When it comes to quantum technology, computing dominates the headlines around the world. Computers that use the laws of quantum mechanics are significantly faster for several classes of problems than even the most powerful supercomputers.
Quantum Imaging doubles the resolution of the microscope
But behind the scenes, other quantum technologies are emerging with the potential to revolutionize other areas of science. One such technology is quantum imaging, which uses the quantum properties of photons to enhance images.
Now Lihong Wang and colleagues at Caltech Pasadena have unveiled a quantum microscope that produces images with twice the resolution of conventional microscopes.
Crossing the border/ resolution of the microscope
Conventional imaging systems are limited in various ways by the properties of light. For example, the resolution of any image is limited by the wavelength of the light and the size of the aperture of the lens collecting the light. At the edge of the lens, the aperture diffracts or bends the light, causing it to interfere and create light and dark rings around every detail in the image. This ultimately limits what can and cannot be allowed.
Over the years, physicists have found various ways to achieve “super-resolution”, such as making lenses out of exotic substances called metamaterials, although this only works at short distances from the object.
Quantum mechanics offers another solution with entangled photons. These are particles of light that are separated in space but share the same existence. Wang and colleagues say these photons travel along symmetrical paths of equal length and then recombine. When this happens, “they behave like a single photon of half the wavelength, resulting in a two-fold improvement in resolution.”
This allows any stray photons at the original wavelength to be easily ignored, which also improves the image.
The trick, of course, is to construct an optical setup with exactly these properties, which has been achieved by Wang and co. They call their technique “quantum microscopy by chance.”
Their quantum microscope generates pairs of entangled photons and sends them down different paths. It turns out that only one of the photons needs to make contact with the object to be imaged. So one path goes through the object while the other goes through a reference plane.
The photons are then recombined in the detection plane, where they are captured by a sensitive photodetector. The process is repeated thousands of times to create an image, which currently takes about 15 minutes per image.
Carbon fibers imaged with classical and quantum coincidence microscopy (Source: arxiv.org/abs/2303.04948)
Nevertheless, the results are impressive. Wang and co have used the technique to image test targets, carbon fibers and even cancer cells. “With low-intensity illumination, we have shown that coincident quantum microscopy is suitable for non-destructive bioimaging at the cellular level, revealing details that cannot be resolved by its classical counterpart,” they say
Further improvements are theoretically possible. Quantum physicists predict that by entangling N photons it should be possible to improve the resolution by a factor of N. This will take a bit longer to achieve.
Reference: Quantum Microscopy of Cancer Cells at the Heisenberg Limit: arxiv.org/abs/2303.04948