Scientists Just Solved a 30 Year Old Quantum Measurement Mystery

By Gizmodo Australia on at

The scientific community have been working on this one for more than 30 years. Australian scientists from Griffith University have worked out how to measure things with with single particles of light to a higher precision than ever before - on a quantum level.

But why does measuring things matter?

"Over the centuries advancements in how precisely we can measure things have consistently resulted in new breakthroughs in science and technology. So, we hope our result will be important for the future," said Professor Geoff Pryde from Griffith University's Centre of Quantum Dynamics.

Since the 80s scientists have been talking about a future where pairs of light beams, made up of a certain number of photons (that's the single particles of light), would be used to gain measurement information.

Here's how it would work, in a nutshell: the photons are entangled (or connected by quantum physics) between the two light beams. One beam would interact with the object being measured, and the other beam would be a reference.

The problem is that in this entangled quantum state, photons disappear. They can be absorbed or scattered in the very device they are working for.

This means until now, instead of sending out a search party, those missing photons had to be ignored. This meant it was impossible to compare the technique of measurement with just your standard light-based (but not quantum) one - not fairly, at least.

What Griffith University team have done to solve this problem is being hailed as a "breakthough".

They developed a low-loss photon source, and used it together with high efficiency detectors from the National Institute of Standards and Technology in the USA. And guess what? The chance of photons going missing was reduced to a level that meant photon quantum measurement techniques could reliably be used.

Just as the scientists of decades ago predicted.

So where to from here?

Making and using bigger entangled states, giving a bigger quantum advantage, is a focus for the photon measurement community now.

"Ultimately, the hope is that these quantum-enhanced measurements can be used to measure sensitive samples – such as quantum materials and biological systems – extracting the maximum information with the minimum damage to the sample," Professor Pryde says.

"We want to see how far this technology can be pushed." [Source]

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