The success of a quantum annealing algorithm requires a polynomial scaling of the energy gap. Recently it was shown that a two-dimensional transverse-field Ising model on a square lattice with nearest-neighbor $\pm J$ random coupling has a polynomial energy gap in the symmetric subspace of the parity operator [Nature (London) 631, 749 (2024)], indicating the efficient preparation of its ground states by quantum annealing. However, it is not clear if this result can be generalized to other spin glass models with continuous or biased randomness. Here we prove that under general independent and identical distributions of the exchange energies, the energy gap of a one-dimensional random transverse-field Ising model at the critical point, even without frustration, follows a stretched exponential scaling in the parity-restricted subspace. We discuss the implication of this result to quantum annealing problems.

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• Adiabatic quantum optimization
• Critical phenomena
• Random bond Ising model