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Single-qubit gates are essential components of a universal quantum computer. Without selective addressing of individual qubits, scalable implementation of quantum algorithms is extremely challenging. When the qubits are discrete points or regions on a lattice, selectively addressing magnetic spin qubits at the nanoscale remains a challenge due to the difficulty of localizing and confining a classical divergence-free field to a small volume of space. Herein we propose a technique for addressing spin qubits using voltage-control of nanoscale magnetism, exemplified by the use of voltage control of magnetic anisotropy. We show that by tuning the frequency of the nanomagnet’s electric field drive to the Larmor frequency of the spins confined to a nanoscale volume, and by modulating the phase of the drive, single-qubit quantum gates with fidelities approaching those for fault-tolerant quantum computing can be implemented. Such single-qubit gate operations require only tens of femto-Joules per gate operation and have lossless, purely magnetic field control. Their physical realization is also straightforward using foundry manufacturing techniques.

 

The Dobryakov–Lebedev relation (Sov Phys Doklady 13:873, 1969), which relates the line width of the first-derivative of a Gaussian–Lorentzian convolution to the line widths of its Gaussian and Lorentzian components for an unresolved EPR line, is extended to resolved lines. Applying this extension to nitroxide-free radicals in solutions of low-viscosity solvents offers an opportunity to study interactions of the spins with the microwave field and spin–spin interactions previously inaccessible except by tedious numerical methods.