- #1
Chris Miller
- 371
- 35
source = http://scienceblogs.com/principles/2012/03/14/entanglement-is-not-that-magic/
It's not clear to me from the above whether this experiment is repeated on the same entangled pair of photons, or a different pair each time. Also, thanks to SR, I have trouble with the "when."
Would the following correctly paraphrase the above?
Particles are considered entangled if we know how to correlate their measurements, and not if we don't. In other words, there is still/always a correlation, we just don't know what it is.
To explain what I’m talking about, we need to consider an example, and how you describe matters mathematically. My background is in the quantum optics sort of world, so let’s think about an entangled state of two polarized photons, produced in a way that guarantees the polarization of the two will be exactly the same. If we think about linear polarization, there are two possible states, which are determined by the axis of a polarizer used to measure the state of one of the photons– by convention, we’ll call them horizontal (represented by |H>) and vertical (represented by |V>>). An entangled state then looks like:
|Ψ> = A(|H>1|H>2+|V>1|V>2
This wavefunction is the sum of two terms, one corresponding to both particles having horizontal polarization, the other corresponding to both particles having vertical polarization. If you measure the state of one of them, then, you can predict with certainty the state of the other, no matter how far away it is at the time you make the measurement. If you and a friend each take one photon and measure its state, horizontal or vertical, then repeat the experiment many times, when you compare your lists of measurements, you will find that they are always the same: when you find vertical polarization, your friend also finds vertical polarization, and vice versa.
It's not clear to me from the above whether this experiment is repeated on the same entangled pair of photons, or a different pair each time. Also, thanks to SR, I have trouble with the "when."
It’s just a correlation between measurement results, not a knob that let's you manipulate the states of distant particles.
Would the following correctly paraphrase the above?
Particles are considered entangled if we know how to correlate their measurements, and not if we don't. In other words, there is still/always a correlation, we just don't know what it is.