Amazing, if true......could lead to quantum computing!

[Peter Lemkin]

Light stopped completely for a minute inside a crystal: The basis of quantum memory

• By Sebastian Anthony on July 25, 2013 at 6:49 am
  

Scientists at the University of Darmstadt in Germany have stopped light for one minute. For one whole minute, light, which is usually the fastest thing in the known universe and travels at 300 million meters per second, was stopped dead still inside a crystal. This effectively creates light memory, where the image being carried by the light is stored in crystals. Beyond being utterly cool, this breakthrough could lead to the creation of long-range quantum networks and perhaps, tantalizingly, this research might also give us some clues on accelerating light beyond the universal speed limit.
Back in 1999, scientists slowed light down to just 17 meters per second, and then two years later the same research group stopped light entirely but only for a few fractions of a second. Earlier this year, the Georgia Institute of Technology stopped light for 16 seconds and now, the University of Darmstadt has stopped light for a whole minute.
To stop light, the German researchers use a technique called electromagnetically induced transparency (EIT). They start with a cryogenically cooled opaque crystal of yttrium silicate doped with praseodymium. (The image above is unrelated; sadly there isn't an image of the actual crystal that was used to stop light.) A control laser is fired at the crystal, triggering a complex quantum-level reaction that turns it transparent. A second light source (the data/image source) is then beamed into the now-transparent crystal. The control laser is then turned off, turning the crystal opaque. Not only does this leave the light trapped inside, but the opacity means that the light inside can no longer bounce around the light, in a word, has been stopped. (Read: IBM creates first cheap, commercially viable, electronic-photonic integrated chip.)

With nowhere to go, the energy from the photons is picked up by atoms within the crystal, and the "data" carried by the photons is converted into atomic spin excitations. To get the light back out of the crystal, the control laser is turned back on, and the spin excitations are emitted at photons. These atomic spins can maintain coherence (data integrity) for around a minute, after which the light pulse/image fizzles. In essence, this entire setup allows the storage and retrieval of data from light memory (or should that be optical memory?)
In the image above, you can see that the scientists successfully stored a simple image (three horizontal lines) in the crystal for 60 seconds. It should be possible to store data for longer periods, too, using other crystals such as europium-doped yttrium silicate and by using specially tailored magnetic fields. (Read: The first quantum entanglement of photons through space and time.)
Light-based memory that preserves quantum coherence (such as polarization and entanglement) is vital for the creation of a long-range quantum network. Just as with conventional, electronic routers, quantum routers must be able to store incoming packets, and then retransmit them which is exactly what today's discovery allows. Even so, though, there are still a few barriers to overcome before we can roll out a quantum internet namely, we must find a method of coherently storing light that introduces so little noise that single photons can still be reliably stored/retrieved, and we need to do it at room temperature, too. Cryogenics might be acceptable at the data center level, but I can't imagine having a cryogenically cooled router in my house.

[Peter Lemkin]

The first quantum entanglement of photons through space and time

• By Sebastian Anthony on May 24, 2013 at 7:30 am
  
• 44 Comments
  

Ready for a mind-bending news story that will forever change your perception of life? Quantum physicists in Israel have successfully entangled two photons that don't exist at the same time. They create one photon and measure its polarization, destroying it they then create another photon, and though it never coexisted with the first, it always has the exact opposite polarization, proving they're entangled.
Don't worry if you have a little trouble trying to bend your head around this: Quantum mechanics, almost by definition, is completely different from our own perceptions and experiences, which are governed by classical mechanics. Believe it or not, quantum mechanics actually has no problem with the behavior demonstrated by the Israeli physicists entanglement was never a tangible, physical property, and this experiment is a perfect example of why it's sometimes very naive to boil quantum ideas into classical analogies.
Entanglement is a state where the state of two quantum particles (photons, for example) are intrinsically and absolutely linked. Quantum particles, due a principle called quantum superposition, exist in every theoretically possible state at the same time. A photon, for example, spins horizontally and vertically (different polarizations) at the same time. When you measure a quantum particle, though, it fixes on a single state. With entanglement, when you measure one half of the entangled pair, the other half instantly assumes the exact opposite state. If you measure one photon and it's vertically polarized, its entangled sibling will be horizontally polarized.
Quantum entanglement, between photons that never coexist [Image credit: Science]

As for how the Israelis entangled two photons that never coexist, the technique is rather complex. They start by producing two photons (1 & 2) and entangling them. The first photon (1) is immediately measured, destroying it and fixing the state of the second photon (2). Now a second pair of entangled photons (3 & 4) is created. They then use a technique called "projection measurement" to entangle 2 and 3 which, by association, entangles 1 and 4. Even though photons 1 and 4 never coexisted, they know the state of 4 is the exact opposite of 1.As we've covered before, entanglement seems to occur instantly, even if the particles are on opposite ends of the universe. This experiment shows how entanglement exists through time, as well as space or, in scientific terms, the non-locality of quantum mechanics in spacetime.
Does this experiment have any implications, beyond its use as a sublime example of the weirdness of quantum mechanics? As always with quantum entanglement, there is a possibility that "projection measurement" could be used in quantum networks. Instead of waiting for one half of the entangled pair to arrive at its destination (along a normal fiber optic network), this two-pair approach would allow the sender to manipulate his photon instantly. As Anton Zeilinger, a quantum physicist not involved with the study, tells Science: "This sort of thing opens up people's minds and suddenly somebody has an idea to use it in quantum computing or something."
Now read: Quantum entangled batteries could be the perfect power source

[Albert Rossi]

Pretty cool. I wonder what percentage efficiency would be necessary to make it viable.

As per quantum entanglement -- pretty spooky stuff. Bell's Theorem has to be one of the strangest results at the edges between quantum mechanics and relativity.

[Peter Lemkin]

Pretty cool. I wonder what percentage efficiency would be necessary to make it viable.

As per quantum entanglement -- pretty spooky stuff. Bell's Theorem has to be one of the strangest results at the edges between quantum mechanics and relativity.

This is IMO almost 'off the charts' into 'Star Trek' or Science Fiction territory. Stopping light?! Faster than light speed?! Quantum entanglement is very strange, indeed...and not easy for the layperson to understand. Once you understand it, it is even harder to believe. No one knows where this could lead or how long before it would be controllable by humans, if ever. My fear is always the military wanting to use it for evil, when it certainly offers almost magical pathways for good and the unimaginable positive....but that's not their 'gig'.

[Albert Rossi]

My fear is always the military wanting to use it for evil, when it certainly offers almost magical pathways for good and the unimaginable positive....but that's not their 'gig'.

You said it. Of course, the quantum computer is the NSA holy grail; RSA decryption would no longer be an NP-hard problem.