  Ab initio calculations play an essential role in our fundamental
understanding of quantum many-body systems across many subfields, from strongly
correlated fermions to quantum chemistry and from atomic and molecular systems
to nuclear physics. One of the primary challenges is to perform accurate
calculations for systems where the interactions may be complicated and
difficult for the chosen computational method to handle. Here we address the
problem by introducing a new approach called wavefunction matching.
Wavefunction matching transforms the interaction between particles so that the
wavefunctions up to some finite range match that of an easily computable
interaction. This allows for calculations of systems that would otherwise be
impossible due to problems such as Monte Carlo sign cancellations. We apply the
method to lattice Monte Carlo simulations of light nuclei, medium-mass nuclei,
neutron matter, and nuclear matter. We use high-fidelity chiral effective field
theory interactions and find good agreement with empirical data. These results
are accompanied by new insights on the nuclear interactions that may help to
resolve long-standing challenges in accurately reproducing nuclear binding
energies, charge radii, and nuclear matter saturation in ab initio
calculations.
