Quantum correlations overcome the photodamage limits of light microscopy.

Light microscopy is a powerful tool to understand the microscopic structure and dynamics of living systems. However, state-of-the-art microscopes use high intensity lasers that cause photodamage, severely disturbing biological processes and functions, and compromising viability. This introduces hard limits on their performance, constraining both sensitivity and imaging speed. Quantum correlations between the photons used in the microscope have been predicted to provide the only means to overcome these limits. Here we demonstrate this, achieving signal-to-noise beyond the photodamage-free capacity of conventional microscopy in a custom-designed ultrahigh efficiency coherent Raman microscope. We use the microscope to image molecular bonds in the interior of a cell with both quantum-enhanced contrast and sub-micron resolution. This allows the observation of nanoscale biological structures that would otherwise be obscured. Coherent Raman microscopes are widely used due to their capacity for extremely selective biomolecular finger-printing in unlabelled specimens, but photodamage is a roadblock for many applications. By showing that this roadblock can be overcome, and achieving this in a state-of-the-art microscope, our work provides a new path forward, offering the prospect of order-of-magnitude improvements in both sensitivity and imaging speed.