  Measurement of quantum state wavefunction not only acts as a fundamental part
in quantum physics but also plays an important role in developing practical
quantum technologies. Conventional quantum state tomography has been widely
used to estimate quantum wavefunctions, which, however, requires huge
measurement resources exponentially growing with the dimension of state. The
recent weak-value-based quantum measurement circumvents this resources issue
but relies on an extra pointer space. Here, we propose and demonstrate a simple
and direct measurement strategy based on $\delta$-quench probe: By quenching
its complex probability amplitude one by one ($\delta$-quench) in the given
bases, we can directly obtain the quantum wavefunction by projecting the
quenched state onto a post-selection state. As compared to the conventional
approaches, it needs only one projection basis. We confirm its power by
experimentally measuring photonic complex temporal wavefunctions. This new
method is versatile and can find applications in quantum information science
and engineering.
