From PhysOrg.com:

To get around that problem, the team, led by Jeff Lundeen, devised a method based on “weak” measurements, whereby an observation is made that only alters the particle just a little tiny bit and gives information about just one property of the particle at a time. Taking multiple such measurements of identical copies of a particle, such as a photon, gives more and more information, eventually approaching a very close approximation to the actual state of the system. In one respect this approach is similar to the way calculus is used to measure irregularly shaped objects by cutting it into a number that approaches infinity, virtual slices, then adding up the results. When combined with more certain “strong” measurement results, the procedure provides an accurate measurement of the wavefunction.