LONG ARM: So-called high-NOON entangled states could someday find use in supremely sensitive interferometers, such as the LIGO gravity wave detector in Washington State.
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Quantum entanglement, a phenomenon by which two or more particles share correlated properties through some instantaneous link, is tricky business. The quantum-mechanical bond entangling two particles is so delicate, it can be broken by any number of outside perturbations. Try entangling three particles, and the system becomes just that much more vulnerable to interference.
Nevertheless, physicists strive to entangle ever larger systems, with the ultimate goal of harnessing quantum effects in large numbers of particles for computation, communication, or ultraprecise measurements. A paper in the May 14 issue of Science reports progress in that quest, in the form of an experimental setup that entangles five photons. The researchers, from the Weizmann Institute of Science in Rehovot, Israel, coaxed the photons into what is called a NOON state, in which the particles have two possible paths to choose from but collectively follow only one of them.
NOON is shorthand for the two possible states N0 and 0N, which signify that N photons follow one path, while zero photons follow the other. Until a measurement is made, the photons are said to be in a superposition of the two states. For large values of N, the states are cheekily dubbed "high-NOON" states, and five photons is the highest NOON yet.
Experimental physicist Itai Afek, a Weizmann graduate student and study co-author, explains that his group mixed light from two sources at a beam splitter to entangle the photons and separate the two paths. A beam splitter is essentially a mirror that reflects half the incident photons, allowing the other half to pass through unscathed. With properly entangled photons, however, the behavior is strongly correlated—whichever path the photons choose to follow, they do so en masse. "The five photons reach the beam splitter, and either all of them are reflected or all of them are transmitted, so they behave collectively," Afek says.
That correlated action could have benefits beyond clever quantum trickery. "These photons act collectively like one fat photon," Afek says, "and this fat photon has a wavelength that is N times smaller than the wavelength of the light we use." In other words, a five-photon NOON state has a wavelength just one-fifth the size of its entangled photons, which is a boon to precision measurements using optics. "Generally speaking, short wavelengths imply high resolution," Afek adds. One wavelength-dependent measurement approach is interferometry, in which interference between two beams of light can reveal subtle differences in the lengths of the paths the beams have traveled. Experiments are already under way using interferometric arms several kilometers long to try to detect ripples in spacetime known as gravity waves.
Entangled light, with its diminished wavelength, could even be used to etch ever smaller details onto electrical circuits using optical lithography, but that probably will not find its way into desktop computers anytime soon. "I should be honest—it has been discussed a lot, but there are many problems to actually applying it," Afek says. He adds that high-resolution microscopy is likely a more feasible application in the near term.
Although the Weizmann group has generated the largest NOON state yet, entangling five photons is not a record per se. In 2007, another group reported entangling six photons in a different kind of state. But Afek notes that in that work "the number of spatial modes is identical to the number of photons you are measuring"—in other words, there are not two paths the photons can follow, but six. "We're cramming all of the photons into one of two possible situations," Afek adds. "This makes it much more relevant to interferometry, because typically you have two arms. So it's convenient to have all of your photons in those two arms."
The researchers claim that their NOON state scales easily to accommodate more photons—on paper, at least. "As a theoretical scheme it works as well for 100 photons as for five," Afek says. But actually achieving large-scale entanglement in the lab is no picnic. "These fat photons, the fatter they get, the more sensitive they get—they get very touchy," he says. "The bigger they are, the more perfect your setup has to become to observe them."
Afek acknowledges that applications for entangled photons in NOON states appear to lie rather far in the future, but for now his group is content to tinker with one of the finickiest properties of physics. "What we're trying to do is scale up this behavior and see what the difficulties are when the system grows," Afek says. "When you want to get larger and larger states, you really have to meet the high standards that quantum mechanics sets for you."
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13 Comments
Add Commenti thought that the main idea for entanglement is to separate them a part so that one gives instant notification to a remote one...if they're all together what is the use.....
Reply | Report Abuse | Link to thisA smart thing to do with entanglement would be to look for it in starlight,by setting up a two slit experiment,if someone else is out there looking,and using a two slit experiment it would cause a wave function drop on this end,and by this means, instance communication with someone light years away could occur. Looking for a signal in radio waves could be fruitless search,and even if one is found it could take years if not centuries to return a message.Wherein if coherent wave function drop is found and the star is the same distance away from us as them we could begin a conversation right away.We our selves are now looking for Earth like planets around other stars,we can only assume that others out there are doing the same thing.If in fact we have been found by another species on a distant world they would be looking for stars the same distance away from them as we are.It could be this is already happening,we just haven't been looking for for entanglement in starlight.I suggest we do so,it is something we could do cheaply.In fact it could have been done ever since entanglement was discovered.
Reply | Report Abuse | Link to thisTo Wayne Williamson...if they're all together what is the use.....
Reply | Report Abuse | Link to thisOff the top of my head... display systems with seemingly infitate refresh rates for a start.
Wayne, read the rest of the article.
Reply | Report Abuse | Link to thisJohnay...just did(again and again)...and the point your trying to make is what...maybe the refined measurement ability???
Reply | Report Abuse | Link to thisscratch that...being able to "view" and measure at 10,100,1000,etc... times the normal resolution is a great advancement....(just not what i think of when i hear entanglement;-)
Could this technology be used to develop more sensitive neutrino,and dark energy detectors,and like I said seeking entanglement in starlight,and light from other Earth like planets in the search for life?I like the idea of using it to detect gravity waves.There may be other information hidden in the fluctuations of space-time as well.Who knows maybe it could used to study other subatomic particles like the quarks that make up all matter.Thus using direct measurement instead of particle colliders.
Reply | Report Abuse | Link to thisNow could you entangle 5 groups of 5 particles each to make a very fat photon blob? Then 5 x 5 x 5..?
Reply | Report Abuse | Link to thisOne fifth the wavelenth means a five times higher frequency. Does this mean the five correlated photons have five times the energy of five non-correlated photons. If so, could superposition be used to boost the power of the lasers at the National Ignition Facility? Or, are photons generated in lasers by definition correlated?
Reply | Report Abuse | Link to thisOne fifth the wavelength is five times greater frequency. Does this mean that five correlated photons have five times more energy than than five non-correlated photons? And, if so, could this magnification of power be used for projects like the National Ignition Facility at Lawrence Livermore?
Reply | Report Abuse | Link to thisthis entanglement is killing me-
Reply | Report Abuse | Link to thiswhere?
on, no?
no matter where; however, if so, what, when, how (superposition), and mostly Why?
I feel smart until I read articles on Quantum anything.
Reply | Report Abuse | Link to thisSearching favorable exoplanets for entangled wave function drop would be far better then massive plasma starlight, for finding an observor. How though would the alien know any better then us which photon is missing from their double slit experiment because we were looking at them? Could we use a small telescope at home and stand outside in the open, to discover an alien life form, or could we try it with a microscope and see if a bugs eye observor catches our holographic transmission and produces a wave function collapse that we can measure in our spooky double slit experiment?
Reply | Report Abuse | Link to thisI explained how to find a wave function drop without causing it to happen before.It took me years of thought experiments to figure it out.the experiment is set as thus.First you set up 2 two slit experiments,both are closed systems.In each box you attach two fiber optics the back of the box where the interference appears,you make the card that holds the optics adjustable so you can slide it back and forth in front of the pattern.The object is for one optic to be in the light and the other in the dark.then both optics on both boxes go to four different photodetectors,with the detectors going to the lighted part of the patterns in both box's turned off thus not detecting.the other detectors in the dark part of the pattern are turned on.When wave function is present the the dark pattern detectors show nothing going on.now you attach the experiment to source.The source is now split with each beam going to each of the two slit experiments.Now inside both boxers there is an interference pattern.Now if you you turn on either detectors in the lighted area.the wave function patterns drop,and light now reaches the detectors in the dark area of the pattern setting them off.Now you detect wave function drop with out causing it.Now when lighted detectors are off and wave function is present that = 1,and when where the dark area detectors are detecting light the wave function has dropped and that=0.Now you can send a binary signal with no direct connection between the boxes and the slit beam light is moving only one direction.Now you only need to make the source some starlight.And have the persons on the other end have things set up the same way.Then we look for a star that is the same distance away from both ends.Even though the light may be from light years away,the photons are entangled because the are from the same source.Now when a person on the other end turns on their lighted area detector,the detector on our end in the dark area detects the wave function drop.Thus communication in real time across light years is possible.The who thing above looks simple,but it took me decades to figure it out.I have been working on it since junior high school when a teacher told me it was impossible.Now you can see why you can not use the light from the actual source, the light being used must be the same age,and the same group of entangled photons for it to work.
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