  We present the first observation of dynamically modulated quantum phase
transition (QPT) between two distinct charge density wave (CDW) phases in
2-dimensional 2H-NbSe$_2$. There is recent spectroscopic evidence for the
presence of these two quantum phases, but its evidence in bulk measurements
remained elusive. We studied suspended, ultra-thin \nbse devices fabricated on
piezoelectric substrates - with tunable flakes thickness, disorder level and
strain. We find a surprising evolution of the conductance fluctuation spectra
across the CDW temperature: the conductance fluctuates between two precise
values, separated by a quantum of conductance. These quantized fluctuations
disappear for disordered and on-substrate devices. With the help of mean-field
calculations, these observations can be explained as to arise from dynamical
phase transition between the two CDW states. To affirm this idea, we vary the
lateral strain across the device via piezoelectric medium and map out the phase
diagram near the quantum critical point (QCP). The results resolve a
long-standing mystery of the anomalously large spectroscopic gap in NbSe$_2$.
