  Improving the phase resolution of interferometry is crucial for
high-precision measurements of various physical quantities. Systematic phase
errors dominate the phase uncertainties in most realistic optical
interferometers. Here we propose and experimentally demonstrate a weak
measurement scheme to considerably suppress the phase uncertainties by the
direct amplification of phase shift in optical interferometry. Given an initial
ultra-small phase shift between orthogonal polarization states, we observe the
phase amplification effect with a factor of 388. Our weak measurement scheme
provides a practical approach to significantly improve the interferometric
phase resolution, which is favorable for precision measurement applications.
