FTL signaling via frustrated total internal reflection

[Qfwfq]

It’s a bit off the topic of this thread, which was more along the lines of the question of whether massive macroscopic stuff can travel faster than c

Actually, this thread has touched upon just about any manner in which the title could possibly be construed, Cherenkov, Bell... you name it!

[Jay-qu]

PS: if there are no objections, I’ll move discussion of N & S’s experiment to its own thread, linked to from this and other threads that reference it. It’s a bit off the topic of this thread, which was more along the lines of the question of whether massive macroscopic stuff can travel faster than c

 

I was unaware 'something' was specific to macroscopic objects :pirate:

 

In all seriousness I think a new thread would be a good idea, we havent heard the end of this experiment, not by a long shot :)

[LaurieAG]

Got any links, Laurie, or even handmade sketches?

 

PS: if there are no objections, I’ll move discussion of N & S’s experiment to its own thread, linked to from this and other threads that reference it. It’s a bit off the topic of this thread, which was more along the lines of the question of whether massive macroscopic stuff can travel faster than c

 

Hello CraigD,

 

The original link is Popular Science - Feature and it has the exact same diagram that appeared in the New Scientist article. I have no objections to a new thread.

 

One thing that the article doesn't go into is the amplitude of the microwave. Also, there is a great difference (in scale) between a microwave and a photon with respect to their interractions between atoms in the glass and air. It's surprising that they claim both work, but on the same angles?

[CraigD]

Moderation note: This thread contains discussion of Nimitz and Stahlhofen’s experiment, its details, underlying physics, and implications. It was created from posts in the thread 1937, because discussion specific to this experiment and effect was deemed a bit off the topic of that thread, which was more along the lines of the question of whether massive macroscopic stuff can travel faster than c.

[CraigD]

The original link is Popular Science - Feature and it has the exact same diagram that appeared in the New Scientist article.

This article is the best I’ve seen so far on N & S’s experiment – thanks, Laurie. :thumbs_up

 

Despite spanning several years, it appears to me that all of these articles are discussing essentially the same experiment.

 

I was gratified to see that Nimtz’s diagram of the experiment differed from the one I sketched in this post only in the inclusion of the Goos-Hänchen effect (or perhaps more correctly, the Imbert-Fedorov effect, as I don’t think the microwave beam involved was polarized), an optical effect known for a long time, but not until now by me :). Although an very interesting effect, I don’t think it’s critical to the FTL-like effect demonstrated by the N & S’s experiment, nor has an effect on the predicted or detected FTL signal travel time.

One thing that the article doesn't go into is the amplitude of the microwave.

I recall reading in one of the articles that the amplitude (strength) of the microwave beam was very low. I suspect that the detectors used – which could measure the arrival of a photon to within [math]5 \times 10^{-15} \, \mbox{s}[/math], were best suited to as near a single-photon signal as the emitter could generate.

 

As I’m sure everyone involved in this thread understands, but I think worth stating, despite their name, microwaves are no more or less wave or particle-like than visible light: both are “light”, consist of photons (particles) which, like all particles, exhibit wavelike behavior. Microwave photons have energies of roughly [math]10^{-5}[/math] to [math]10^{-3}[/math] eV, corresponding to wavelengths between about 1 to .01 meters, while visible light photons have energies around roughly 1 eV, corresponding to wavelengths between about [math]10^{-7}[/math] to [math]10^{-6}[/math] m. (source: wikipedia article “Electromagnetic radiation”)

Also, there is a great difference (in scale) between a microwave and a photon with respect to their interractions between atoms in the glass and air. It's surprising that they claim both work, but on the same angles?

From what I can tell, the critical phenomena, Total internal reflection, guarantees that if TIR occurs at a given angle at the interface between 2 media (the prism and air, in the N & S experiment) for a lower-frequency, lower-refracting photon, it will for a higher-frequency, higher-refracting one. So, if the setup works for microwaves, it is guaranteed to work for visible light.

 

What I’m most curious about, and have not yet found mentioned, is the ratio (gain) of tunneled to reflected photons, and the relationship between the wavelength of the light, the distance between the prisms, and this ratio.

[Qfwfq]

What I’m most curious about, and have not yet found mentioned, is the ratio (gain) of tunneled to reflected photons, and the relationship between the wavelength of the light, the distance between the prisms, and this ratio.

See the details about the evanescent wave.

[Jay-qu]

I read on a poster at uni yesterday about an experiment that managed to 'teleport' a photons polarisation state - I dont know if it has much to do with this, Ill try get some more info.

[DougF]

I found the article (I think that you are talking about) here.

Instant transport: achieving quantum teleportation in the laboratory Science News - Find Articles

Instant transport: achieving quantum teleportation in the laboratory

Science News' date=' Jan 17, 1998 by Ivars Peterson

With a glittery shudder, a figure vanishes from view. At the same instant, a perfect replica shimmers into existence at a distant locality.

 

In science fiction thrillers, teleportation provides a convenient shortcut across time and space. In the real world, teleporting a person, a mouse, or even a coffee mug remains very much a dream.

 

In 1993, however, Charles H. Bennett of the IBM Thomas J. Watson Research Center in Yorktown Heights, N.Y., and his collaborators proposed that, in principle, it should be possible to take advantage of certain quirks of quantum behavior to teleport a specific characteristic of a photon, electron, or other quantum particle, though not the particle itself. The process would accomplish the instantaneous transfer of the quantum state of one particle to another, which could be at the other end of a room or across the galaxy (SN: 4/10/93, p. 229). In effect, that quantum state could be thought of as a message.

Two groups now report having successfully teleported photon characteristics in the laboratory.

 

Dik Bouwmeester, Anton Zeilinger, and their coworkers at the University of Innsbruck in Austria described the feat in the Dec. 11, 1997 Nature. Francesco De Martini and his team at the University of Rome "La Sapienza" in Italy are slated to report their results in Physical Review Letters.

 

"The methods developed for this experiment will be of great importance, both for exploring the field of quantum communication and for future experiments on the foundations of quantum mechanics," the Innsbruck group remarks.

 

Indeed, teleportation of the quantum states of particles is likely to become an important tool in efforts to design, build, and operate quantum computers (SN: 1/14/95, p. 30) and quantum information systems, Bennett says.

 

Teleportation of a quantum state depends on a peculiar phenomenon known as entanglement. The idea is to create a pair of particles that, because of their common origin, remain part of a single quantum system.

 

For example, shining a photon of a particular wavelength into the right sort of crystal converts it into a pair of photons with a special relationship, and they are said to be entangled.

 

According to quantum theory, neither photon has a particular polarization, or electric field orientation, until it's measured at a detector. Such a measurement transforms a photon's polarization from a range of possibilities into a specific, randomly chosen value. Surprisingly, measuring one photon's polarization causes the other photon of the pair to acquire the opposite polarization at the same instant, no matter how far away it is.

 

In general, practically anything done to one particle immediately affects the other in a predictable way. The entanglement is quite delicate, however, and the particles must be kept isolated from their environments to preserve their relationship.

 

In the Innsbruck experiment, to teleport a quantum state, the sender used ultraviolet light to prepare an additional photon. Its polarization state constituted a message to be communicated.

 

The message photon was brought together with one of the photons of an entangled pair in an optical device known as a beam splitter. These two photons were now entangled. They were then measured jointly to determine the resulting polarization.

 

"We learned how to entangle independently created photons," Zeilinger says. "This opens up a whole new class of experiments not previously possible."

 

When the measurement was made, the second, remote photon of the original entangled pair also acquired a polarization. A beam splitter and detectors measured its state. In effect, the message photon's state was transferred to the remote photon without the two ever coming into contact, and the original copy of the message was destroyed.

 

The sender then used conventional means to report to the recipient how the detectors were set when they measured the joint polarization. This determined what sort of measurement to make on the remote photon in order to retrieve the original polarization state that constituted the message. Because of the need for this conventional communication, the information required to detect that state must travel at the speed of light or slower, even if the polarization state is transferred instantly.

 

A tricky part of the experiment was proving that an unknown quantum state had actually been teleported. That required careful synchronization of the several polarization detectors used in the experiment.

 

Instead of having a separate message photon as well as an entangled pair, De Martini and his coworkers used two aspects of each particle of the entangled pair--the polarization and direction of motion. "These enter in the theory just like two separate particles, and they can be used just as well to demonstrate teleportation," says Tony Sudbery of York University in England.

 

With the success of quantum teleportation using photons as vehicles, researchers are considering the possibility of trying other combinations of particles, including electrons, atoms, and ions. They can envision transferring a fragile quantum state from a short-lived particle to a more stable quantum system.

 

 

Page 1 of 3[/quote']

[CraigD]

Just to lay a gentle hand on the helm of the thread, I’ll point out, as was noted upthread, that the phenomena demonstrated by N & S’s frustrated total internal reflection experiment is unrelated to “quantum teleportation” and similar effects involving quantum entanglement.

 

In short, quantum teleportation – applications of what Einstein and others described as “spooky action at a distance” – involve producing pairs of (or, rarely, more) particles such that a measurement of an attribute (such as polarity) of one determines the possible values of another. The most naïve (not inherently a derogatory term in math and science) interpretation of this suggests that this “entanglement” can be used to transmit information instantaneously across any distance that such particles can be separated from one another while kept in a state of quantum coherence. Such a device is commonly called an ansible. A more detailed analysis (beyond of the scope of this post) leads essentially all physicists to conclude that such a device is impossible – while quantum teleportation is potentially very useful, in that it promises to make possible the construction of absolutely identical objects, all such schemes to date require a conventional, light speed or slower signal to work, so can’t be used for FTL communication.

 

The N&SFTIRE is an example of quantum tunneling, and entirely different phenomenon than quantum entanglement. Quantum tunneling involves a single particle “jumping” across a region of space where it’s existence is prohibited – in this case, the gap between a totally internally reflective refractive interface (a face of a glass prism) and another prism.

 

AFAIK, unlike in the case of the ansible, there exists no thorough, compelling explanation of why tunneling such as that measured in the N&SFTIRE cannot be used to send a signal faster than light speed (but not instantaneously) across a specific optical apparatus.

[Qfwfq]

...there exists no thorough, compelling explanation of why tunneling such as that measured in the N&SFTIRE cannot be used to send a signal faster than light speed (but not instantaneously) across a specific optical apparatus.

If it's possible to send it faster than c then it's also possible to send it instantaneously and also back in time, unless SR and Lorentz covariance are horribly wrong which I doubt. I would like to see a thorough, compelling explanation of why tunneling could be used to achieve such a feat.

[Erasmus00]

AFAIK, unlike in the case of the ansible, there exists no thorough, compelling explanation of why tunneling such as that measured in the N&SFTIRE cannot be used to send a signal faster than light speed (but not instantaneously) across a specific optical apparatus.

 

I think the reason you can't send a signal this way is that the tunneling process is random, not all the photons will tunnel. It seems to me this will likely destroy any signal you try to pass.

-Will

[Jay-qu]

I dont think its that easy to discount.. Im sure an protocol could be designed, such as sending enough photons with the one signal so that the probability becomes reasonable enough to assume transmission.

[Erasmus00]

I dont think its that easy to discount.. Im sure an protocol could be designed, such as sending enough photons with the one signal so that the probability becomes reasonable enough to assume transmission.

 

Each photon can only carry 1 bit at a time (either spin up or spin down). Hence, any information carrying signal will require many photons. Removing a random number of random bits from that signal will destroy any signal.

-Will

[Jay-qu]

But what Im saying is if you send say 1000 photons and the probablity of tunneling is just 1% then at least 10 photons should make it through. So sending 1000 photons with the same spin state as a single bit could be used to send a signal.

[CraigD]

AFAIK, unlike in the case of the ansible, there exists no thorough, compelling explanation of why tunneling such as that measured in the N&SFTIRE cannot be used to send a signal faster than light speed (but not instantaneously) across a specific optical apparatus.

I think the reason you can't send a signal this way is that the tunneling process is random, not all the photons will tunnel. It seems to me this will likely destroy any signal you try to pass.

I dont think its that easy to discount.. Im sure an protocol could be designed, such as sending enough photons with the one signal so that the probability becomes reasonable enough to assume transmission.

A single bit signal consisting of a large number of photons is adequate to exhibit a particular signal speed, can’t be destroyed by loss of fewer than nearly all of its photons, and requires the minimal “protocol” of simply detecting at least one photon.

 

I think we’re confusing the concepts of latency (distance / signal speed) and data rate (“throughput”). A signal can have a high speed, and thus a low latency, and at the same time a low data rate, or vice versa. For example, a distant supernova (suppose that such a single event requires 1 day to detect) has a signal speed of c, and a data rate of [math]10^{-5} \, \mbox{bit/s}[/math] (1 event in one day), while a Netflix DVD has a signal speed (supposing, as is my case, a mailing distance of about 20 km, mailing time (latency) of about 36 hours, and about 2 hours of movie in 4 GB on DVD) of about [math]2 \times 10^{-11} \, \mbox{c}[/math] and a data rate of [math]6 \times 10^5 \, \mbox{bits/s}[/math] (the wikipedia article “comparison of latency and throughput” discusses this at greater length).

Each photon can only carry 1 bit at a time (either spin up or spin down). Hence, any information carrying signal will require many photons. Removing a random number of random bits from that signal will destroy any signal.

This assumes that the signal must be of the maximum possible “density” of 1 bit per photon. Normally communication with photons (light, radio, etc) is much less dense – consider, for example, a 19th – 20th century ship to ship signal lamp, hand operated using Morse code. Such a signal can withstand the loss of many individual photons to random causes (fog, bugs on the lens, etc) without being destroyed. Such a signal is (at a very rough estimate) around 10^22 photons/bit. A modern photo-optic (ie: fiber optic) communication system typically requires a few hundred photons/bit, although systems requiring as few as 1 photon/bit exist (ie: those used for quantum encryption) and do use polarization to encode bits in single photons.

 

As with the previously described data rate, photon/bit ratios are unrelated to signal speed. Transmitting a single bit between a sender and receiver in less time that the distance between them divided by c qualifies a signal as “faster than light”, as I understand the usual meaning of the expression. N & S’s experiment appears to have demonstrated just such a signal – detection of a single or many photons from a precisely timed emission [math]2 \times 10^{-11} \pm 5 \times 10^{-12} \, \mbox{s}[/math] sooner than an ordinary light signal could do so.

 

:( PS: I must confess a personal, not-fully rational bias: I’m uncomfortable with the possibility of FTL signaling. My reason is that I’ve long counted on special relativity as a sort of “absolute limiter” on the amount of information that can exist in a given volume of space, a limit important to some of my “believe intuitively but can’t prove” suspicions about the ultimate nature of reality. That it can be, in principle, violated, “blasphemes” against this belief of mine. None the less, I still find myself without any compelling objection to the implications of N & S’s experiment. :shrug:

[Erasmus00]

I must confess a personal, not-fully rational bias: I’m uncomfortable with the possibility of FTL signaling. My reason is that I’ve long counted on special relativity as a sort of “absolute limiter” on the amount of information that can exist in a given volume of space, a limit important to some of my “believe intuitively but can’t prove” suspicions about the ultimate nature of reality. That it can be, in principle, violated, “blasphemes” against this belief of mine. None the less, I still find myself without any compelling objection to the implications of N & S’s experiment. :eek_big:

 

The thing is: quantum mechanics and special relativity are consistent. (and when put together yield quantum field theory, which the standard model is built on). Hence, quantum mechanics cannot create ftl signaling. Unfortunately, building models of tunneling is rather difficult, but I do want to sit down and try to understand this experiment when I have a bit of time.

-Will

[Qfwfq]

Certainly, I don't expect a proper analysis would reveal propagation faster than c but I don't see it as a matter of photons getting lost. It's a matter of analysing an incoming wave packet and seeing how its Fourier transform is altered by the exponential factor of the evanescent wave. Anyone up to doing the integrals?