# Quick question on Quantum Entanglement

1. Jun 1, 2010

### Mr.Illusion

I'm sorry for the trouble, but I was hoping you guys could help me understand something about Quantum Entanglement.

So if I measure the x-axis spin of an electron and get +1, then that implies the the other particle must have spin -1, correct? Also, what if I measure the spin of the particle, 6 times in a row? Will I continue to get the same spin of the particle or will the spin still be random? I'm guess that as soon as I measure the spin the first time, the wave function collapses and I am left with a definite spin.

2. Jun 1, 2010

### DrChinese

Yup, that's it. You ask the same question, you get the same answer. (OK, maybe I oversimplified that one.)

3. Jun 2, 2010

### Geigerclick

You are right in the first, but in measuring once you break the entangled state, and need a new set of test particles. Now you are stuck with the probabilistic nature of QM as you measure unique pair, after unique pair.

4. Jun 2, 2010

### Mr.Illusion

Ah, so I guess that's why you can't send information instantaneously using Quantum Entanglement. Thanks for the help btw. I'm going to be visiting this forum more in hopes to better understanding Physics/Quantum Physics.

5. Jun 2, 2010

### Geigerclick

From what I've read, Dr. Chinese is the well deserved guru of entanglement, and welcome to PF!

6. Jun 3, 2010

### Mr.Illusion

Thank you, Geigerclick. I am actually going for my Ph.D in Mathematics (Almost finished with undergrad now). Mathematics is easily the most appealing of the Sciences to me; of course, Quantum Mechanics and Astrophysics are next. I really want to be a Theoretical Physicist one day, and I think there is no better way to start on that journey than here.

7. Jun 3, 2010

### unusualname

If you subsequently measure the spin along the same axis it will be the same each time. You only return to probabilistic results if you try to measure spin along a different orthogonal axis (spin in x,y,z directions cannot be simultaneously fixed)

You can demonstrate this by passing electrons through multiple filters arranged at different orientations in a Stern-Gerlach experiment. (Eg 50% will pass through the first "spin up" filter, but subsequently 100% of those will pass through another "spin up" filter)

eg http://www.upscale.utoronto.ca/PVB/Harrison/SternGerlach/SternGerlach.html

(The x-spin entanglement will be broken on the first measurement, it may be possible to measure in such a way that spin entanglement along the other orthogonal axes remains intact, DrC may have a reference)