmions is 0.0332 mT along the $x$ axis (200 nm), while it is 0.507 mT for the nanomagnet case. Notably, the skyrmion configuration generates a significantly lower field on neighboring spin qubits, i.e., 15 times smaller field or approximately $23.5$ dB compared to nanomagnets that produce the same field at the target qubit, making it a more-suitable candidate for scalable quantum control architectures by reducing disturbances in adjacent qubits.