Amplitude-squeezed light is light with an intensity noise level below the shot noise level, i.e. below the standard quantum limit. That reduced intensity noise can be obtained only at the expense of increased phase noise. In a phase space representation (see Figure 1), the uncertainty region becomes squeezed in the sense that it becomes narrower in the amplitude direction and wider in the phase direction. This is one form of squeezed states of light.
Amplitude-squeezed light can be generated in different ways. One possibility is to drive a laser diode, held at a cryogenic temperature, with a very quiet electric current [4, 7], and typically also to operate it at a very low temperature. In other cases, optical nonlinearities are exploited. For example, amplitude-squeezed light can be generated in a doubly resonant [5, 6] or singly resonant  frequency doubler.
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