Quantum charge-4e state in the SU(4) Hubbard Model

Unlike conventional charge-2e superconductors, a charge-4e superconducting state exhibits long-range coherence of electron quartets rather than pairs. Owing to the strongly correlated nature of this exotic state, previous studies have mostly relied on mean-field approximations, leaving the quantum phase transition between charge-2e and charge-4e superconductivity unexplored. Here, we investigate the quantum charge-4e phase in the attractive SU(4) Hubbard model at one-quarter filling using sign-problem-free determinant quantum Monte Carlo (DQMC) simulations. By employing a recently developed exact bridge link method within DQMC, we overcome the challenge of an infinite-variance problem in the charge-4e phase and identify a quantum phase transition between the conventional charge-2e superconducting phase and the charge-4e superconducting phase. Remarkably, analysis of the critical behavior suggests that the transition may belong to a deconfined quantum critical point with an emergent non-Abelian Sp(2) gauge field.