Laser Creates Quantum Whirlpool

Quantus347 writes: Physicists at The Australian National Univ. (ANU) have engineered a spiral laser beam and used it to create a whirlpool of hybrid light-matter particles called polaritons. Polaritons are hybrid particles that have properties of both matter and light. The ability to control polariton flows in this way could aid the development of completely novel technology to link conventional electronics with new laser- and fiber-based technologies. Polaritons form in semiconductors when laser light interacts with electrons and holes (positively charged vacancies) so strongly that it is no longer possible to distinguish light from matter.

Comments

What, no Lightsaber jokes?

[Marxist Hacker 42]

Did I get first post?

Still, something tells me this is only a quantum effect, not macro

Re:What, no Lightsaber jokes?

[Anonymous Coward]

No, but I can't wait for the jokes about reversing the neutrality of the polariton flow.

I thought the distinction was arbitrary already

[i kan reed]

Polaritons form in semiconductors when laser light interacts with electrons and holes (positively charged vacancies) so strongly that it is no longer possible to distinguish light from matter.

I thought the distinctions made already are already mostly ones of convenience and scale: matter is slow and heavy enough to mostly be possible to model as point masses, while light is fast, light, and numerous enough to be more convenient to treat as non-discrete energy than as individual photons.

Re:I thought the distinction was arbitrary already

[students]

Matter has mass. Light has no mass. That's a pretty significant distinction. A polariton's mass can change continuously as a function of energy from zero to about twice the electron mass.

The summary is a little odd. A hole is not a charged vacancy. A vacancy typically refers to a fixed (at low temperatures) location where an atom is missing in the lattice of a crystal. A hole is a mobile positive charge with mass similar to the electron mass.

(Recently finished my PhD studying polaritons and vacancies.)

Re:I thought the distinction was arbitrary already

[Lord Crc]

The one scientists use today: invariant mass aka rest mass.

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html

Re:I thought the distinction was arbitrary already

[ThreeKelvin]

Currently, the known massless particles are gauge bosons, the photon (carrier of electromagnetism) and the gluon (carrier of the strong force). Massless particle.

Re:I thought the distinction was arbitrary already

[i kan reed]

If you actually click the photon link in that article, it lists a mass.

I feel like I'm going to argue semantics forever if I push this though.

Re:I thought the distinction was arbitrary already

[Khashishi]

Matter has mass, but not all that has mass is matter. There are several types of polaritons, and some of them are clearly not matter, even though they have mass. Phonon-electromagnetic wave quanta are clearly not matter. Moreover, you state that light has no mass, which normally I wouldn't disagree with, but in the context of polaritons, what about light propagating through nonlinear media? I think it's totally appropriate to say it is massive.

Re:I thought the distinction was arbitrary already

[students]

The rest mass is the right mass to talk about in nearly all situations, rather than the relativistic mass.

Re:I thought the distinction was arbitrary already

[Khashishi]

The term mass, without additional qualifications, means rest mass. Unusual definitions of mass ought to be clearly labeled, such as relativistic mass.

Re:I thought the distinction was arbitrary already

[iggymanz]

You are so busy being a pontificating numbnut you missed the sentence in the wikipedia article about relativistic mass

Re:I thought the distinction was arbitrary already

[Your.Master]

The question was:

Light absolutely has mass. For what definition of mass does a photon not have mass?

People have given very standard definitions for which a photon has no mass. Asked and answered.

The fact that relativistic mass is a thing is completely irrelevant to this discussion.

Re:I thought the distinction was arbitrary already

[Ceriel Nosforit]

More simply: light is massless but able to impart torque and momentum.

Convoluted literature like this seldom if ever mention a mechanism which makes this possible.

Re:I thought the distinction was arbitrary already

[Maritz]

Photons have zero rest mass.

Re:I thought the distinction was arbitrary already

[Maritz]

If a photon had rest mass, it would not travel at c (the speed of light). Neutrinos have a very small rest mass and travel close to c. If you research it, you'll find it is not semantics. These are technical terms with widely-accepted definitions.

Re:I thought the distinction was arbitrary already

[iggymanz]

Wrong, relativistic mass a very relevant point when talking of any "massless" particle that has real world consequences regarding momentum transfer, conservation of momentum etc. All "massless" particles must have relativistic mass, they cannot exist without it

Re:I thought the distinction was arbitrary already

[Bengie]

Matter has mass, but not all that has mass is matter

I'm not saying you're wrong, but I am having trouble finding a nice physics definition of "mass". All that I've found pretty much just says "mass is a property of matter".

Re:I thought the distinction was arbitrary already

[students]

Sure; this article is about exciton polaritons though.

You seem to be implying phonons are not matter. I would not call that "clear" at all. Maybe you should elaborate? Especially with respect to optical phonons.

Re:I thought the distinction was arbitrary already

[Khashishi]

Unfortunately, the term matter isn't universally agreed upon. Let's look at the definitions in wikipedia:
1. Does it have mass and volume (occupies space)? A phonon has mass, and maybe has volume, but doesn't 'occupy space' because it is a boson.
2. relativity, has rest mass? Phonons don't fit the equation E^2 = m^2 c^4 + p^2 c^2, because they have nonlinear dispersion equations, so it doesn't really make too much sense to talk about them at rest. They aren't Lorentz invariant, since they depend on the velocity of the material they are traveling through.
3. Is it made of atoms. Phonons are not made of atoms.
4. Is it made of electrons and baryons. no.
5. Is it made of quarks and leptons? No

Re:I thought the distinction was arbitrary already

[Khashishi]

There are two types of mass: inertial mass and gravitational mass. As far as we know, these two are equivalent.
Inertial mass is the resistance to motion (change in velocity). In Newtonian terms, F = ma. In special relativity, F = dp/dt = d(gamma*m*v)/dt
So, you can define mass as long as you can define a velocity and acceleration.

Gravitational mass is associated with gravity. In Newtonian physics, F = -G*m1*m2/r^2. In general relativity, gravitational mass is equivalent to rest energy. Gravity is given by Einstein's field equations which depend on the stress-energy tensor, which is a 4x4 matrix. The [0,0] element of the matrix is the rest energy density, which is the gravitational mass density/c^2.

Holodeck!!!!

[Anonymous Coward]

Holodeck anyone!!!!!

Re:Holodeck!!!!

[wonkey_monkey]

*plop* into a pile of bio-goo

People should clean it out after they've used it.

Re: I thought the distinction was arbitrary alread

[i kan reed]

Let's see here:

I thought the distinctions made already are already mostly ones of convenience and scale:

Independent clause introducing the rest of the post

Matter is slow and heavy enough to mostly be possible to model as point masses

Independent clause describing matter's characteristics

, while

Comma and conjunction to join two independent clauses

light is fast, light, and numerous enough to be more convenient to treat as non-discrete energy than as individual photons.

Independent clause describing the properties of light.

Which part went so far over your head?

Cliche Machine

[Tablizer]

Sharknado.....with quantum lasers on their heads!

(Sharknado III should actually do that. Some military experiment using armed sharks goes awry in the Quantum Whirlpool tank, and flying, zapping sharks are everywhere. Sure it's silly, but so was Sharknado I.)

Re:Cliche Machine

[geekoid]

Nice geocities link.

Re:Cliche Machine

[Tablizer]

It actually worked a year ago. They didn't shut down paying accounts until recently.

Re: I thought the distinction was arbitrary alread

[just_another_sean]

Made perfect sense to me. The Overrated moderation on the other hand doesn't make much sense considering his comment wasn't even rated yet.

Ignorance does not equal a new state

[ourlovecanlastforeve]

Just because you can't discern the difference between light and matter in this state -- this does not mean they are the same thing.

Re:Ignorance does not equal a new state

[Anonymous Coward]

Actually, didn't the article perfectly describe a photon?
http://physics.about.com/od/lightoptics/f/photon.htm

Re:Ignorance does not equal a new state

[michelcolman]

Just because you can't discern the difference between light and matter in this state -- this does not mean they are the same thing.

Exactly, if you just move to a different state that has different laws, and maybe even a different definition of pi, you'll find that it's perfectly legal to discern between light and matter.

Re: I thought the distinction was arbitrary alread

[sexconker]

It's i kan reed.
Just skip over it.

Re: I thought the distinction was arbitrary alread

[ArcadeMan]

Have you seen his name?

Re: I thought the distinction was arbitrary alread

[Artifakt]

Then the mod system was abused by somebody who either doesn't understand what simple English means or deliberately chose to misuse their tiny, trivial amount of power, probably because they have such a lack of a real life that they actually get an ego boost from it. Why are you sticking up for that?

Re: I thought the distinction was arbitrary alread

[sexconker]

U mad, i kan reed?

Re: I thought the distinction was arbitrary alread

[sexconker]

Nope, why would I be mad that you quoted your own dumbass post?

Almost there.

[DiegoMartinez]

I'm glad it isn't named the Australian National University of Science.

Re: I thought the distinction was arbitrary alread

[Maritz]

You certainly kan..!