Quantum fields in disequilibrium: Squeezed states

A spacetime description of squeezed states in quantum fields is presented, revealing the connection between squeezing and nonequilibrium dynamics. Squeezings in configuration space, occupation number space, and phase space are distinguished; generating transformations and criteria for their physical realization are discussed. The results have an immediate applicability to atoms and ions in traps, as well as to quantum optics in relativistic and nonequilibrium systems. Squeezing, sub-Poissonian statistics, and antibunching are all shown to be a direct consequence of spacetime inhomogeneities in the quantum field. The finite speed of communication between separate regions of the field (finite speed of light) places a lower limit on the attainable spectral width of squeezed states. The squeezing parameter for field quadratures has the appearance of a chemical potential in an inhomogeneous field, and through a renormalization may be generated by a Chern-Simons-like term.