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

By Lisa Grossman |

Human eyes can detect the spooky phenomenon of quantum entanglement ó but only sometimes, a new study on the physics preprint website claims. While eyes can help determine if two individual photons were recently entangled, they canít tell if the brighter bunch of photons that actually hit the retina are in this bizarre quantum state.

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

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 isnít as far-fetched as it sounds, they say, because the eyeís most important job is to be a sensitive photon detector.

The researchers would first prepare two entangled photons ó photons whose quantum properties are so intimately linked that one always knows what the other is doing. When an aspect of one photonís 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 photonís 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.

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

Thereís just one problem: Humans canít 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 ó at least hundreds, preferably thousands ó 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.

ďItís like having a Schrodingerís cat,Ē says Brunner, referring to Erwin Schrodingerís 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 doesnít 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 observerís 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 observerís 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 couldnít possibly be entangled with the other photon.

The group concluded that human eyes canít see quantum entanglement between a macro-state and a micro-state. Schrodingerís cat may well be entangled with the atom, but a human detector canít tell.

But the human eye can reliably tell whether the original two photons were entangled. Thatís still ďseeingĒ entanglement, the authors say.

ďMacro-micro is almost out of the question. But the micro-micro is nice as well,Ē said study coauthor Christoph Simon of the University of Calgary in Canada. ďYouíre bringing the observer a little bit closer to the quantum physics.Ē

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

ďThe theoretical paper is certainly sound and of good quality,Ē 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.

ďWhy do we do it nevertheless?Ē he says. ďWe find entanglement fascinating.Ē

Article from:

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

Professor: Reason Itself Is A White Male Construct
2015-07-04 3:55
A philosophy and religion professor at Syracuse University gave an interview to The New York Times Thursday in which he critiqued the notion of pure reason as simply being a “white male Euro-Christian construction.” Prof. John Caputo was being interviewed by fellow philosophy professor George Yancy for the 13th installment of an interview series Yancy conducts with philosophers regarding racial topics. Given its emphasis on first principles ...
The Broken Window Fallacy
2015-07-04 3:48
Youtube description: This short video explains one of the most persistent economic fallacies of our day. Source:
Jenji Kohan and the Jewish Hyper-Sexualization of Western Culture
2015-07-04 3:33
As detailed in The Culture of Critique, Freud and his followers regarded anti-Semitism was a universal pathology which had its roots in sexual repression. The theoretical basis for this can be found in Freud’s Three Essays on the Theory of Sexuality where he linked aggression to the frustration of human drives — especially the sex drive. Kevin MacDonald notes that: ...
Confederate History - Dispelling the Myths
2015-07-03 3:28
History books, the media, the school systems, etc abound in falsehoods and inaccuracies of Confederate and Southern history. This fact sheet will help to clarify and dispell some of these rampant inaccuracies. MYTH - The War of 1861 - 1865 was fought over slavery. FACT - Terribly untrue. The North fought the war over money. Plain ...
Gays Rights May Open Door for Pedophile Rights
2015-07-03 3:31
Democrats have attempted to normalize pedophilia as a sexual orientation. A recent Supreme Court ruling on same-sex marriage may soon allow pedophiles to argue they are suffering discrimination. ‚ÄúUsing the same tactics used by ‚Äėgay‚Äô rights activists, pedophiles have begun to seek similar status arguing their desire for children is a sexual orientation no different than heterosexual or homosexuals,‚ÄĚ writes Jack Minor ...
More News »