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Generation of few-cycle squeezed light

In aperiodically poled quasi-phase-matching (QPM) crystals, parametric down-conversion (PDC) can generate very broadband pulsed squeezed light. This is because each part of the crystal will generate squeezed light at a different frequency [1]. But the emission will be thus inhomogeneously broadened, and one requires special measures to eliminate the chirp accompanying the pulses. This can be done by placing a group-velocity dispersion material after the crystal [2] or by specially designing the nonlinear grating [3]. If the bandwidth of squeezed light is large enough, the squeezing and photon-number correlations, after the chirp is removed, will be “single-cycle”, with the correlation time comparable to one optical cycle [4].