Chiral superfluid phase in the triangular-lattice Bose-Hubbard model on a superconducting qubit quantum simulator

Superconducting qubits provide a promising platform for analog quantum simulation due to their natural implementation of the Bose-Hubbard Hamiltonian and flexibility in tuning system parameters. One of the simplest lattices with a rich quantum many-body phase diagram is the triangular ladder, due to its combination of geometric frustration, strong interactions, and low dimensionality [1].  Here, we present an experimental implementation of such a triangular lattice on a quantum simulator based on superconducting qubits. At half filling, we observe two ground state superfluid phases. In the absence of a synthetic magnetic field, the system exhibits a Meissner superfluid, with vanishing currents within the interior. With a nonzero uniform synthetic magnetic field, the chiral superfluid is characterized by alternating currents along the rungs of the ladder. We detect these phases by measuring correlations of currents across pairs of rungs, enabled by simultaneous readout on all of our lattice sites. We also demonstrate robustness of the phases by tuning the ratio of diagonal to parallel hopping in the lattice.

[1] Halati C-M and Giamarchi T 2023 Bose-hubbard triangular ladder in an artificial gauge field Phys. Rev. Res. 5 013126