How to See Quantum Entanglement
2010-06-03 0:00

By Lisa Grossman | Wired.com


Human eyes can detect the spooky phenomenon of quantum entanglement — but only sometimes, a new study on the physics preprint website arXiv.org claims. While eyes can help determine if two individual photons were recently entangled, they can’t tell if the brighter bunch of photons that actually hit the retina are in this bizarre quantum state.

“In general you think these quantum phenomena that involve only a few particles, they’re really far removed from us. That is actually not so true anymore,” said physicist Nicolas Brunner of the University of Bristol. “You could really go to an experiment by just having people look at these photons, and from there really actually see entanglement.”

In an earlier paper, Brunner and colleagues at the University of Geneva in Switzerland sketched out an experiment in which a human observer could replace a standard quantum detector. This isn’t as far-fetched as it sounds, they say, because the eye’s most important job is to be a sensitive photon detector.

The researchers would first prepare two entangled photons — photons whose quantum properties are so intimately linked that one always knows what the other is doing. When an aspect of one photon’s quantum state is measured, the other photon changes in response, even when the two photons are separated by large distances.

The researchers would send one photon to a standard detector and the other to a human observer in a dark room. The human would see a dim point of light in either the right or left field of view, depending on the photon’s quantum state. If those flashes of light correlate strongly enough with the output of the ordinary photon detector, then the scientists can conclude that the photons are entangled.

“This is a standard way of measuring and detecting entanglement,” says physicist Nicolas Gisin of the University of Geneva, a coauthor of the new paper.


There’s just one problem: Humans can’t see individual photons. The retina needs at least seven photons to hit it at once before it sends signals to the brain. Also, 90 percent of photons are lost or scattered on the way through the gelatinous part of the eye to the retina. These restrictions mean that you need a lot of photons — at least hundreds, preferably thousands — to make a practical human quantum detector.

In 2008 a group in Rome found a way to clone an entangled photon that preserves the entanglement. If you treat the big bunch of clones as a single quantum state, the entire bunch is entangled with the other original photon, the researchers claimed.

“It’s like having a Schrodinger’s cat,” says Brunner, referring to Erwin Schrodinger’s famous 1935 thought experiment in which a cat in a box has a 50-50 chance of living or dying depending on whether a radioactive atom decays. In this case, the microscopic state of the atom is entangled with the macroscopic state of the cat: Either the atom decays and the cat is dead, or the atom doesn’t decay and the cat is alive. Until someone opens the box, the only way to describe the system is by including both the atom and the cat.

Gisin and colleagues thought this photon-cloning method would be perfect for their human quantum-detector experiments. All they would have to do is make a few thousand copies of one member of the original entangled photon pair, and send all those copies to the human observer.

But because entanglement is easy to break, the team was unsure if the photons that reach the observer’s eyes would still be entangled with the other photon.

To test this idea, Gisin and colleagues imagined what would happen if instead of cloning the original photon, they made the equivalent of a photocopy. Like a black-and-white Xerox of a color picture, some information about the original photon would be lost. Because the copied photons were never entangled with the original, they would still not be entangled when they reached the observer’s eyes.

The researchers compared the theoretical results using photocopied photons and a real quantum cloner, and found that they looked exactly the same. The human observer would see the same thing, even when the bunch of photons were just Xeroxes that couldn’t possibly be entangled with the other photon.

The group concluded that human eyes can’t see quantum entanglement between a macro-state and a micro-state. Schrodinger’s cat may well be entangled with the atom, but a human detector can’t tell.

But the human eye can reliably tell whether the original two photons were entangled. That’s still “seeing” entanglement, the authors say.

“Macro-micro is almost out of the question. But the micro-micro is nice as well,” said study coauthor Christoph Simon of the University of Calgary in Canada. “You’re bringing the observer a little bit closer to the quantum physics.”

The researchers are now working on ways to perform the experiment in the lab and expect it to be ready within two years.

“The theoretical paper is certainly sound and of good quality,” comments physicist Dirk Bouwmeester of the University of California, Santa Barbara.

But Gisin acknowledges that replacing quantum detectors with eyeballs would not lead to any new applications.

“Why do we do it nevertheless?” he says. “We find entanglement fascinating.”

Article from: Wired.com



Related Articles
Synchromusicology, Chromotherapy, Synesthesia, and the Aural Current of Electric Audiomancy (Video)
Russian Kirlian Camera can see Human Soul
Researchers Achieve Quantum Teleportation Over 10 Miles of Empty Space
The quantum computer in your head
Golden Ratio Discovered in Quantum World: Hidden Symmetry Observed for the First Time in Solid State Matter
Quantum Communication (Video)
Quantum Knowledge & Mind Over Matter (Video)


Latest News from our Front Page

Pressure from the United Patriots Front Stops Mosque Plan
2016-04-28 20:10
Pressure from the United Patriots Front appears to have killed off a mosque development in Narre Warren North. The City of Casey council now looks likely to withhold planning approval for the development in a special meeting set for Tuesday night. A council report, to be considered by councillors on Tuesday, recommends that the approval be blocked. The mosque opponents’ cause has been helped by councillor ...
Police face questions over the influence of the Freemasons
2016-04-28 20:48
South Yorkshire Police today face questions over whether powerful 'secret society' the Freemasons held sway over the force at the time of Hillsborough. Families of victims say that officers who were Masons were promoted into powerful positions despite being ill-equipped, including match commander David Duckenfield. Duckenfield told the fresh inquests he had been a Freemason since 1975 and became head of his ...
England Bans its Own Flag to Avoid Offending Muslims
2016-04-27 2:23
St. George's Cross "racist" towards immigrants Government officials said their city was ‘too multicultural’ to celebrate St George’s Day, England’s version of the 4th of July. The council said that displaying the English flag may have been seen as “racist” towards immigrants.
Half of Western European men descended from one Bronze Age ‘king’
2016-04-27 2:09
Half of Western European men are descended from one Bronze Age ‘king’ who sired a dynasty of elite nobles which spread throughout Europe, a new study has shown. The monarch, who lived around 4,000 years ago, is likely to have been one of the earliest chieftains to take power in the continent. He was part of a new order which emerged in ...
"Local Residents" Are Filmed Stealing Dozens of Bottles of Water at London Marathon Stop
2016-04-25 23:10
Editor's Comment: "Local" residents? Why bother blurring their faces? We know who they are. ... London marathon runners were robbed of dozens of bottled waters when thieves raided a refreshment area armed with trolleys during today's race. Nearby residents - including parents with children - were captured on camera piling up crates of free water handed out by volunteers during the 26-mile event. Marathon ...
More News »