Quantum-Boosted Nonlinear Tunneling Driven by a Bright Squeezed Vacuum

Nonlinear processes, mediated by multiphoton interactions rather than single-photon response, drive numerous fundamental phenomena and momentous applications in modern physics. Among these processes, tunneling ionization plays a pivotal role as it drives high-harmonic generation, forming the basis of attosecond science and enabling the visualization and control of electron motion at its natural time scale. Quantum light, with its unique capacity for quantum noise redistribution, offers a transformative solution to boost nonlinear responses. Here, we report the first experiment of nonlinear tunneling ionization of the most fundamental system of atoms boosted by a quantum light - bright squeezed vacuum (BSV). Remarkably, the tunneling ionization of a single sodium atom induced by a 300 nJ BSV beam matches that achieved with a 7.1 {\textmu}J coherent light source, demonstrating a dramatic boost in nonlinear efficiency from phase-squeezed quantum light. Moreover, the effective intensity of the BSV light and thus the boosted tunneling ionization can be precisely controlled by tuning the degree of phase squeezing while maintaining the average pulse energy. These findings provide fundamental insights into quantum-boosted nonlinear effect and pave the way for efficient frequency conversion and quantum-controlled molecular reactions using tailored quantum light sources.