Viewpoint article

See here for my Physics Viewpoint piece on a new experiment by Jeff Lundeen (Ottawa) and colleagues.

G. S. Thekkadath, L. Giner, Y. Chalich, M. J. Horton, J. Banker, and J. S. Lundeen, “Direct Measurement of the Density Matrix of a Quantum System,” Phys. Rev. Lett. 117, 120401 (2016).

Figure caption:

Standard quantum tomography maps out the quantum state of an object with repeated measurements of different physical observables to explore all independent degrees of freedom of the object. The procedure is similar to the reconstruction of the shape of the knight of a chess set by looking at its shadow from different directions. In the quantum case, each “snapshot” changes the state, disturbing it. Lundeen and colleagues’ experiment [1] is able to “weakly” measure the quantum object from several sides at once, without disturbing it, giving information about the whole.