Quantum Holography

Buzz Skyline writes "Physicists succeed where psychics fail. Researchers from Boston University propose a quantum holography system that can construct 3d images of objects sealed in closed containers. Could it lead to quantum luggage scanners at the airport?"

Comments

Some info for those that don't know...

[Mustang Matt]

http://www.sciam.com/explorations/061796exploratio ns.html

http://users.ox.ac.uk/~jsw/Schroedinger.html

Link to the real thing.

[HughsOnFirst]

Here is a link to the
actual paper itself. It's a PDF file though

Damnit!

[nanojath]

Yeah yeah, it's all funny but it ticks me off that nobody is pointing out that The principle illustrated in Schroedingers "cat" thought experiment are NOT THE SAME as the Heisenberg Uncertainty Principle. In fact, it ticks me off that nobody knows what the Uncertainty Principle is really about and people constantly confuse it with the whole indeterminate quantum particle state and whether does in fact create quantum indeterminacy on the macro scale (if a tree falls in the forest...) issue. Heisenberg's Uncertainty Principle establishes a mathematically defined absolute uncertainty balanced between the momentum and position of a quantum scale particle. The corresponding thought experiment would be the gamma ray microscope.

Re:Schroedinger's Cat

[yesthatguy]

*Anything* which firmly establishes the state of the cat will collapse the wave function. If you burn the box in a crematorium, the cat is definitely dead -- no uncertainty. If you "see" into the box using a method other than opening it, then you know the result. There are many ways to collapse the metaphorical wave function, observing it is just the most direct way, and also relates most directly to the position of an electron, which can best be determined by observation, though not with the naked eye.

Re:Schroedinger's Cat

[Faramir]

This is a good question, and there have already been several good answers. However, I don't feel like they've really answered your question.

Far from destroying the uncertainty principal, the article indicates that one of the "spooky" things about quantum holography is, essentially, the exploitation of the uncertainty principle.

Now, as to direct observation and the uncertainty principle: perhaps these should be explained for the casual /.'ers out there.

The uncertainty principle says that we cannot know exactly both the position and momentum at the same time. Momentum is a combination of mass and velocity. Mass often remains constant, so sometimes this is stated as "position and velocity" instead. Now, I used the word "exactly", and I meant just that. We can have a good idea of both numbers, but the more exact one measurement is, the less exact the other measurement will be. Basically, think of it this way: if we take a probe, like the tip of a pencil, and move it around till we find exactly were a particle is, we'll find it. But we'll also hit it and change its momentum.

Now, all observations require some kind of probe, be it pencils, electrons, or photons (light). A related feature of quantum mechanics is that the equations we use to determine where a particle (or wave, they're the same thing at this level) is going (the famous Schrodinger equations) don't actually tell us where a particle is going--only where its likely to go. So we don't even know how to say where it is going to go. In fact, it is considered that a particle does not have just one specific path until the particle has been measured.

In our case, that measurement--that is, the observation of the photons--occurs at the wall of the chamber. And from this data, convoluted equations work backwards to figure out what the photons bounced off of.

Hope that helps...

Re:Faster than light communication

[SeanCier]

I don't have a reference for you, but I can say that no, quantum entanglement does not allow FTL communication. To do anything interesting, you need to communicate information about the observation you made on one of the particles. Imagine twins -- one male, one female. They go to the two poles; at the North pole, somebody looks at one, and *boom*, she's female and the other one is male -- instantly. The people at the South pole look a microsecond later, and see that their twin is male. Okay... so? The people at the North pole haven't transmitted any information, even if the action occurred *instantly*.

The article doesn't make it clear, but the measurement taken in the chamber must, I have to assume, be transmitted and used in constructing that second image (it doesn't just *happen*; you can't shine a beam of light, even entangled photons, and expect them to magically scatter off nothing. When the first entangled beam is measured, quantities of the second half are determined, but that doesn't make them scattered, since it was *possible* they were in that state already... it has to be possible, that's how quantum physics works). It sounds like the information would be used in a second beam interfering with the intangled beam, but I'm not certain from the article... but I can guarantee that information has to be used.

background information about holography

[tcc]

For those of you interrested in holography:

Holography basics (aimed at Highschool students level).

Books and information on Holography

Some more holography Theory>

Original article

[Vadim Makarov]

I'm surprised nobody put a link to the original article.

Abouraddy,A., Saleh,B., Sergienko,A., and Teich,M. Quantum holography (PDF, 169KB, 8pages), Optics Express, 9, 498-505 (2001).

Read the damn thing (if you can :-)), then discuss.

Re:Probes?!

[statusbar]

I like to explain it this way:

Take a .wav file of a sine wave and edit it with your favourite sound editor. Zoom in so you see 100 cycles. Measure the time 100 cycles takes. From that you can calculate the frequency of your sine wave. At what time did this event occur? Well, the event is spread out over time. So we don't know the accuracy of the timing of the event very well.

Now zoom in more so only 1/2 a waveform shows. Measure it. calculate the frequency. You now have more accuracy in the timing of the event, but less accuracy of the frequency.

Heisenberg's principle is NOT the confusing thing about physics - it is plain reality! The thing that really is the source of the confusion is that the energy of a particle is related to its frequency - Just like the time and frequency were related in my example.

*IANAP*

--jeff

Re:Faster than light communication

[Mr. Slippery]

If you change an entangled photon in any way, the other one instantly changes the same way.

It's more correct to say that if one entangled particle changes, the other changes too. But that only helps you do instantaneous communication if you can change an entangled particle in exactly the way you want. No one's figured out how to do that.

As far as we can tell at present, quantum nonlocality and "spooky action at a distace" exist, but cannot be made to transmit any information.

Looking at a paper I did about ten years ago, I found the following quote from Nick Herbert's Faster Than Light that summarizes the situation:

Eberhard's proof applies to the quantum patterns...[it] guarantees that large-scale quantum patterns will never be observed to be connected faster than light. Bell's theorem, on the other hand, applies to the individual quantum events themselves, and proves that these little quantum jumps must be connected faster than light...Bell's theorem can coexist with Eberhard's proof because they each refer to different aspects of a quantum measurement. Bell's theorem...can also exist with the COP rule forbidding all superluminal connections that can be used for signaling, because these Bell-mandated FTL jumps occur in an utterly random manner.