Qubit spin ice

A reconfigurable spin ice Spin ices, magnetic systems in which local spins respect the so-called ice rules, can occur in natural materials or be engineered in patterned arrays. King et al. used superconducting qubits to implement a two-dimensional artificial spin ice. By changing the strength and ratio of spin couplings, the researchers were able to access a variety of ground states. Arranging the boundary spins in an antiferromagnetic configuration and then flipping one of those spins generated a magnetic monopole in the system's interior. Science, abe2824, this issue p. 576 A reconfigurable 2D spin ice is implemented on a quantum annealer based on superconducting qubits. Artificial spin ices are frustrated spin systems that can be engineered, in which fine tuning of geometry and topology has allowed the design and characterization of exotic emergent phenomena at the constituent level. Here, we report a realization of spin ice in a lattice of superconducting qubits. Unlike conventional artificial spin ice, our system is disordered by both quantum and thermal fluctuations. The ground state is classically described by the ice rule, and we achieved control over a fragile degeneracy point, leading to a Coulomb phase. The ability to pin individual spins allows us to demonstrate Gauss’s law for emergent effective monopoles in two dimensions. The demonstrated qubit control lays the groundwork for potential future study of topologically protected artificial quantum spin liquids.