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

[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."
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