  High-$T_c$ superconductivity is unconventional because the gap is not
isotropic as in simple metals but has $d_{x^2-y^2}$ symmetry with lines of
nodes. In a fascinating thermal transport experiment on a high-$T_c$
superconductor, Krishana et al \cite{Krishana} have reported mysterious
magnetic field induced first order transitions from a superconducting state
with gap nodes to a state without gap nodes. We show here that this is an
experimental manifestation of a novel {\it macroscopic} quantum phenomenon
induced by the magnetic field, qualitatively different from the usual quantum
Hall effects. It corresponds to the {\it quantization of the superfluid
density} in a superconductor with gap nodes due to the generation of Confined
Field Induced Density Waves (CFIDW) in the node regions of the Fermi surface.
The Landau numbers $L$ are not sufficient to index these macroscopic quantum
states and the addition of a new quantum number $\zeta$ is necessary. Distinct
qualitative implications of this non-integer $|L,\zeta>$ quantization are also
evident in a number of recent unexplained experimental reports in the cuprates.
