What is Entangled particles: Definition and 62 Discussions
Quantum entanglement is a physical phenomenon that occurs when a group of particles are generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the group cannot be described independently of the state of the others, including when the particles are separated by a large distance. The topic of quantum entanglement is at the heart of the disparity between classical and quantum physics: entanglement is a primary feature of quantum mechanics lacking in classical mechanics.
Measurements of physical properties such as position, momentum, spin, and polarization performed on entangled particles can, in some cases, be found to be perfectly correlated. For example, if a pair of entangled particles is generated such that their total spin is known to be zero, and one particle is found to have clockwise spin on a first axis, then the spin of the other particle, measured on the same axis, is found to be counterclockwise. However, this behavior gives rise to seemingly paradoxical effects: any measurement of a particle's properties results in an irreversible wave function collapse of that particle and changes the original quantum state. With entangled particles, such measurements affect the entangled system as a whole.
Such phenomena were the subject of a 1935 paper by Albert Einstein, Boris Podolsky, and Nathan Rosen, and several papers by Erwin Schrödinger shortly thereafter, describing what came to be known as the EPR paradox. Einstein and others considered such behavior impossible, as it violated the local realism view of causality (Einstein referring to it as "spooky action at a distance") and argued that the accepted formulation of quantum mechanics must therefore be incomplete.
Later, however, the counterintuitive predictions of quantum mechanics were verified in tests where polarization or spin of entangled particles was measured at separate locations, statistically violating Bell's inequality. In earlier tests, it couldn't be ruled out that the result at one point could have been subtly transmitted to the remote point, affecting the outcome at the second location. However, so-called "loophole-free" Bell tests have been performed where the locations were sufficiently separated that communications at the speed of light would have taken longer—in one case, 10,000 times longer—than the interval between the measurements.According to some interpretations of quantum mechanics, the effect of one measurement occurs instantly. Other interpretations which don't recognize wavefunction collapse dispute that there is any "effect" at all. However, all interpretations agree that entanglement produces correlation between the measurements and that the mutual information between the entangled particles can be exploited, but that any transmission of information at faster-than-light speeds is impossible.Quantum entanglement has been demonstrated experimentally with photons, neutrinos, electrons, molecules as large as buckyballs, and even small diamonds. The utilization of entanglement in communication, computation and quantum radar is a very active area of research and development.
Let us say we have a EPR type experiment using entangled electrons. If the two observers have their detectors orientated so that they make correlating detections, then as I understand it, if one observer makes positive detections of electrons with "up spin" then the other observer has to make...
Hi,
This is my first post here. I have done some reading on quantum mechanics and am curious to know more.
I know about the double slit experiment and the interference pattern produced. I have also read of entangled pairs.
My main question is:
If you have a pair of entangled...
Whenever you read about entangled particles, and how measuring one of them "immediately" changes the other, the problem of faster than light travel is usually dismissed with "o, but you can't use it to transmit information, so it doesn't contradict relativity".
However, I think there's a more...
I have been reading quite a bit about bell pairs lately and would like to know about the actual experimental behavior of them. Here is a summary of my current understanding:
Take two particles A and B entangled in such a way as the spin of each is opposite to the other, or in other words, a...
We know that if, for example, two particles are entangled in a state like: |Ψ>=a |0>|0> + b |1>|1>, then measuring an observable on only one of the particles it makes the interference dissapear.
But isn't it impossible to measure both particles simultaneously in order to maintain the...
I am a Combat Medic in the US Army and have a few questions to ask. I am not a physicist nor would I pretend to be. I am just a curious mind. I am very new to this so these questions may be very simple.
1. Is it possible to capture an entangled particle?
2. If so can these particles be...
Ok, here's my problem... In the EPR experiment it is described that if entangled particles are required to be able to cancel each others spin's then no mater how far apart these particles are, if one is measured you can instantly infer the state of the other particle. Why would the other...
I asked this question over in the QM forum, but it fizzled out there. I think it's more appropriate here anyway so I'll post it. If this is against forum rules, I apologize!
I'm reading a paper on decoherence (preprint http://arxiv.org/abs/quant-ph/0105127" ), and am afraid I don't grasp one...
I am puzzled with the following gedankenexperiment.
Consider a pair of particles that are sent from x = 0 on different directions +x and -x with entangled position on the y axis.
Parallel to the y-axis we locate two double slit plates A and B. They plate A is located at x = -L and the plate B...
I've been doing more reading so forgive me. I read all the time where testing is being done with entangled particles to test their spin but no real explanation of how you entangle them.
The best I can surmise is that they are two particles that have been run into each other and bounce off...
Two photons are emitted from the same point in a crystal and they travel in opposite directions.I find the direction one photon is moving in and this
means I instantly know the direction of the other photon.But the other
photon had passed an event horizon into a black hole when I made my...
"Entangled Particles" Allow for absolutely crazy things?
I was reading a little bit about entangled particles... I can't be sure how much of it I grasped, but as I understand it for every particle in the universe spinning in direction X, there is another particle spinning in the exact opposite...