Bizarre Quantum State Entangles a Record 3,000 Atoms
The large number of entangled particles could improve the accuracy of GPS and atomic clocks.
Using a single particle of light, scientists have for the first time linked together thousands of atoms in a bizarre state known as quantum entanglement, where the behavior of the atoms would stay connected even if they were at opposite ends of the universe.
This finding, the largest number of particles that have ever been mutually entangled in an experiment, could lead to more precise atomic clocks, potentially helping to improve GPS, researchers say.
The behavior of all the known particles can be explained using quantum physics. A key feature of quantum physics is that the world becomes a fuzzy, surreal place at its very smallest levels.
For instance, atoms and other fundamental building blocks of the universe actually exist in states of flux known as "superpositions," meaning they can seemingly be located in two or more places at once.
One consequence of quantum physics is quantum entanglement, wherein multiple particles can essentially influence each other simultaneously regardless of distance.
Einstein dismissed this seemingly impossible connection as "spooky action at a distance," but numerous experiments have proven quantum entanglement is real, and it may serve as the foundation of advanced future technologies, such as incredibly powerful quantum computers and nigh-unhackable quantum encryption.
One key application of quantum entanglement is to enable extraordinarily precise atomic clocks, which are vital to GPS. "Today's atomic clocks have reached an almost unimaginable level of accuracy -- the best would be less than a minute off if they ran since the Big Bang," study co-author Vladan Vuletic, a quantum physicist at MIT, told Live Science.
Today's best atomic clocks are based on oscillations seen within a cloud of trapped atoms, which make them essentially act like pendulums, keeping a steady beat. A laser beam fired through such a cloud can detect the vibrations of the atoms and use them to tell time. The accuracy of atomic clocks improves as more and more atoms oscillate within a cloud.
Since entangling atoms links their behavior, the more atoms researchers entangle, the more they might oscillate together, improving their use in timekeeping.
Until now, scientists had entangled together 100 atoms at most. Moreover, these atoms represented only a small fraction of the larger clump of atoms in the experiment.
Now Vuletic and his colleagues have successfully entangled together nearly 3,000 atoms, almost all of the cluster of 3,100 atoms they were a part of. Moreover, they did so using only single photons, which are particles of light.
"The fact that you can influence so many particles with just one single photon is the most surprising finding," Vuletic said.
The researchers first cooled a cloud of rubidium atoms to only a few ten-millionths of a degree above absolute zero, the coldest possible temperature. They next trapped the atoms between two slightly transparent mirrors and fired weak laser pulses through one of the mirrors.
The pulses contained as little as a single photon, and bounced back and forth between the mirrors, passing about 5,000 times through the cloud. [How Quantum Entanglement Works (Infographic)]
A photon can be thought of as a wave oscillating in space. If a photon in one of the laser pulses passed through the cloud without interacting with any of its atoms, the polarization of the photon - the orientation of its ripples - would remain the same.
If a photon in a pulse interacted with the cloud's atoms, the polarization of the photon would rotate slightly. Strangely, in the realm of quantum physics, the act of measurement can dramatically influence the object getting measured, and the act of detecting a photon that interacted with these atoms can essentially generate entanglement between those atoms.
The key to the research team's success was using extremely weak pulses of light. "Previously, experiments used far more photons, tens of thousands or millions of photons, which added a lot of noise to the experiments," Vuletic said. "We just used single photons, which perturbed the atomic ensembles much less."
The researchers suggest it should be simple to entangle together still more atoms. "We could go to entangling a million atoms relatively straightforwardly," Vuletic said.
The scientists are currently using this single-photon detection technique to build a state-of-the-art atomic clock, "which could improve timekeeping by a factor of two," Vuletic said. In addition, the researchers aim to achieve even more complex entangled states - the kinds needed in applications such as quantum computing.
Vuletic and his colleaguesdetailed their findings in the March 26 issue of the journal Nature.
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An illustration shows a large number of atoms (purple) mutually entangled with one another.
Top 5 Sci-Fi Time Travel Methods
There is no shortage of time machines in the world of science fiction. You could probably name a bunch of them off the top of your head, from H.G. Wells' iconic creation to such mainstays as Dr. Who's Tardis and Dr. Brown's flux-capacitated DeLorean. But just how many fictional time machines can you explain? In many works of fantasy and science fiction, the time machine is just a magical plot device. No actual science is thrown at the audience. Most of the time, no one asks for any. After all, you're probably not watching Life on Mars or Terminator Salvation for a lesson in theoretical physics. Plus, if you're writing time-traveling fiction, then skipping the science spares you the embarrassment of getting something wrong. Isn't it enough that you described 1997 as being a world full of flying cars and busty android life partners? Let's take a look at five examples of the plausible and ridiculous ways fictional TV and film characters have traveled through time.
5. Superman Spin Control
If we learned anything about the physics of time and space from Richard Donner's 1978 film Superman, it's that if you fly around the Earth really fast, you can reverse its rotation and roll back time. Although physicists agree that space and time are interconnected, you'd be hard-pressed to find anyone who would back the "science" behind reversing planetary rotation to turn back time. Far from saving Lois Lane's life, the feat likely would have caused global chaos. Slam on the brakes in a moving car and everything inside it continues moving forward. Now imagine this scenario on a global scale, only with oceans, mountains and weather systems continuing to surge forward at up to 1,000 miles per hour, depending on your latitude. Way to go, Superman.
4. The Voyage Home to 1986
The Star Trek universe is full of fantastic ideas: aliens with rippled foreheads, holodecks and more time travel than you can shake a stick at. According to the Star Trek Wiki, 50 episodes of the six TV series featured time travel, as did four of the 11 films. You'd think the space-time continuum would just be circling the drain after all that tinkering. Time paradoxes aside, Star Trek always flirted with real science. Take 1986's Star Trek IV: The Voyage Home, for example. In this film, the crew of the Starship Enterprise send a Klingon Bird-of-Prey vehicle back to the 1980s by sling shotting it around the sun. The Star Trek slingshot method involves using the sun's gravitational pull as an accelerator to reach speeds necessary to travel through time. The premise falls in line with some theories about time travel and Einstein's theory of special relativity. The theory says if time slows the closer you get to the speed of light, then travel into the future -- or the past -- may be possible. One slight problem: faster-than-light travel is physically impossible. Plus, as Lawrence M. Krauss points out in The Physics of Star Trek, the gravitational field near the surface of the sun doesn't produce anywhere near the boost you'd need to go talk to whales in the past.
3. Trekking into a Black Hole
Paradoxical time travel isn't a thing of the past for the Star Trek legacy. The plot of the new film concerns two starships that are sucked into an artificial black hole, sending them 154 years into the past. While the time-travel method employed in Star Trek IV: The Voyage Home depended on a far too weak gravitational slingshot, many physicists believe that a black hole might indeed provide the necessary portal to the past. Anything that crosses a black hole's event horizon heads toward an incredibly tiny point of infinitely compressed matter called a singularity. That's also one of the huge problems with the new Star Trek film's plot: What's to keep the two starships from winding up as one with the singularity? Physicists point to Kerr black holes as a less destructive alternative. These theoretical cosmic phenomena first described by Roy Kerr in the 1960s lack the matter-smashing singularity at the center, potentially making it possible to pass the event horizon and come out the other side -- in another time.
2. Donnie Darko, Creepy Rabbits and Wormholes
The 2001 cult favorite Donnie Darko spends most of its time exploring the possible effects of time-travel paradoxes and tangent universes on its characters, but it also features a portal through time: a wormhole. Also called Einstein-Rosen bridges, these hypothetical cosmic structures might offer a traveler the necessary means of not just taking a shortcut through space, but also through time itself. Einstein's theory of relativity states that mass curves in spacetime. The most common visual example of this concept is that of space depicted as a curved, two-dimensional plane. Think of a racetrack: If you're speeding around a curve, you're bound to that curve, but what if you could forge a new line of track between its two parallel sides? That's the idea behind a wormhole. If a mass on one side of the spacetime curve applies enough force and a mass on the other side of the spacetime curve applies enough force, then the two could meet, creating a tunnel.
1. Lost on a Time-Traveling Island
If you've watched ABC's "Lost," then you're probably used to things not making a lot of sense. A big reason for this is that the show's mysterious island bounces the characters around through time seamlessly. Seriously, by the end of the series, everyone will be lucky to make it off the island without becoming their own grandparent. Yet "Lost" at least makes an effort to prop up the fiction with a little science. According to blog analysis at Popular Mechanics, the science behind the show's time travel seems to depend on quantum mechanics, a mysterious substance in the ground called "exotic material" and possibly a wormhole. Might this buried, volatile substance produce the necessary energy to manipulate a breach in spacetime? To varying degrees, you could argue that this is all any writer can achieve when crafting a piece of time-travel fiction -- not counting writers who are actually from the future, of course.