© Lloyd1. Deep Freeze Pauses Light
2. On the tv show The Universe on 1/31/2013 on the H2 History channel, the episode title was Deep Freeze. Toward the end was mentioned these statements paraphrased, now on Youtube at http://www.youtube.com/watch?v=OjoW2kdQ8Q4 (at 36 min. mark) by Alex Filippenko, UC,Berkeley:
3. Luciana Walkowicz, Princeton U says The lowest temperature reached is half a nanoKelvin. At such temperatures atoms clump together and synchronize motions, all behaving the same way. These super cold substances can stop light in its tracks. We can stop a beam of light, or slow it down, play with it and release it again. You can stop light, turn it into an electrical signal, and then release it and turn it back into light, which has all kinds of applications in electronics.
4. ---
5. Earlier Method to Pause Light
6. http://science.nasa.gov/science-news/science-at-nasa/2002/2~
7. Researchers have trapped a laser pulse inside a glass chamber — and released it again intact.
8. Last year [2001?], physicists at Harvard University shined a laser beam into a glass cell filled with atomic vapors.
9. [] The laser pulse was kilometers-long before it entered the cell, yet the pulse fit intact within the centimeters-wide chamber.
10. This improbable feat — stopping light — was accomplished by two teams. One was led by Ron Walsworth, a physicist at the Harvard-Smithsonian Center for Astrophysics, and the other by Lene Hau of Harvard University's Department of Physics. Walsworth's group used warm rubidium vapors to pause their laser beam; Hau's group used a super-cold sodium gas to do the same thing.
11. Below [image]: Before she managed to stop light altogether, Lene Hau and colleagues first slowed it to bicycle speeds in 1999.
12. Photons — that is, particles of light — are [thought to be] massless, and that's why they can travel so fast.
13. The Harvard researchers stopped their laser beams by "weighing the photons down."
14. >>>[LK: According to Mathis, they increased the photon mass by adding stacked spins to them.]
15. The technique requires two lasers: a "control laser" and a "signal laser." The signal laser is the one to be stopped. Using the control laser, Walsworth's team caused rubidium gas in the glass cell to become "dispersive" — in other words, the velocity of light passing through the gas depended sensitively on the color of the light. [] In such a dispersive gas, atoms and photons interact strongly, says Walsworth. "Effectively dragged down by strong interactions with atoms, the photons slowed to a crawl." Physicists call such an atom-photon system a "polariton."
16. >>>[LK: By Mathis' theory, the polariton is a photon to electron converter {like BC's iron planetars}.]
17. Next they reduced the intensity of the signal laser until the polariton was 100% atomic. There were no photons left inside the chamber. Yet the imprint of the photons remained — on the atoms themselves. Like a child's top, atoms spin. (Physicists say they "carry angular momentum.") Information describing the fading laser pulse was stored, like a code, in the up-and-down patterns of the atoms' spin axes.
18. [see caption]
19. Above [image]: As the laser pulse enters the chamber containing the rubidium vapor, the information that defines the light becomes imprinted on the atoms' spin states (indicated by the small arrows). In the moment that the light is "stopped," only the spin states exist. This image by Tony Phillips is based on another from the American Institute of Physics.
20. Freeing such a stored pulse is easy: another laser beam directed through the chamber can release it. "In the near future, this technique may enable efficient, reversible mapping of quantum information between light and atoms," says Walsworth.
21. [see caption]
22. The possibilities are mind-boggling: "Suppose you have some information encoded in atoms," says Walsworth. "You could map that information onto light, send it over to some other group of atoms, and imprint the information there." Walsworth calls this "quantum communication."
23. Computers do their work using binary numbers — that is, ones and zeros. Such "bits" are in constant motion inside your desktop PC. In a quantum computer the bits — called qubits — could be carried from place to place by photons. Horizontal polarization, for instance, might represent "0" and vertical polarization "1". (It doesn't end there: Qubits can be 0, 1, or a superposition of the two — it's allowed by quantum physics! Qubits are natural tools for "fuzzy logic." )
24. >>>[LK: Mathis found that QM is largely wrong, so fuzzy logic wouldn't work.]
25. Such a computer would work only if there were some way to stop light, change its state, and send it on its way again. Walsworth's team has demonstrated just such a sequence: While a light pulse was imprinted on the rubidium atoms, they made a simple change to the atoms' quantum states. Much to the researchers' delight, those changes were present in the regenerated light pulse.
26. [see caption] {Right [image]: Supercomputer; Roger Ressmeyer.}
27. Walsworth and Hau used vapors (rubidium and sodium) to pause light. Will the insides of quantum computers be vaporous as well?
28. Maybe not: A group led by Phillip Hemmer of Hanscom Air Force Base (he is now at Texas A&M University) has shown that light can be stopped as well by solids. They used a rare-earth doped insulator — a type of material generally used for ultra-high density optical memories and processors.
29. "It's very nice to think that it works in a solid state, which is moving more towards the electronics that we're familiar with," Walsworth says.