Compact squeezed light source for higher-order Hermite–Gaussian modes

Squeezed light is a fundamental nonclassical resource in quantum optics, and considerable progress has been made in its generation and manipulation. Here, we experimentally demonstrate a compact higher-order spatial modes squeezed light source, achieved by integrating second-harmonic generation and optical parametric oscillation within a single doubly resonant cavity. The HG_{2<i>m</i>,2<i>n</i>} pump field, which is essential for the generation of HG_{<i>m</i>,<i>n</i>} mode squeezed states, is produced via internal second-harmonic generation, substantially enhancing both the conversion efficiency and mode purity. With this configuration, we successfully generated squeezed vacuum states in the HG_0,0, HG_1,0, and HG_2,0 modes, achieving squeezing levels of -4.53 ± 0.26 dB, -3.68 ± 0.19 dB, and -2.58 ± 0.08 dB, respectively. This platform provides a viable pathway for scalable, multimode quantum state generation, with broad potential in quantum metrology and quantum communication.