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From physnews@aip.org Tue Jan 27 15:31:03 1998 Date: Tue, 27 Jan 1998 08:46:26 -0500 From: physnews@aip.org (AIP listserver) Message-Id: <199801271346.IAA15741@aip.org> To: physnews-mailing@aip.org Subject: update.356
PHYSICS NEWS UPDATE The American Institute of Physics Bulletin of Physics News Number 356 January 27, 1998 by Phillip F. Schewe and Ben Stein LOCALIZATION OF LIGHT has been achieved by an Amsterdam- Florence collaboration (contact Ad Lagendijk, adlag@phys.uva.nl). Consider the movement of light through a diffuse medium such as milk, fog, or sugar. The light waves scatter repeatedly, and the transmission of light decreases as the light gets reflected. In the Amsterdam-Florence experiment something different happens. By using a gallium-arsenide powder with a very high index of refraction but with very low absorption at near infrared (wavelength of 1064 nm), the researchers were, in a sense, able to get the light to stand still. That is, the light waves get into the medium and bounce around in a standing wave pattern, without being absorbed. This is the first example of "Anderson localization" for near-visible light. This medium is not what would be called a "photonic bandgap" material (analogous to a semiconductor for electrons) but more like a "photonic insulator." (Wiersma et al., Nature, 18/25 December 1997; see also www.aip.org/physnews/graphics) QUANTUM EVAPORATION occurs in a new experiment when a beam of phonons (little pulses of sound issuing from a warm filament) inside a pool of superfluid helium-4 is aimed at the liquid surface from below. In analogy with the photoelectric effect (in which light ejects electrons from a surface), the phonons pop helium atoms up out of the liquid. By measuring the momenta of the phonons and the evaporated atoms, one can determine that the atoms originally had zero momentum parallel to the surface, demonstrating directly (for the first time) that the He-4 atoms had been part of a Bose-Einstein condensate (BEC), in which the atoms fall into a single quantum state. Theories of superfluid He-4 had supposed that the atoms reside in a BEC state, but this had not been experimentally verified until now. The researcher, Adrian Wyatt of the University of Exeter, believes this method can be used to generate beams of coherent helium atoms (an "atom laser" effect). (Nature, 1 January 1998.) ANOTHER VERSION OF QUANTUM TELEPORTATION is being published by researchers in Italy and England (Francesco DeMartini, University of Rome, demartini@axcasp.caspur.it). Like the Innsbruck teleportation scheme published several weeks earlier (Update 351), this demonstration employs a pair of entangled photons. Whereas the Innsbruck experiment teleported the polarization value of a third, distinct "message photon" to one of the entangled photons, the Rome scheme encodes one of the entangled photons with a specific polarization state and transmits this state to the other entangled photon. Although different from the Innsbruck experiment (which had a 25% teleportation success rate) and the original theoretical proposal for teleportation, this scheme works 100% of the time if the receiver applies the right transformations on the second photon. (D. Boschi et al., upcoming article in Physical Review Letters). In another, theoretical paper, Sam Braunstein of the University of Wales (Bangor) and Jeff Kimble of Caltech propose an experimental method for extending quantum teleportation from transmitting discrete variables such as polarization to transmitting continuous variables like the amplitude of the electric field associated with a light wave. (Braunstein et al., Phys. Rev. Lett., 26 January 1998.)
ANOTHER VERSION OF QUANTUM TELEPORTATION is being published by researchers in Italy and England (Francesco DeMartini, University of Rome, demartini@axcasp.caspur.it). Like the Innsbruck teleportation scheme published several weeks earlier (Update 351), this demonstration employs a pair of entangled photons. Whereas the Innsbruck experiment teleported the polarization value of a third, distinct "message photon" to one of the entangled photons, the Rome scheme encodes one of the entangled photons with a specific polarization state and transmits this state to the other entangled photon. Although different from the Innsbruck experiment (which had a 25% teleportation success rate) and the original theoretical proposal for teleportation, this scheme works 100% of the time if the receiver applies the right transformations on the second photon.
I wonder how far off use of this technique for interplanetary rovers might be (10 years, 20 years)? Remote (Earth) rover manipulation is tedious at best due to several minutes (or an hour or more to the outer planets) of propagation delay. Autonomous rovers need enough smarts built-in to handle unexpected situations, a non-trivial problem. An alternative is to establish a link using entangled photons. If a simple approach to saving these entangled states during signal transit, in both directions, were found instantaneous communication and simplified remote control would be a reality. Of course one needn't stop there. If entangled states could be stored for several years, instantaneous communication with neighbooring stars is a real possibility. Coupled with advances in mind-machine science it might someday be possible to explore, first-hand, our local portion of the galaxy without leaving earth, or upload/download one's consciouness to vessels in remote locations. Speaking of which, do the current SETI programs check for signal modulation using polarization. If we've discovered this trick, sure so have other intelligent life forms. Most natural sources of radiation tend to unpolarized, so a rapidly flucuating polar modularion might easily appear to be noise. --Steve
Steve Shear postulates:
Of course one needn't stop there. If entangled states could be stored for several years, instantaneous communication with neighbooring stars is a real possibility.
And in whose local Lorentz frame would such communication be "instantaneous"?
Coupled with advances in mind-machine science it might someday be possible to explore, first-hand, our local portion of the galaxy without leaving earth, or upload/download one's consciouness to vessels in remote locations.
Uh, no. The operators for corresponding observables at both ends of such an experiment commute, so it is not possible to transmit information non-locally using such an apparatus. This was discovered when the first experiments to verify the Einstein-Rosen-Podolsky effect were done. You need the results of measurements on the opposite end to decrypt the information at the end you are at. The Dancing Wu-Li Masters are closed for business. -- Eric Michael Cordian 0+ O:.T:.O:. Mathematical Munitions Division "Do What Thou Wilt Shall Be The Whole Of The Law"
This was discovered when the first experiments to verify the Einstein-Rosen-Podolsky effect were done. You need the results of measurements on the opposite end to decrypt the information at the end you are at.
I guess I'm over my head in such matters. From my, admitedly, shallow understanding of wave function collapse, etc., I was under the apparent misimpression that once collapsed (e.g., by Alice entangling a 'modulation' photon M (of a known polarization) with one member (photon A) of an entangled pair, one of which was sent to Alice and the other (photon B) which was sent to Bob, photon B's polarization state was determined and could not subsequently be altered by Bob's measurement with his receiver. Could you recommend a good article which explain this paradox to a non-quantum mechanic? --Steve
At 8:34 PM -0800 1/27/98, Tim May wrote:
At 7:56 PM -0800 1/27/98, Steve Schear wrote:
Of course one needn't stop there. If entangled states could be stored for several years, instantaneous communication with neighbooring stars is a real possibility. Coupled with advances in mind-machine science it might someday be possible to explore, first-hand, our local portion of the galaxy without leaving earth, or upload/download one's consciouness to vessels in remote locations.
Who's your supplier?
EPR Pharmaceuticals. Want their address? --Steve
At 7:56 PM -0800 1/27/98, Steve Schear wrote:
I wonder how far off use of this technique for interplanetary rovers might be (10 years, 20 years)? Remote (Earth) rover manipulation is tedious at best due to several minutes (or an hour or more to the outer planets) of propagation delay. Autonomous rovers need enough smarts built-in to handle unexpected situations, a non-trivial problem. An alternative is to establish a link using entangled photons. If a simple approach to saving these entangled states during signal transit, in both directions, were found instantaneous communication and simplified remote control would be a reality.
Nothing in quantum teleportation has been shown to propagate signals faster than light. (If you don't believe me, look into it. Start by reading the FTL discussions about Bell's Theorem.) I personally doubt that any flat spacetime topology (e.g., wormholes excepted) will admit any FTL signals. A lot of things would dramatically change if FTL communication existed...not the practical "communication" issues, which are human social minutiae, but issues about synchronization of reference frames and causality violations.
Of course one needn't stop there. If entangled states could be stored for several years, instantaneous communication with neighbooring stars is a real possibility. Coupled with advances in mind-machine science it might someday be possible to explore, first-hand, our local portion of the galaxy without leaving earth, or upload/download one's consciouness to vessels in remote locations.
Who's your supplier? --Tim May The Feds have shown their hand: they want a ban on domestic cryptography ---------:---------:---------:---------:---------:---------:---------:---- Timothy C. May | Crypto Anarchy: encryption, digital money, ComSec 3DES: 408-728-0152 | anonymous networks, digital pseudonyms, zero W.A.S.T.E.: Corralitos, CA | knowledge, reputations, information markets, Higher Power: 2^2,976,221 | black markets, collapse of governments. "National borders aren't even speed bumps on the information superhighway."
On 28 Jan 1998 12:24:30 -0600, Tim May <tcmay@got.net> wrote:
I personally doubt that any flat spacetime topology (e.g., wormholes excepted) will admit any FTL signals. A lot of things would dramatically change if FTL communication existed...not the practical "communication" issues, which are human social minutiae, but issues about synchronization of reference frames and causality violations.
I remember seeing on one of those science specials on The learning channel (or mabye the Discovery channel) that a professor did figure out (accidentally) how to send information faster than light. The only thing I remember about it was the the signal was some kind of music. I remember now, it was a special on time travel on a month ago. Anybody catch it? -- Phelix
Tim May wrote:
Nothing in quantum teleportation has been shown to propagate signals faster than light. (If you don't believe me, look into it. Start by reading the FTL discussions about Bell's Theorem.)
True, but there are some other interesting effects which could be explained by FTL communication, such as the fact that light diffracted through two slits shows an interference pattern, even though one of the slits is farther away than the light travel time from where the pattern appears. Then there's the fact that light appears to propegate faster in a region of space 'starved' of virtual particles by the casimir effect. That one is a favorite among warp drive theorists. :)
Phelix wrote:
I remember seeing on one of those science specials on The learning channel (or mabye the Discovery channel) that a professor did figure out (accidentally) how to send information faster than light. The only thing I remember about it was the the signal was some kind of music.
http://i02aix1.desy.de/~mpoessel/nimtzeng.html http://www.npl.washington.edu/AV/altvw75.html http://www.uni-koeln.de/~abb11/ http://www.aei-potsdam.mpg.de/~mpoessel/nimtzeng.html http://www.fringeware.com/msg/1996/msg00155.html
Phelix wrote:
I remember seeing on one of those science specials on The learning channel (or mabye the Discovery channel) that a professor did figure out (accidentally) how to send information faster than light. The only thing I remember about it was the the signal was some kind of music.
http://i02aix1.desy.de/~mpoessel/nimtzeng.html http://www.npl.washington.edu/AV/altvw75.html http://www.uni-koeln.de/~abb11/ http://www.aei-potsdam.mpg.de/~mpoessel/nimtzeng.html http://www.fringeware.com/msg/1996/msg00155.html
participants (6)
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Eric Cordian -
Jim Choate -
nobody＠REPLAY.COM -
phelix＠vallnet.com -
Steve Schear -
Tim May