Generation of few-cycle squeezed light

Summary form only given. 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].In this work, the first results on such broadband squeezing are demonstrated. In the 5-mm-long aperiodically poled MgO:LiNbO3 crystal we use, the QPM grating period changes from 7.38 μm to 8.91 μm. With this device, we generated bright twin beams through collinear frequency-nondegenerate high-gain PDC. The phase chirp was eliminated through the design of the nonlinear grating. The frequency bandwidth was measured to be 17 THz, a factor of 15 larger than in a periodically poled crystal. The correlation time was measured using non-phase matched sum frequency generation from the signal and idler beams. The dependence of the sum frequency intensity on the time delay between the signal and idler beams is shown in Fig.1. Fine-resolution scanning (b) shows a narrow peak, demonstrating a correlation time of 90 fs. It can be further reduced by using more advanced grating designs.