Quantum interaction: 10,000 times faster than light

imagesizerBy Jesse Emspak

How fast do quantum interactions happen? Faster than light, 10,000 times faster.

That’s what a team of physicists led by Juan Yin at the University of Science and Technology of China in Shanghai found in an experiment involving entangled photons, or photons that remain intimately connected, even when separated by vast distances.They wanted to see what would happen if you tried assigning a speed to what Einstein called “spooky action at a distance.”

They didn’t find anything unexpected, but that wasn’t the point: in physics, sometimes it’s good to be sure. The group published their work on the ArXiv.org, a preprint server for physics papers.

Quantum physicists have long known that after two particles — photons, for example — interact, they sometimes become “entangled.” This kind of experiment has been repeated many times, and involves taking two entangled photons and sending them to different places. Perhaps photon A goes to Los Angeles and photon B goes to Boston.

When photon A is observed, it has a certain polarization, perhaps “up.” The other photon in Boston is always in the opposite polarization, “down.” No matter what measurement is made of photon A, photon B will always be opposite. It is impossible to tell what the polarization will be before you measure it, but the entangled photons always seem to “know” the right state to be in, instantaneously.

As Chad Orzel, assistant professor of physics at Union College, explained, “It’s as though you sent two cards to two different addresses. One might be the jack of diamonds and the other the ace of hearts. When you get the card at one address you know which one went to the other. Quantum mechanics is weird because until you open the envelope, saying which card it is doesn’t have any meaning; it could be either one.”

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