  Inspired by the recent quantum oscillation measurement on the kagom\'{e}
lattice antiferromagnet in finite magnetic fields, we raise the question about
the physical contents of the emergent fermions and the gauge fields if the U(1)
spin liquid is relevant for the finite-field kagom\'{e} lattice
antiferromagnet. Clearly, the magnetic field is non-perturbative in this
regime, and the finite-field state has no direct relation with the U(1) Dirac
spin liquid proposal at zero field. Based on the dual vortex theory, we here
propose that, the $S^z$ magnetization is the emergent U(1) gauge flux, and the
fermionized dual vortex is the emergent fermion. In this formalism, the
magnetic field polarizes the spin component along the field direction that
modulates the U(1) flux for the fermionized vortices and generates the quantum
oscillation. Within the mean-field theory, we further discuss gauge field
correlation, vortex-antivortex continuum and thermal Hall effect. We expect
this work to provide a bit insight for the magnetized kagom\'{e} spin liquids.
