Efficient quadrature squeezing in a photonic crystal microresonator

Many emerging quantum technologies rely on squeezed states of light, in which noise in one field quadrature is reduced below the standard quantum limit at the expense of increased noise in the conjugate quadrature. Such states play an important role in quantum communication, computation, and sensing. In this work, we demonstrate single-mode quadrature squeezing via dual-pump spontaneous four-wave mixing in a nanophotonic microresonator fabricated from low-loss silicon nitride. The device employs a carefully engineered microresonator with a tailored nano-corrugation pattern that suppresses unwanted parasitic parametric processes that would otherwise degrade the squeezing performance. Using this approach, we achieve 7.8 dB of on-chip squeezing in the bus waveguide and identify clear pathways for further improvement. These results establish a promising route toward integrated squeezed-light sources for quantum-enhanced interferometry, Gaussian boson sampling, coherent Ising machines, and universal quantum computing.