  In the present work, we report the new findings on the doping level
dependence of the phase coherence between superconducting
Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi-2212) grains. The experimental results
from the strongly underdoped and overdoped regimes deviated from the
expectation based on the doping level dependence of the superfluid density at
$T$ = 0 K. These findings appear to be governed by interplay between competing
orders inside the superconducting dome of cuprate superconductors. Two quantum
critical points are likely to exist at the underdoped and overdoped regimes
beneath the superconducting dome.
