Squeezing and over-squeezing of triphotons

Quantum measurement: taken to the limit Quantum measurements are subject to an uncertainty that is usually distributed equally between pairs of complementary properties (such as position and momentum). However, a technique known as 'squeezing' can be used to reduce the uncertainty of one desired property at the expense of increasing that of the other. Optical spin-squeezed systems so far constructed are still many orders of magnitude away from achieving the maximum possible squeeze as determined by the Heisenberg limit. Now Shalm et al. demonstrate how an optical system can be squeezed almost all the way to that limit. They do this by overlapping three photons in an optical fibre and manipulating their spin to produce a composite particle, the 'triphoton'. Such states may offer important quantum advantages for high-precision measurement, lithography and information processing.