University of New Mexico

Ground-state calculations for the two-dimensional Fermi–Hubbard model have been stuck on a basis mismatch: momentum-space matrix product states are compact, while the diagonal correlators that capture short-range correlation act naturally in real space. The new scheme has a quantum processor prepare and rotate a bond-dimension-4 momentum-space matrix product state, sample in bases fixed by the Hamiltonian, and optimize the correlator entirely in classical post-processing with no quantum-classical feedback loop. On 32 qubits of Quantinuum's H2-2, postselection gives a 4.40% relative ground-state energy error for the half-filled lattice, reduced further by calibration using low-order moments from the matrix product state.

Ground-state calculations for the two-dimensional Fermi–Hubbard model have been stuck on a basis mismatch: momentum-space matrix product states are compact, while the diagonal correlators that capture short-range correlation act naturally in real space. The new scheme has a quantum processor prepare and rotate a bond-dimension-4 momentum-space matrix product state, sample in bases fixed by the Hamiltonian, and optimize the correlator entirely in classical post-processing with no quantum-classical feedback loop. On 32 qubits of Quantinuum's H2-2, postselection gives a 4.40% relative ground-state energy error for the half-filled lattice, reduced further by calibration using low-order moments from the matrix product state.