Direct measurement of the quantum wavefunction

The wavefunction, describing both the wave-like and the particle-like nature of everything in the Universe, is central to quantum theory. Physicists usually learn about it indirectly in tomographic experiments that measure only some aspects of its behaviour. Now a team from Canada's Institute for National Measurement Standards has developed a new and gentle technique that makes it possible to observe the wavefunction directly. They demonstrate the approach by measuring the transverse spatial wavefunction of a single photon. The discovery that the wavefunction can be probed directly provides a tool that could prove useful in a wide range of fields, and raises questions bordering on the philosophical about what the wavefunction actually is.