Quantum spin networks having engineered geometries and interactions are eagerly pursued for quantum simulation and access to emergent quantum phenomena such as spin liquids. Spin-1/2 centers are particularly desirable because they readily manifest coherent quantum fluctuations. Here we introduce a controllable spin-1/2 architecture consisting of titanium atoms on a magnesium oxide surface. We tailor the spin interactions by atomic-precision positioning using a scanning tunneling microscope (STM), and subsequently perform electron spin resonance (ESR) on individual atoms to drive transitions into and out of quantum eigenstates of the coupled-spin system. Interactions between the atoms are mapped over a range of distances extending from highly anisotropic dipole coupling, to strong exchange coupling. The local magnetic field of the magnetic STM tip serves to precisely tune the superposition states of a pair of spins. The precise control of the spin-spin interactions and ability to probe the states of the coupled-spin network by addressing individual spins will enable exploration of quantum many-body systems based on networks of spin-1/2 atoms on surfaces.
@article{arxiv.1712.04082,
title = {Engineering the eigenstates of coupled spin-1/2 atoms on a surface},
author = {Kai Yang and Yujeong Bae and William Paul and Fabian D. Natterer and Philip Willke and Jose L. Lado and Alejandro Ferrón and Taeyoung Choi and Joaquín Fernández-Rossier and Andreas J. Heinrich and Christopher P. Lutz},
journal= {arXiv preprint arXiv:1712.04082},
year = {2017}
}