Significance Modest magnetic fields above ≈ 22 T in the underdoped cuprates were argued to destroy superconductivity and reveal a conventional metallic pseudogap ground state that hosts quantum oscillations. We perform high-magnetic field electrical resistivity and magnetic torque measurements using low temperatures and small applied measurement currents to reveal instead an unconventional quantum vortex matter ground state that persists beyond the highest static magnetic fields. An alternative model is required to explain the coexistence of quantum oscillations with a robust d -wave superconducting gap in the newly uncovered quantum vortex matter ground state.