  Quantum computing is believed to be particularly useful for the simulation of
chemistry and materials, among the various applications. In recent years, there
have been significant advancements in the development of near-term quantum
algorithms for quantum simulation, including VQE and many of its variants.
However, for such algorithms to be useful, they need to overcome several
critical barriers including the inability to prepare high-quality
approximations of the ground state. Current challenges to state preparation,
including barren plateaus and the high-dimensionality of the optimization
landscape, make state preparation through ansatz optimization unreliable. In
this work, we introduce the method of ground state boosting, which uses a
limited-depth quantum circuit to reliably increase the overlap with the ground
state. This circuit, which we call a booster, can be used to augment an ansatz
from VQE or be used as a stand-alone state preparation method. The booster
converts circuit depth into ground state overlap in a controllable manner. We
numerically demonstrate the capabilities of boosters by simulating the
performance of a particular type of booster, namely the Gaussian booster, for
preparing the ground state of $N_2$ molecular system. Beyond ground state
preparation as a direct objective, many quantum algorithms, such as quantum
phase estimation, rely on high-quality state preparation as a subroutine.
Therefore, we foresee ground state boosting and similar methods as becoming
essential algorithmic components as the field transitions into using early
fault-tolerant quantum computers.
