  We develop a class of soliton solution of {\it linear} Schr\"odinger equation
without external potential. The quantum probability density generates its own
boundary inside which there is internal vibration whose wave number is
determined by the velocity of the particle as firstly conjectured by de
Broglie. Assuming resonance of the internal vibration will lead to quantization
of particle's momentum in term of wave number of the envelope quantum
probability density. We further show that the linearity of the Schr\"odinger
equation allows us to have non-interacting many solitons solution through
superposition, each describing a particle with equal mass.
