It is intuitively believed that the eigenvalues of a physical system and the corresponding spectral splitting of the output spectrum respond similarly to perturbations, for instance, both scale as $\sqrt{\epsilon }$ in the vicinity of a second-order exceptional point (${\text{EP}}_2$), where $\epsilon$ denotes the perturbation. Here we challenge this conventional view by demonstrating that the spectral splitting can be tuned to scale as $\sqrt[4]{\epsilon }$ or $\sqrt[6]{\epsilon }$ around an ${\text{EP}}_2$ in a nonlinear quantum system consisting of two coupled cavity squeezing processes. When measuring $\epsilon$ based on the spectral splitting, we further show that the corresponding measurement sensitivity can be enhanced by orders of magnitude below the standard quantum limit (SQL) owing to the combined effect of sublinear signal response and suppressed quantum noise. Our findings fundamentally reshape the understanding of the relation between the eigenvalues and spectral splitting in response to perturbations and also open alternative avenues for EP-based sensing with noise suppression below the SQL.

Close

PrevNext

View figure in article

• Cavity quantum electrodynamics
• Quantum fluctuations & noise
• Quantum sensing
• Squeezing of quantum noise