orbital angular momentum data transfer controversy

On a sunny day (Thu, 08 Nov 2012 00:24:33 -0800) it happened Jamie M wrote in :

I think one thing that the quantum club always forgets is the Shannon limit. Quantum computahs are limited because of noise, probably the reason we have never seen one do anything useful. Here it seems (I have just read the critical paper referred to) they try the same thing, and likely will die in noise the same way.

I think one thing that the quantum club always forgets is the Shannon limit. Quantum computahs are limited because of noise, probably the reason we have never seen one do anything useful. Here it seems (I have just read the critical paper referred to) they try the same thing, and likely will die in noise the same way. Ken

it.

... > I think one thing that the quantum club always forgets is the Shannon lim

it.

Now what is this? Are Pantelje and Tucker alter egos of the same ...err.. personality?

Regards, Mikko

Abstract. We point out that the assumption that more than two spatially orthogonal farfield wave modes (the two polarization modes) can leave an antenna and propagate in free space violates the Second Law of Thermodynamics and is thus incorrect.

However the optical guys have demonstrated 16 QAM in free space, using

Steve

Apologies, a new internet SNAFU. Ken

The Shannon limit applies to a channel. Before you can apply the Shannon limit argument to show that some technique cannot provide an increase in the information carrying ability, you have to show that it does not create new channels, or if it does, that it does so at the expense of the carrying ability of the existing channel(s).

Sylvia.

Not sure that's topical. The (silly) english have vertical TV dipoles, but most have horizontal TV dipoles., which is a form of 'static' polarizations. Could a polarization be modulated? Consider a transmission dipole rotating at 1 Mhz, with that rate detected, a 2nd channel might rotate at 1.0001 Mhz though with each at an emission frequency that is equal. Ken

I'm not an expert at this, but doesn't the Shannon limit consider the bandwidth vs the signal to noise ratio? Your transmissions can modulate all they want. The question is what does this do to the transmitted power level? How do you rotate the carrier in two different ways at the same time in a single carrier? Using two carriers doesn't violet the Shannon limit since they would have twice the power total.

Rick

How about helical? Solves thermal twisting here in AZ just ducky. ...Jim Thompson

Hi,

I don't think OAM and polarization are the same things, ie. take for example a linear polarized source, in which the electric and magnetic fields always have the same 180degree phase offset. If you rotate that source (ie like rotating a flashlight axially) to give the light beam non-zero OAM, then the phase offset of the electric and magnetic fields will still be 180 degrees, ie. still linearly polarized.

cheers, Jamie

On a sunny day (Thu, 08 Nov 2012 16:42:16 -0500) it happened Spehro Pefhany wrote in :

It is even simpler, if somebody states 'infinite', that triggers 'analog' in me, and how accurate you can measure an analog level. This goes for QM where 'infinate number of superimposed states' in my view equals bullshit, and for this example too. See:

On a sunny day (Fri, 09 Nov 2012 11:07:01 +1100) it happened Sylvia Else wrote in :

So, if you dump 3 buckets of water in the river in different ways, do you get more channels? It is a word game.

No, but that doesn't mean that doing something entirely different in an entirely different scenario wouldn't create more channels.

It's not a word game. Before you can use the Shannon limit you have to identify a channel. You can change the theory and call what it applies to an X, but then you have to identify an X.

Sylvia.

limit.

limit.

Doubt it, i have seen them disagree as well.

?-)

Dead link.

You are infinitely inaccurate. Hell, you can't even spell the word.

Look into 16 APSK and 32 APSK.

Would it have even been possible 20 years ago?

limit.

You can modulate polarization, sure. It's been done since the invention of dirt (or at least Pockels cells, which are almost that old).

The gee whiz guys don't seem to have remembered the concept of a complete orthonormal basis set, which is something they drill into you as a physics undergrad (probably as an EE undergrad too, if you take any elective fields courses). There just aren't any missing modes for the twisty folks to exploit--the twisty ones are linear combinations of ordinary Gauss-Legendre beams. The thermodynamic argument is a b***h slap way of putting that. It'll leave a mark.

The quantum folks made an analogous same mistake in the early history of quantum optics--it was widely believed that light from two different lasers couldn't form interference fringes. The radio folks, e.g. Hanbury Brown, knew better, and the physicists eventually came into line after Twiss and HB published an appropriately mathematical paper on the subject.

Not as well-clothed as your average emperor.

Cheers

Phil Hobbs

"Can't form fringes" according to what speed film? :-)

It's amazing how different, and how identical, light and radio are. It's also amazing how some people forget those basic facts.

Tim

it.

It's hard to comment anything constructive without more specificly stated criticism. I think Shannon limit (whatever you specifically mean by that) is well known within QC community.

Noise reduction is the bread and butter of the whole field, (i.e. getting the Johnson noise so low that the Callen-Welton tail becomes dominant), so it's hard to understand what exactly you think the QC community is overlooking.

Regards, Mikko