  We present a way to quantum-disorder a pair density wave, and propose it to
be a candidate of the effective low-energy description of the pseudogap metal
which may reveal itself in a sufficiently high magnetic field that suppresses
the d-wave pairing. The ground state we construct is a small-pocket Fermi
liquid with a bosonic Mott insulator in the density-wave-enlarged unit cell. At
low energy, the charge density is mainly carried by charge 2e bosons, which
develop a small insulating gap. As an intermediate step, we discuss the quantum
disordering of a fully gapped superconductor and its excitation spectrum. In
order to illustrate the concepts we introduce, we introduce a simplified 1D
model which we solve numerically. We discuss a number of experimental
consequences. The interplay between the electron and the small-gap boson
results in a step function background in the electron spectral function which
may be consistent with existing ARPES data. Optical excitation across the boson
gap can explain the onset and the magnitude of the mid-infra-red absorption
reported long ago.
