Topological Phase Transition in a Frustrated Magnet Using a Superconducting Quantum Processor

We demonstrate a large-scale quantum simulation of a geometrically frustrated square-octagonal lattice using a programmable quantum processor of up to 1800 superconducting flux qubits. Our experiments provide evidence of a topological Kosterlitz-Thouless phase transition separating a paramagnet from a critical phase. Essential to the Kosterlitz-Thouless critical behaviour, we observe the emergence of a two-component order parameter with a continuous symmetry that originates from the interplay between frustration, thermal effects, and quantum fluctuations. We compare our results with quantum Monte Carlo simulations. These results and techniques may help pave the way towards future large-scale quantum simulations based upon superconducting flux qubits for problems that are impractical to simulate classically.