Category: bell inequality test

Physicists Take One Large Step Towards Proving Quantum Entanglement

New Loophole-Free Bell Test

One of the most interesting (and confusing) phenomena in quantum physics is quantum entanglement. We observe this quantum effect when we see entangled particles affect each other regardless of distance. For example, when we measure the state of one particle at a distance from another and the measurement of the state of the first instantly influences the state of the other, we have quantum entanglement.

Einstein was disturbed by this, and didn’t like the idea that quantum entanglement might violate the speed of light if the particles were somehow sending each other information faster than light could travel. Therefore, he developed the idea of local realism, which assumes a pre-existing value for any possible measurement of a particle — an objective value a particle must have. This theory is based on the idea of locality, the principle that there is a minimum amount of time it takes for distant objects to influence each other, and realism, the idea that objects exist whether or not they are measured.

In the 1960s, Physicist John Bell developed a famous test to determine whether particles really do influence each other in the way quantum entanglement suggests. In the Bell test, a pair of entangled particles are sent in different directions toward different locations. A device measures the state of each particle in each location, and the settings of each device are set at random; this way it’s impossible for device one to know the setting of device two at the time of measurement, and vice versa.

If quantum entanglement is real, then local realism shouldn’t work, and the Bell inequality test should be violated. If scientists do observe violations of the Bell inequality test, it means that quantum mechanics violates locality, realism, or both — making local realism incorrect. In recent research, physicists have reported some of the best evidence to date that quantum entanglement exists, and the quantum world is free of the constraints of local realism. Researchers performed a Bell inequality test that was, essentially, loophole-free, and demonstrated that two atoms one-quarter of a mile apart shared correlations probably caused by quantum entanglement. According to local realism, this should be impossible.

Image Credit: Rosenfeld et al. Published by the American Physical Society
Image Credit: Rosenfeld et al. Published by the American Physical Society
The only way the observed correlations could be explained by local realism would be if there were unknown “hidden variables” instead of quantum entanglement. And, according to the researchers, the odds of this being the case are less than one in a billion. The odds drop even further once all seven months of their accumulated data is accounted for, dipping to about one in ten quadrillions. The team concluded that the laws of the quantum world violate locality, realism, or possibly both.

Closing Loopholes

Although the test in this research was essentially loophole-free, all loopholes are not completely closed. One of the last possible loopholes that remain for most Bell tests has to do with how particle states are measured. It is critical that hidden variables are not somehow allowing particles to synchronize their properties by influencing the choice of measurement. This is called the freedom of choice or free-will loophole. In this research, the team used a high-speed quantum random number generator to eliminate this loophole, but the minuscule possibility of communication between random number generators or with other experimental elements technically remains possible.

Other research has used humans to randomly choose numbers, relying upon the randomness of unique human minds. The physicists in this study felt that an extraterrestrial random number generator is the only way to truly close the loophole since such massive distances would prevent covert communication. There are several such extraterrestrial random number generators under development in physics labs now, intended for this purpose.

Closing the loopholes matters, because scientists hope to use quantum entanglement to safely encode messages. The demands of quantum cryptography would mandate further refinement of the measurement process. Ultimately, the hope is that quantum entanglement will allow us to transmit quantum information over long distances almost instantaneously, making quantum computing and interstellar communication possible.

The post Physicists Take One Large Step Towards Proving Quantum Entanglement appeared first on Futurism.

Get Involved in the World’s Biggest Quantum Physics Experiment Happening Right Now

What could be the world’s largest quantum physics experiment is happening today, 30 November 2016, and researchers need people from all over the world to get involved by helping them test the laws of quantum mechanics.

The experiment, run by 12 different labs around the world, will test Albert Einstein’s idea of local realism – one of the fundamental principles of quantum mechanics. All you have to do to help out is play a bunch of online games for science.

So, what will all your gaming efforts achieve? Basically, local realism is an attempt to overcome what Einstein referred to as “spooky action at a distance.”

In quantum mechanics, there are two things to keep in mind. First, particles don’t have a distinct value until they’re measured. And secondly, when two particles are entangled, one of them will immediately affect its entangled partner, no matter how physically far apart they are.

Einstein didn’t like that, because, in theory, it seems to violate the speed of light – hence the “spooky action” quote.

So he came up with the idea of local realism, which assumes that a particle must objectively have a pre-existing value for any possible measurement – and that way, information doesn’t actually travel between two entangled particles faster than the speed of light.

Since then, researchers have come up with a test to measure whether or not information is actually travelling between entangled particles, known as the Bell inequality test.

And if it’s violated in actual experiments, it implies that quantum mechanics violates either locality or realism, and the idea of local realism (and Einstein’s hypothesis) therefore cannot be correct.

Several experiments over the past few years have reportedly violated Bell’s inequality – last year, the first Bell’s inequality experiment was completed without loopholes, but there’s still dispute over whether or not local realism actually holds up.

The new worldwide experiment aims to settle the matter once and for all, by using a huge amount of random, user-generated data to test Bell’s inequality.

Basically, the researchers are holding what’s called the ‘BIG Bell Test: worldwide quantum experiments powered by human randomness‘, and they aim to conduct a range of Bell’s inequality tests around the world, controlled by human decisions made by volunteers (which they call Bellsters).

The experiment needs at least 30,000 volunteers from all over the world, and of all ages, to take part in order to generate enough random data to properly test out Bell’s inequality.

You do this by playing a game where you have to introduce the most random sequences of 0s and 1s as possible. These sequences you generate in your game will determine the order of measurement of quantum entangled particles in each lab around the world.

The loophole-free Bell’s test last year was similar, but it used a physical random number generator to come up with this data, whereas the new experiment will try to generate even more randomness using the brains trust of the internet.

The games are accessible to people of all ages, and all you need is an internet connection.

If you pass all the levels, you’ll have generated enough random sequences of information to help the scientists complete their Bell’s inequality test.

Click here to get involved. For science!

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