Superconducting qubit circuit emulation of a vector spin-1/2

We propose a superconducting qubit circuit that can fully emulate a quantum vector spin-1/2, having three independent physical dipole moments whose operators obey the commutation relations of a vector angular momentum in the computational subspace. Each dipole moment couples to an independently-controllable external bias, emulating the Zeeman effect due to a fictitious, three-component vector magnetic field, and all three of these moments remain relatively constant over a broad range of emulated total fields around zero. This capability, combined with established techniques for two-qubit coupling, would enable for the first time the direct hardware emulation of nearly arbitrary quantum spin-1/2 systems, including the canonical Heisenberg model. In addition to its fundamental interest in condensed-matter physics, this would also constitute a crucial step towards important quantum information processing and quantum annealing capabilities that have so far been inaccessible to any available hardware. These include, for example, strong non-stoquastic interactions for quantum annealing, quantum error suppression, Hamiltonian and holonomic quantum computing, and adiabatic quantum chemistry.