A quantum state in a system in which the product in the Heisenberg uncertainty principle takes the lowest possible value, i.e. the product δ‎x δ‎p, where δ‎x is the uncertainty in position and δ‎p is the uncertainty in momentum, is equal to h/(4π‎), where h is the Planck constant, rather than greater than h/(4π‎), with analogous results for the uncertainty principle for other pairs of variables. The concept of a squeezed state is used extensively in quantum optics and in precision measurements.