Physics + Math

10
Feb

Entangled Light Microscope Could Sharpen Focus for Biology Researchers

Is quantum mechanics actually useful? That’s a common question asked by physicists and non-physicists alike. After all, the information we glean from how particles interact isn’t yet a staple of everyday life.

Occasionally, though, scientists apply far-out theories to very real world problems. Take a recent discovery in Japan, where Takafumi Ono and fellow researchers at Hokkaido University have built the world’s first entanglement-enhanced microscope. Yes, you read correctly: this microscope operates on a quantum level.

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The new microscope uses a 405 nm laser—the same wavelength as a Blu-ray player's laser—which is similar to the blue-violet laser seen here, which has a wavelength of about 462 nm.

It could be a boon to anyone studying super small moving or living things. Currently, if scientists want to get a detailed view of a spore or a microbe, for example, they have to use an electron microscope, which in addition to being expensive, blasts the sample with such an intense beam that if it was living at the beginning of the observation, it probably won’t be in the end. Plus, many electron microscopes require the sample to be coated in a thin film of gold to enhance electron reflection. That pretty much rules out studying anything that moves or is alive, from complex proteins to single-celled protozoans.

But the entanglement-enhanced microscope doesn’t require samples to be immobile, nor does it bombard them with lethal beams. Rather, it uses an existing process, known as differential interference contrast microscopy, and gives it a boost by relying on the principle of entanglement. In differential interference contrast microscopy, an object is observed using two beams of photons, produced by splitting a single beam of light into two orthogonally polarized beams. These are focused on separate but adjacent spots, and the shape and texture of the object is detected when the two beams bounce back. When there’s no change, the two beams don’t interfere. But when one beam passes over a change before the other, the interference in returning photos is detected.

Measurements using this technique are good, but can be improved if the two photon beams are entangled. Entangled particles start off close together, exchanging intimate information about each other. Then when separated, they’re still able to communicate at a rate that’s seemingly instantaneous—faster than the speed of light. A microscope that uses entangled photons, then, would provide more information than a normal microscope can because each beam automatically provides information about the other.

MIT Tech Review reports:

Ono and co demonstrate this using entangled photons to image a flat glass plate with a Q-shaped pattern carved in relief on the surface. This pattern is just 17 nanometres higher than the rest of the plate and so tricky to resolve with ordinary optical techniques.

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Observations made by the entanglement-enhanced microscope (left) and a differential interference contrast microscope using classical light (right)

Entangled photons significantly improve on this. Ono and co say the signal to noise ratio using their technique is 1.35 times better than the standard quantum limit. And the resulting image is noticeably improved, simply by visual inspection (the image with entangled photons is on the left in the above figure). “An image of a Q shape carved in relief on the glass surface is obtained with better visibility than with a classical light source,” they say.

An entanglement-enhanced microscope wouldn’t be quite as high resolution as current electron microscopes, but the benefit of studying living organisms and cells or active, moving proteins could be more than worth loss of magnification for some researchers. That kind of improvement is what biologists have been waiting for. The revelations that could result from an entanglement-enhanced microscope, then, could be something of a macroscopic advance.

Learn more about the quantum realm in "Fabric of the Cosmos: Quantum Leap."