An Introduction to Squeezed States

Abstract

The in- and out-of-phase quadrature components of an oscillator amplitude have, even at zero temperature, an irreducible product of fluctuations as imposed by quantum mechanics and the Heisenberg uncertainty relation. Thus even ideal lasers operating in pure-mode coherent states exhibit amplitude and phase fluctuations, which, as we shall see, have an equal magnitude for any pair of in- and out-of-phase components. Squeezed states, which represent newly observed states of the radiation field,¹ possess fluctuations in either the amplitude or phase (but not both!) that are smaller than that offered by any ideal laser or even by the vacuum itself. This special property of squeezed states should lead to improved channel capacity in communications and to improved phase sensitivity in interferometers, just two of potentially many promising applications.²