  We propose a new method to directly measure a general multi-particle quantum
wave function, a single matrix element in a multi-particle density matrix, by
quantum teleportation. The density matrix element is embedded in a virtual
logical qubit and is nondestructively teleported to a single physical qubit for
readout. We experimentally implement this method to directly measure the
wavefunction of a photonic mixed quantum state beyond a single photon using a
single observable for the first time. Our method also provides an exponential
advantage over the standard quantum state tomography in measurement complexity
to fully characterize a sparse multi-particle quantum state.
