Quantum Entanglement of Photons: Exploring the Effects of Rotating Local Basis

In summary, A question was asked about entanglement and after researching on Wikipedia, it was found that photons can be entangled in a way that their polarization states are a superposition of vertical and horizontal polarization. However, when the example was altered to have the photons with opposite polarizations, the resulting calculation was contradictory to the entanglement. The accuracy of the Wikipedia entry was questioned and assistance was requested in properly calculating the entangled state.
  • #1
fulis
6
0
A question came up about entanglement and I've only studied very little QM so far, so I went to wikipedia to see if I could become any wiser and they had an example on photon entanglement which was quite straight forward (though the whole page lacks sources =[ ). The example shows that if you have photons going in opposite directions and that are entangled such that they will have the same polarization and their state is a superposition of vertical and horizontal polarization states then they actually don't have a polarization. Kind of a neat result.

Anyway, I figured I'd try to change the example a bit by having the two photons have opposite polarizations instead, so instead of the state:
|1,V>|2,V>+|1,H>|2,H>
I used:
|1,V>|2,H>+|1,H>|2,V>

I did the exact same substitution for the V and H states as they did in the example. I was expecting to get:
|1,45>|2,135>+|1,135>|2,45> since the photons are entangled in such a way that they have opposite polarization, but instead I got (I haven't normalized any of these expressions):
|1,45>|2,45>-|1,135>|2,135>

which is contradictory to the entanglement. The actual calculation is really simple and I did double check it a few times so I'm guessing the problem is something else. It's not exactly the best written wiki entry so I don't trust it to be right :D if someone else could show me how you actually calculate it I'd be grateful
 
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  • #2
You'll have to be more precise... |1V>|2H> + |1H>|2V> seems to me like a perfectly formed quantum state of two photons (modulo normalization, of course). Why do you rotate the local basis?
 

1. What is photon entanglement?

Photon entanglement is a phenomenon in quantum mechanics where two or more particles become correlated in such a way that the state of one particle is dependent on the state of the other(s), regardless of the distance between them. This means that measuring the state of one particle (such as its polarization or spin) instantaneously affects the state of the other particle(s), even if they are separated by large distances.

2. How does photon entanglement work?

Photon entanglement occurs when two or more particles are created or interact in a way that their quantum states become correlated. This means that their properties, such as spin and polarization, are linked in a way that measuring the state of one particle instantly affects the state of the other(s). This correlation persists even if the particles are separated by large distances, making it a unique and fascinating phenomenon in quantum mechanics.

3. What is the significance of photon entanglement?

The significance of photon entanglement lies in its potential applications in quantum communication and computing. Because entangled particles can be used to transmit information instantaneously over large distances, it has the potential to greatly improve communication and computing technologies. It also plays a crucial role in tests of fundamental principles in quantum mechanics and has led to advances in our understanding of the nature of reality at the quantum level.

4. How is photon entanglement measured?

Photon entanglement can be measured by performing a series of experiments on the entangled particles. These experiments typically involve measuring the state of one particle and observing how it affects the state of the other(s). If the particles are truly entangled, the results will show a strong correlation between the states of the particles, even if they are separated by large distances. Various technologies, such as photon detectors and quantum computers, can be used to measure photon entanglement.

5. Can photon entanglement be used for faster-than-light communication?

Although photon entanglement allows for instantaneous communication over large distances, it cannot be used to transmit information faster than the speed of light. This is because, while the state of one particle may be affected instantaneously by measuring the other, the actual transfer of information between the particles still obeys the laws of relativity. Therefore, while photon entanglement has potential applications in communication and computing, it cannot be used for faster-than-light communication.

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