Quantum microscope can examine cells in unprecedented detail


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An artist’s impression of a quantum microscope

The University of Queensland

Powerful microscopes have made a quantum leap. Using a quantum trick with light has allowed researchers to examine living cells in unprecedented detail without destroying them, a technique that could improve medical diagnoses and microbiology research.

The microscopes that are generally used to examine living biological systems shine one or two bright lights on their targets, and more powerful light sources allow researchers to see the cells in greater detail. But this approach has a fundamental limit to the precision it can achieve: at some point, a bright enough light will destroy a living cell.

“Our understanding of life as it is now has relied almost entirely on the quality of our microscopes,” says Warwick Bowen at the University of Queensland in Australia. “We’re really limited by technology, and it’s not obvious how to break the existing limits because we’ve already pushed the intensity as high as we can without destroying the cell.”

Bowen and his colleagues have found a way to overcome this problem. They used a type of microscope with two laser light sources, but sent one of the beams through a specially designed crystal that “squeezes” the light. It does so by introducing quantum correlations in the photons – the particles of light in the laser beam.

The photons were coupled into correlated pairs, and any of them that had energies unlike the others were discarded instead of being paired off. That process lowered the intensity of the beam while decreasing its noise, which allowed for more precise imaging.

When the researchers tested their system, they found that they were able to make measurements that were 35 per cent sharper than a similar device that didn’t use squeezed light.

“In order to achieve this kind of measurement without quantum correlations, you’d have to turn the intensity up,” says Bowen. “But if you turned up the intensity enough to match these results, you’d destroy the sample, so we’re able to examine things that previously would have been impossible to see.”

These included the wall of a yeast cell (Saccharomyces cerevisiae), which is about 10 nanometres thick, as well as the fluid within a cell, both of which would be faint even with the best non-quantum microscopes, and completely invisible with standard microscopes. Observing these minuscule parts of living tissues could help us understand the basics of life at the smallest scales.

“This is a very exciting advance in the field of optical microscopy that opens the door for improving how state-of-the-art microscopes can work, at light intensities that are right at the threshold of damaging biological samples,” says Frank Vollmer at the University of Exeter in the UK.

Quantum microscopes will also have practical applications, Bowen says. For example, light-based microscopes are often used to determine if cells are cancerous or to diagnose other diseases, and squeezed light could significantly improve the sensitivity of those tests as well as speeding them up, he says.

Journal reference: Nature, DOI: 10.1038/s41586-021-03528-w

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