Physicists show that superfluid light is possible

October 27, 2010 by Lisa Zyga, feature

These images show the difference between the superfluid regime (left) of light and the turbulent regime (right), which is above the critical velocity. Image credit: Leboeuf and Moulieras.
( -- Superfluidity – the phase of matter that enables a fluid to move up the sides of its container – has been known about since the 1930s. Since then, superfluidity has become a prime example of how quantum effects can become visible on the macroscopic scale under certain conditions. Although physicists have previously considered the possibility of superfluid light, their results have been inconclusive until now. In a new study, physicists from France have theoretically shown that superfluid motion of light is indeed possible, and have proposed an experiment to observe the phenomena.

In their study published in a recent issue of , Patricio Leboeuf and Simon Moulieras from the University Paris-Sud and CNRS explain that is the ability of a fluid to move with zero dissipation or viscosity. A fluid behaves like a superfluid only under a certain critical velocity; above this critical velocity, superfluidity disappears. Most commonly demonstrated in liquid helium, superfluidity occurs when the helium is cooled and some helium atoms have reached their lowest possible energy. At this point, these atoms' quantum wave functions begin to overlap so that they form a Bose-Einstein condensate, in which all the atoms behave as one large atom, and their quantum nature is manifested on the macroscopic scale.

Previously, investigations of the superfluid motion of have not revealed clear evidence of the existence of a superfluid critical velocity. Although some recent experiments have observed superfluidity related to light, these experiments did not use photons, but a composite particle, called a polariton, which is a mixture of a photon and an exciton.

In this study, Leboeuf and Moulieras have shown that a superfluid critical velocity does exist in a nonlinear medium. They explain how superfluid light can be observed in an array of waveguides. From a dynamical point of view, light propagating through a nonlinear medium is formally equivalent to a Bose gas of interacting massive particles. Light can travel straight along the waveguides in the longitudinal direction, or it can tunnel between adjacent guides in the transverse direction. The benefit of this set-up is that it allows the scientists to engineer different characteristics of the array and control the light's flow.

The physicists were specifically interested in what happens to a as it travels through the array at different velocities in the presence of a defect. If the light is scattered by the defect, it means dissipative processes have occurred. If the light pulse moves through the defect without changing its shape (i.e., without losing collectivity), there is no dissipation and the light has superfluid motion. Through their calculations, the physicists showed that, for certain low velocities, the transverse motion of light is superfluid with zero dissipation. When the velocity increases, dissipative processes occur that destroy the collectivity of the light's oscillations, and superfluidity breaks down.

In the future, the physicists plan to further investigate additional details of superfluid light, such as how it relates to an underlying quantum theory of light and how it is connected to Bose-Einstein condensation. They predict that superfluid motion is a general property of light that exists in a variety of scenarios, and is not limited to the waveguide array proposed here. Superfluid light could also have applications in light transport optimization.

“One straightforward implication is related to transport in the presence of noise,” Leboeuf said. “Such a noise is expected to be present generically, since any material has imperfections and impurities. The impurities are responsible for the scattering of light. In the superfluid regime, we expect a light pulse to be able to propagate through a noisy medium without being affected or scattered (perfect transmission).”

Leboeuf and Moulieras plan to perform their proposed experiment and are discussing the opportunity with experimental groups at the Laboratoire de Photonique et de Nanostructures (LPN) at Marcoussis, France. However, the scientists said that superfluid light is not likely to have any strange effect analogous to a superfluid flowing up a container.

“The most basic 'strange' quantum effect that light shows related to superfluidity is, as shown in our article, dissipationless motion,” Moulieras said. “Another, though more indirect or spectacular, effect is related to quantized vortices, which were observed in laser patterns propagating through nonlinear media. Concerning other possibilities, such as fluid motion up the walls of a container, they are related, for atoms, to the forces between these atoms and a substrate, and the balance between capillary, gravity and viscous forces. We do not see a straightforward application of these concepts to photons, and therefore do not expect them for light.”

Explore further: Flatland physics probes mysteries of superfluidity

More information: Patricio Leboeuf and Simon Moulieras. “Superfluid Motion of Light.” Physical Review Letters 105, 163904 (2010). DOI: 10.1103/PhysRevLett.105.163904


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2.8 / 5 (4) Oct 27, 2010
any real world applications???
1.2 / 5 (19) Oct 27, 2010
This is very basic research.. For example, string theory is more than forty years old and it still has no experimental confirmation, testable predictions the less - not saying about real world applications.. Anyway, the superfluid photons could find an application during laser cooling of bulk volumes of boson condensates or for detection of gravitational waves with using of squeezed light technology.

BTW Preprint is here
3 / 5 (2) Oct 27, 2010
This work supports some ideas that I have posted elsewhere on Phys Org. The arxiv paper (see preceding post, and thank you TDK) describes the basic ingredients: light pulses, an array of waveguides, and harmonic on site energy. Art Winfree's work on coupled oscillators shows that oscillations synchronize under certain conditions. In this case, the oscillatory motions of the light synchronize, as the ingredients listed above would suggest--all are connected to all. In my opinion, the same fundamental phenomenon--synchronized oscillations--underlies superfluidity and superconductivity, low temp and high. Winfree's work, done in the 1960's, was extended by Kuramoto soon after, and then further extended by Steven Strogatz (author of Sync)in the last 15 years. Winfree applied his concept mainly to biology; Strogatz then developed it further mathematically. It has not been applied to physics, although intellectually the origins trace back to Huygens and his pendulum clocks.
2.7 / 5 (7) Oct 28, 2010
This is very basic research.. For example, string theory is more than forty years old and it still has no experimental confirmation, testable prediictions......

That's because string theory (and any multi-dimensional theory) is full of crap. The idea about time being the 4th dimension is also misleading.
not rated yet Oct 28, 2010
A fluid behaves like a superfluid only under a certain critical velocity; above this critical velocity, superfluidity disappears

Velocity relative to what? The container? Or perhaps the ether? I'm guessing the container. Superfluidity is awesome, by the way.
5 / 5 (2) Oct 28, 2010
What is called velocity here is the transverse velocity. Actually the interesting dynamics is happening in transverse dimension, not in the propagation direction. That is why there is a harmonic "trap", so that the transverse speed of light can be controlled by the amplitude of oscillations : small amplitude -> small velocity -> superfluid. Whereas large amplitude -> large velocity -> turbulent/dissipative. That is clear watching at the picture.
1 / 5 (1) Oct 28, 2010
Good comment, Smoulerias. I agree. The authors refer to "coherent collective oscillation." Winfree would say coupled oscillation or synchronized oscillation. The math in this article should be compared to Winfree's math and the Steve Strogatz math (see his Cornell site)in various PRL articles in the last decade exploring Winfree's idea. The authors also mention a potential deep connection to BEC. Yes, there is, and it is the same as the connection between BEC and BCS: synchronized oscillations. Only the nature of the oscillations varies. Quantum motion, in Planck's terms, is a limit cycle oscillation. Winfree said LCO is virtually the only major precondition for the application of his theory, but he did not apply his idea to physics, so he did not think about quantum as another way to say LCO. Incidentally, the authors say their article uses a classical perspective. When they investigate further, this is the way to investigate with a quantum perspective.
1 / 5 (1) Oct 28, 2010
Sorry for my typo. Meant to say Smoulieras. Article and pictures are excellent.
1 / 5 (1) Oct 28, 2010

That's because string theory (and any multi-dimensional theory) is full of crap. The idea about time being the 4th dimension is also misleading.

Really string theory is full of crap? I don't think that you should be challenging all of the physicists that are working on that theory. Besides it is widely accepted as truth in the scientific community. And if the 4th dimension is false too, how do you explain how light travels through empty space?
1 / 5 (1) Oct 28, 2010
When oscillations synchronize, several things happen. They create some degree of coherence within the group of oscillations. Symmetries usually accompany the synchrony. And a third effect is that the synchrony of the oscillations usually dictates precise order of the oscillating units, in time and space. Take BCS: phonons are oscillations. They sync with electrons. The electrons then sync with each other to form Cooper pairs--paired in two ways: antisynchronously as to their orbits (osc 1), and antisynch as to the spins (osc 2). Or take pnictide superconductivity: the oscillations that synchronize are the electromagnetic waves. They form an extended S wave, which can be visualized as a basket weave or an invisible egg carton. The angles of the intersecting waves must be exactly right to create this effect, which is why the angles in the pnictide material must be just so. Related effects dictated by perfectly synced oscillations create the supers: conductivity, fluid, fluid light. Occam
1 / 5 (15) Oct 28, 2010
IMO the superfluidity is simply the result of high compression of particles, the formation of Cooper pairs is rather byproduct of this effect. For example the superconductivity doesn't exists for metals, where no mutual compression of charge carriers exists between orbitals (sodium). In similar way, the synchronized oscillations are rather consequence of compressed (squeezed) state of particles, rather then the reason for superconductivity.

The more interesting thing is, photons are behaving like real bulky particles - IMO this effect will disappear for microwave photons and for longer wavelength the photons will behave rather like tachyons with negative rest mass prone to squeezing.
not rated yet Oct 28, 2010
I would guess real world applications would be
- no light loss fibre optics?
1 / 5 (1) Oct 28, 2010
Coupling among oscillators can be attributed to several factors: frequency of oscillation, proximity of oscillators, orientation of the oscillations, and range of communication (meaning the ability of the oscillators to "talk" to each other and "listen" to each other).

Phases of matter and their transitions exhibit these ingredients--particularly temperature (which affects frequency and range of communication) and pressure (which affects proximity and range of communication). So yes, compression can help produce coupling effects.

I don't believe that high compression is the reason for any of the supers. BCS Cooper pairs, for example, are rather far apart. As a slightly different example, consider the new quantum phase transitions. These typically involve organizational effects introduced externally by lasers and magnetic apparatus. These provide the ingredients, such as proximity, orientation, range of communication. Then quantum fluctuations sync.
not rated yet Oct 28, 2010
this property of light will go great lengths to lubricate matter transport or reformation technologies, possibly elemental synthesis :)
not rated yet Oct 28, 2010
This article and these comments are completely over my head; I have no idea what you people are talking about!
not rated yet Oct 28, 2010
Well, you are Dummy
not rated yet Oct 30, 2010
Along the line of ShadowRam, would line broadening be suppressed when a photon is passing through an absorber?
Intuition also troubles me to consider the transmission/proability function of the escaping evanescent waves just exterior to the total internal reflection of the superfluid light. Might the function be modified?
1 / 5 (2) Oct 30, 2010
I personlly lend more credence to quantum loop theory at the moment which has actually created particles rather from its principles than string theory which has created nothing (so far).

Its easy to create an infinite amount of mathematical models explaining an infinite amount of possibilities. However at the end of the day if a theory CANNOT produce tangible results it remains useless.

String theory to this day remains a useless unproductive mathematical model.
1 / 5 (3) Oct 30, 2010
I believe people like Hawkings ranting on about multi-universe theorys is not helping.

It would be quite impossible to have a multiverse such that an infinite amount of universe occupied the same time and space.

Frankly because if that were so and you had each universes creating more like an infinite unix child process program youd run out of space pretty quick.

If everything was occupied by a single universe infinite times there would be no room for the universe to be created in the first place. No space...No energy for every universe.

If you assume that all energy is just transformed from one form to another ad infinitum then you have a finite amount of energy with which to start a universe. So there are a finite amount of universe.

I instead imagine space to be filled with multiple universes next to each other a spaceship could fly between them.
5 / 5 (1) Oct 31, 2010
That's because string theory (and any multi-dimensional theory) is full of crap. The idea about time being the 4th dimension is also misleading.

Great comment. So when will you be submitting your alternate theory to a peer reviewed journal so that other scientists can comment on your work? Seeing as how you've obviously figured the universe out?

Criticizing other's work without any justification or suggesting alternate idea's is just plain ignorant.
1 / 5 (1) Nov 01, 2010
The "coherent collective oscillation" to which the authors refer is more significant than their phrase implies. In my opinion, these are quantized oscillations--synchronized quantized oscillations, in fact. This is the same principle that governs the behavior of the supers, and BEC, and for that reason, this research is of much greater interest than may be immediately apparent. Figures 2 a and b in their paper are visible evidence of a principle that lies at the heart of superconductivity (all types), superfluidity (both types--fermion and boson), BEC, Bosenovas and other phenomena. Internally, within the matter in question, every unit is linked and synchronized to many neighbors. As a result, the units must behave as one, giving rise to the behaviors that fascinate us. In this case, I imagine that photons are the relevant unit.
not rated yet Nov 02, 2010
Does this mean that communications through a channel using superfluid light would not be subject to the Shannon limit?

If so, I wonder if this could be used for optical communication on or between CPU chips at greater rates than allowed by Shannon capacity limited electrical signaling.
1 / 5 (1) Nov 19, 2010
The authors also refer to "quantized vortices" near the end of the Phys Org article above. Bear in mind that quantized vortices also appear in superfluid helium, and cuprate superconductors. As to the cuprates, see Phil Anderson's "Personal History," on Arxiv (November 2010), his farewell report describing his views on cuprate superconductors after 25 years. The last several pages of the article discuss quantized vortices, which he sees as a critical feature. My point is that quantum oscillations are the only conceivable ingredient that is common to these phenomena. Art Winfree's theory of synchronized oscillations is the only conceivable ordering mechanism that might create the perfect order in each of these mesmerizing phenomena from the raw material of quantum oscillations. As I have said in several posts above, the superfluid light created by Leboeuf and Smoulieras will one day be seen as having illuminated all of these mysterious phenomena, and more.
1 / 5 (2) Nov 19, 2010
.. Hawkings ranting on about multi-universe theorys is not helping...
Multiverse is artificial construct. The quantum mechanics, classical physics and/or relativity models are such a multiverses: an arbitrary slices of 3D reality separated with some number of extradimensions each other.

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