Two particles can become entangled so completely that a change in one immediately affects the other, no matter how far away it is. Until now, scientists have assumed such a marriage would endure forever.
But in a paper published today in the journal Science, two physicists show that entangled particles can suddenly and irrevocably lose their connection, a phenomenon called Entanglement Sudden Death, or ESD.
"The degree of information entangled can disappear faster than the information itself," said Joseph Eberly, a physicist at the University of Rochester, who, along with Ting Yu, co-authored the paper. "It's completely non-classical physics."
Entanglement is one of the stranger products of quantum mechanics, the area of physics that allows objects to fall through tables and postulates that teleportation is possible.
There are a variety of ways to entangle particles, depending on what kind of particles you're working with.
Particles of light, called photons, for example, can be entangled by shining high-energy beams on beta barium borate crystals. A high-energy photon breaks down into two lower-energy photons that, for example, may spin in opposite directions. If the spin of one photon is known, the spin of the other can be deduced, no matter how far apart the two become.
As those entangled particles move through the environment, other particles and fields degrade the connection — but some ties remain, it has long been thought.
Eberly describes the previous model of entangled particle decay like radioactive half-life — the period of time over which half of a given radioactive material will decay into other elements. No matter how much time passes, there will still be at least a tiny speck of radioactive material there.
What works for radioactive material does not work for entangled particles, say Eberly and Yu. Instead of slow decay, there is a sudden and abrupt death. The two particles remain, but the link between them is destroyed.
"This is a feature that people did not expect," said Bei Lok Hu, a professor of physcis at the University of Maryland. Even stranger, said Hu, is that suddenly disentangled particles can just as suddenly be reborn.
For now, the concepts of ESD and entanglement rebirth are only useful to physicists. There are no current practical consumer applications for entanglement.
The hope, however, is that eventually entanglement will lead to breakthroughs in cryptography, computing, even teleportation. The emergence of ESD could be a problem for these fields; permanently losing entangled information while, say, beaming from one place to another, Star Trek-style, would be a big problem, say both Eberly and Hu.
"Entanglement has a life of its own, and in some situations you see particles die, and sometimes they never come back again." said Hu.