Physicists harness neglected properties of light

February 15, 2017
University of Toronto physics researchers Edwin (Weng Kian) Tham and Hugo Ferretti prepare to run a test in their quest to beat Rayleigh's Curse, by tapping into previously neglected properties of light. Credit: Diana Tyszko/University of Toronto

University of Toronto (U of T) researchers have demonstrated a way to increase the resolution of microscopes and telescopes beyond long-accepted limitations by tapping into previously neglected properties of light. The method allows observers to distinguish very small or distant objects that are so close together they normally meld into a single blur.

Telescopes and microscopes are great for observing lone subjects. Scientists can precisely detect and measure a single distant star. The longer they observe, the more refined their data becomes.

But objects like binary stars don't work the same way.

That's because even the best telescopes are subject to laws of physics that cause light to spread out or "diffract." A sharp pinpoint becomes an ever-so-slightly blurry dot. If two stars are so close together that their blurs overlap, no amount of observation can separate them out. Their individual information is irrevocably lost.

More than 100 years ago, British physicist John William Strutt - better known as Lord Rayleigh - established the minimum distance between objects necessary for a telescope to pick out each individually. The "Rayleigh Criterion" has stood as an inherent limitation of the field of optics ever since.

Telescopes, though, only register light's "intensity" or brightness. Light has other properties that now appear to allow one to circumvent the Rayleigh Criterion.

"To beat Rayleigh's curse, you have to do something clever," says Professor Aephraim Steinberg, a physicist at U of T's Centre for Quantum Information and Quantum Control, and Senior Fellow in the Quantum Information Science program at the Canadian Institute for Advanced Research. He's the lead author of a paper published today in the journal Physical Review Letters.

Some of these clever ideas were recognized with the 2014 Nobel Prize in Chemistry, notes Steinberg, but those methods all still rely on intensity only, limiting the situations in which they can be applied. "We measured another property of light called 'phase.' And phase gives you just as much information about sources that are very close together as it does those with large separations."

Light travels in waves, and all waves have a phase. Phase refers to the location of a wave's crests and troughs. Even when a pair of close-together light sources blurs into a single blob, information about their individual wave phases remains intact. You just have to know how to look for it. This realization was published by National University of Singapore researchers Mankei Tsang, Ranjith Nair, and Xiao-Ming Lu last year in Physical Review X, and Steinberg's and three other experimental groups immediately set about devising a variety of ways to put it into practice.

"We tried to come up with the simplest thing you could possibly do," Steinberg says. "To play with the phase, you have to slow a wave down, and light is actually easy to slow down."

His team, including PhD students Edwin (Weng Kian) Tham and Huge Ferretti, split test images in half. Light from each half passes through glass of a different thickness, which slows the waves for different amounts of time, changing their respective phases. When the beams recombine, they create distinct interference patterns that tell the researchers whether the original image contained one object or two - at resolutions well beyond the Rayleigh Criterion.

So far, Steinberg's team has tested the method only in artificial situations involving highly restrictive parameters.

"I want to be cautious - these are early stages," he says. "In our laboratory experiments, we knew we just had one spot or two, and we could assume they had the same intensity. That's not necessarily the case in the real world. But people are already taking these ideas and looking at what happens when you relax those assumptions."

The advance has potential applications both in observing the cosmos, and also in microscopy, where the method can be used to study bonded molecules and other tiny, tight-packed structures.

Regardless of how much phase measurements ultimately improve imaging resolution, Steinberg says the experiment's true value is in shaking up physicists' concept of "where information actually is."

Steinberg's "day job" is in quantum physics - this experiment was a departure for him. He says work in the quantum realm provided key philosophical insights about information itself that helped him beat Rayleigh's Curse.

"When we measure quantum states, you have something called the Uncertainty Principle, which says you can look at position or velocity, but not both. You have to choose what you measure. Now we're learning that imaging is more like quantum mechanics than we realized," he says. "When you only measure intensity, you've made a choice and you've thrown out information. What you learn depends on where you look."

Explore further: Quantum mechanics technique allows for pushing past 'Rayleigh's curse'

More information: "Beating Rayleigh's Curse by Imaging Using Phase Information" Physical Review Letters, journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.070801.

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Hyperfuzzy
1 / 5 (2) Feb 15, 2017
Well, each wavelet describes the motion of the charge; so, with accurate computer computation you will have an infinite resolution, albeit memory limited.
swordsman
not rated yet Feb 15, 2017
It's called "superposition". Not exactly new, but long neglected. The other important factor is that of the transverse properties of radiation. Also not new, but long abandoned. "Back to the Future" in reality.
antialias_physorg
5 / 5 (1) Feb 16, 2017
the experiment's true value is in shaking up physicists' concept of "where information actually is."

Information is wherever something changes (in a non-random way).

That said I'm not sure this will apply to observing stuff like binaries, as the phase isn't correlated with the source.
Alexander_IK
not rated yet Feb 17, 2017
Natural light sources observed through microscope or telescope are not coherent. It's not clear how phases in different parts of the image spots can tell something about structures of the sources. Splitting of whole image with beamsplitter and mixing its parts together will give no additional information.
RNP
5 / 5 (2) Feb 17, 2017
@Alexander_IK
Natural light sources observed through microscope or telescope are not coherent. It's not clear how phases in different parts of the image spots can tell something about structures of the sources. Splitting of whole image with beamsplitter and mixing its parts together will give no additional information.


Although I must confessing to not fully understanding it myself, the paper (here: https://arxiv.org...2666.pdf ) clearly states that this is not true, saying:

"In order to beat the diffraction limit for fixed, mutually incoherent sources, a paradigm shift arising from the realisation that there is a huge amount of information available in the phase discarded by IPC may prove revolutionary. "
Alexander_IK
not rated yet Feb 17, 2017
The paper contains too complicated description of the experiment. There is no full scheme of the experimental setup. Of course, a lot of information about a light source is coded in its phase (phases of photons). But there are two unsolved problems:
1. Separation and registration of phases of closest photons (light parts with uniform phase) for non-coherent source.
2. Knowledge about correlations between properties of the light source and phase characteristics of its photons. Special phase portraits of all the source parts are needed before measurements to resolute them using phase-image recognition.
Hyperfuzzy
not rated yet Feb 17, 2017
Heisenberg's uncertainty only applies to quantum systems, quantum systems do not exist; however, + and - charge exist as a combo, neutron; positive spherical field, proton; negative spherical field, electron. So I simply think of the world as a set of diametrical spherical fields. These fields are each a unique object, updated at the speed of light relative to its center. To obtain infinite precision throw out QM as simply non-causal and apply causality. The light, we call it light, is the wrinkles in the individual spherical fields, the information value, polarization, directional vector reflect the causal effects of the charges motion. Gravity is not a mirror, you need a media for that. By the way, the speed of light, know what you are talking about, yes its a constant; however you may measure any bubble as moving faster than light relative to you. juz say'n
RNP
5 / 5 (2) Feb 17, 2017
@Alexander_IK
But there are two unsolved problems:.................


What makes you think that these people, who are experts in their field, would have over looked these obvious considerations?

Is there something in the paper (I linked above) that you can identify to support your claim?
Alexander_IK
not rated yet Feb 17, 2017
I said nothing about the researchers- it is off topic. I found no solutions of these "obvious" problems in the paper. Do you see them?
RealityCheck
4.3 / 5 (6) Feb 17, 2017
Hi Forum. :)

It is apparent to any objective reader that the experimenters/claims are using "may be" etc etc 'aspirational' phrases which the unwary reader/believer could incorrectly take as substantive basis for 'expectations' engendered by such 'aspirational' personal hopes. The usual problem of 'artifacts' (from sloppy/inappropriate 'data selection' and data processing' etc) is still highly likely once the experimenters try it in real 'exercises' to tease out such info. The thing is not to get carried away with 'rose-colored glasses', when the problem is still very much SERIOUS, no matter what methodologies they employ when selecting/processing/interpreting what may be at root INSEPARABLE info which, although it must exist as such in the phenomena itself, may still be inaccessible to our methodologies/instruments and may mislead if not properly recognized as such during naive/simplistic exercises/modeling.

Good luck to them anyway! At least they are trying. Cheers. :)
Hyperfuzzy
not rated yet Feb 17, 2017
Hi Forum. :)

It is apparent to any objective reader that the experimenters/claims are using "may be" etc etc 'aspirational' phrases ...

Good luck to them anyway! At least they are trying. Cheers. :)

So, essentially, preliminary BS!
Da Schneib
5 / 5 (1) Feb 18, 2017
I'm not sure this will apply to observing stuff like binaries, as the phase isn't correlated with the source.
Sure it is. Phase is correlated with distance, and if there are two objects with different and changing distances, then their phases will move in and out of correlation, allowing the fact that there are two objects and not one to be detected well beyond the Rayleigh criterion over integration time. One could even determine their relative velocities from this information.

This is a very promising technique.
Alexander_IK
not rated yet Feb 18, 2017
"Phase is correlated with distance, and if there are two objects with different and changing distances, then their phases will move in and out of correlation, allowing the fact that there are two objects and not one to be detected well beyond the Rayleigh criterion over integration time."

Resolution of coherent sources using phase shift - may be. But for natural non-coherent sources this can't work.

Da Schneib
5 / 5 (1) Feb 18, 2017
They don't have to be coherent. The changes in phase will be evident from the differences in distance. The statistics ensure that.
Alexander_IK
not rated yet Feb 18, 2017
Or from distance between 2 spots on the surface of 1 non-coherent source? And how to measure phases of small light parts (photons) of investigated beam? Time of arriving photons to a detector is not the phase.
Da Schneib
5 / 5 (2) Feb 18, 2017
Meh, it seems to be working so far. Now we'll want to test it on a known but unresolved binary- that means on a pair of stars that are close enough to be under the Rayleigh criterion, but which show the typical variation in brightness of an eclipsing binary pair.

I expect they'll be doing that pretty soon.
smrtsmart
5 / 5 (2) Feb 21, 2017
Yes the sources are indeed incoherent, but the light does become more spatially coherent after it diffracts; check out the Van Cittert-Zernike theorem on wikipedia. This is why stellar interferometry works for example. The surprise here is that conventional imaging based on lenses and intensity measurement is not taking full advantage of this coherence.
Whydening Gyre
not rated yet Feb 21, 2017
Heisenberg's uncertainty only applies to quantum systems, quantum systems do not exist;

HF,
YOU are a quantum system. We ALL are. As a society we are a single quantum entity. And so on..
Anytime a complex system has potential for more than the single state of non-existant(doesn't matter it's "shape"), it's "quantum"...
Hyperfuzzy
not rated yet 18 hours ago
Heisenberg's uncertainty only applies to quantum systems, quantum systems do not exist;

HF,
YOU are a quantum system. We ALL are. As a society we are a single quantum entity. And so on..
Anytime a complex system has potential for more than the single state of non-existant(doesn't matter it's "shape"), it's "quantum"...

QM is not science, it's an aberration.
Alexander_IK
not rated yet 16 hours ago
Thanks to smrtsmart for clear explanation. It seems from the news story that the researchers are able to measure original phase of a light source. But they use induced partial coherence due to diffraction in the optical system and are able to register corresponding phase shifts only.

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