RESEARCHERS TURN UP EVIDENCE OF "SPOOKY" QUANTUM BEHAVIOR
By Gautam Naik, The Wall Street Journal, May 5, 2009
One of quantum physics' crazier notions is that two particles seem to communicate with each other instantly, even when they're billions of miles apart. Albert Einstein, arguing that nothing travels faster than light, dismissed this as impossible "spooky action at a distance."
The "great" man may have been wrong. A series of recent mind-bending laboratory experiments has given scientists an unprecedented peek behind the quantum veil, confirming that this realm is as mysterious as imagined.
Some key developments around one of quantum physics' weirdest notions: that two particles can affect each other even when they are billions of miles apart.
Quantum physics is the study of the very small -- atoms, photons and other particles. Unlike the cause-and-effect of our everyday physical world, subatomic particles defy common sense and behave in wacky ways. That includes the fact that a photon, which is a particle of light, exists in a haze of multiple behaviors. They spin in many ways, such as "up" or "down," at the same time. Even trickier, it's only when you take a peek -- by measuring it -- that the photon fixes into a particular state of spin.
Stranger still is entanglement. When two photons get "entangled" they behave like a joint entity. Even when they're miles apart, if the spin of one particle is changed, the spin of the other instantly changes, too. This direct influence of one object on another distant one is called non-locality.
These peculiar properties have already been proven in a lab and tapped to improve data encryption. They could also one day be used to build much faster computers. Some philosophers see quantum phenomena as a sign of far greater unknown forces at work and it bolsters their view that a spiritual dimension exists.
"We don't know how nature manages to produce spooky behavior," says Nicolas Gisin, a scientist at Geneva University, who led a recent experiment demonstrating action-at-a-distance. "But it's a fascinating time for physics because it can be mastered and exploited."
Einstein refused to believe that a photon could be in all states at once and set out to find an explanation for their seemingly odd behavior. God doesn't play dice with the universe, he said at the time. Danish physicist Neils Bohr, a big proponent of quantum uncertainty, shot back: "Quit telling God what to do."
Trying to poke holes in the notion of spooky action at a distance, Einstein and two colleagues published a paper in 1935 that appeared to demonstrate the existence of mysterious "hidden variables" and show that quantum theory was incomplete. In a seminal 1964 paper, Irish physicist John Bell raised questions about the mathematical validity of Einstein's work.
In a 1981 paper, Mr. Bell took a swing at Einstein's notion of "hidden variables" by relating the sock-wearing patterns of his physicist colleague Reinhold Bertlmann. Mr. Bell noted that if he saw one of Mr. Bertlmann's feet coming around the corner and it had a pink sock, he would instantly know, without seeing the other foot, that the second sock wouldn't be pink. To the casual observer that may seem magical, or controlled by "hidden variables," but it was no mystery to Mr. Bell because he knew that Mr. Bertlmann liked to wear mismatched socks.
Quantum particles behave a lot more oddly, and, thanks to Mr. Bell's work, experiment after experiment has shown that to be true.
Last year, Dr. Gisin and colleagues at Geneva University described how they had entangled a pair of photons in their lab. They then fired them, along fiber-optic cables of exactly equal length, to two Swiss villages some 11 miles apart.
During the journey, when one photon switched to a slightly higher energy level, its twin instantly switched to a slightly lower one. But the sum of the energies stayed constant, proving that the photons remained entangled.
More important, the team couldn't detect any time difference in the changes. "If there was any communication, it would have to have been at least 10,000 times the speed of light," says Dr. Gisin. "Because this is such an unlikely speed, the conclusion is there couldn't have been communication and so there is non-locality."
Other scientists have gotten a more direct look at the particles' secret behavior. They pulled off this feat by resolving something called Hardy's paradox, which basically addressed one of the trickiest aspects of quantum physics: by observing a particle you might affect its property.
In 1990, the English physicist Lucien Hardy devised a thought experiment. The common view was that when a particle met its antiparticle, the pair destroyed each other in an explosion. But Mr. Hardy noted that in some cases when the particles' interaction wasn't observed, they wouldn't annihilate each other. The paradox: Because the interaction had to remain unseen, it couldn't be confirmed.
In a striking achievement, scientists from Osaka University have resolved the paradox. They used extremely weak measurements -- the equivalent of a sidelong glance, as it were -- that didn't disturb the photons' state. By doing the experiment multiple times and pooling those weak measurements, they got enough good data to show that the particles didn't annihilate. The conclusion: When the particles weren't observed, they behaved differently.
In a paper published in the New Journal of Physics in March, the Japanese team acknowledged that their result was "preposterous." Yet, they noted, it "gives us new insights into the spooky nature of quantum mechanics." A team from the University of Toronto published similar results in January.
Some researchers are using the uncertain state of photons to solve real-world problems. When encrypting sensitive data such as a bank transfer, both the sending party and the receiving party must have the same key. The sender needs the key to hide the message and the receiver to reveal it. Since it isn't always practical to exchange keys in person, the key must be sent electronically, too. This means the key (and the messages) may be intercepted and read by an eavesdropper.
An electronic key is usually written in the computer binary code of "ones" and "zeros." Quantum physics permits a more sophisticated approach. The same "ones" and "zeros" can now be encoded by using the properties of photons, like spin. If someone intercepts a photon-based message, the spins change. The receiver then knows the key has been compromised.
MagiQ Technologies Inc. of Cambridge, Mass., refreshes its quantum keys as often as 100 times a second during a transmission, making it extremely hard to break. It sells its technology to banks and companies. Dr. Gisin is a founder of ID Quantique SA in Switzerland. The company's similar encryption tool is used by online lottery and poker firms to safely communicate winning numbers and winning hands. Votes cast in a recent Swiss federal election were sent in a similar way.
Because of its bizarre implications, quantum theory has been used to investigate everything from free will and the paranormal to the enigma of consciousness. Several serious physicists have devoted their lives to the study of such ideas, including Bernard d'Espagnat. In March, the 87-year-old Frenchman won the prestigious $1.5 million Templeton Prize for years of work affirming "life's spiritual dimension."
Based on quantum behavior, Dr. d'Espagnat's big idea is that science can only probe so far into what is real, and there's a "veiled reality" that will always elude us.
Many scientists disagree. While Dr. d'Espagnat concedes that he can't prove his theory, he argues that it's about the notion of mystery. "The emotions you get from listening to Mozart," he says, "are like the faint glimpses of ultimate reality we get" from quantum experiments. "I claim nothing more."