Wavefunction Collapse: Measuring Electron Spin

[dEdt]

If you were to measure an electron's spin, for example, will the wavefunction associated with its position also collapse?

 

[xts]

Those two ('measurement' and 'collapse') are virtually synonyms.

 

[DrChinese]

If you were to measure an electron's spin, for example, will the wavefunction associated with its position also collapse?

That is not a requirement of a measurement (or collapse). In other words, measuring one does not collapse all.

 

[K^2]

You have to be more specific. If your measurement is equivalent to spin operator, it does not collapse the spatial components of the wave function. But any realistic measurement will probably collapse the spatial wave function to something. Really, it depends on how you measure the spin in the first place. Stern–Gerlach, for example, obviously collapses the spatial wave function as well as the spin wave function.

 

[DrChinese]

You have to be more specific. If your measurement is equivalent to spin operator, it does not collapse the spatial components of the wave function. But any realistic measurement will probably collapse the spatial wave function to something. Really, it depends on how you measure the spin in the first place. Stern–Gerlach, for example, obviously collapses the spatial wave function as well as the spin wave function.

I would not have thought an S-G outcome would contain much position information.

 

[dEdt]

I would not have thought an S-G outcome would contain much position information.

I think an S-G device also gives an indication of what path the object took inside the device itself. Wouldn't that collapse the wavefunction?

At any rate, have there been any experiments done to check that say spin collapse doesn't cause position collapse? Or is this based on theoretical arguments?

 

[DrChinese]

I think an S-G device also gives an indication of what path the object took inside the device itself. Wouldn't that collapse the wavefunction?

At any rate, have there been any experiments done to check that say spin collapse doesn't cause position collapse? Or is this based on theoretical arguments?

As K^2 says, it depends on the specific setups. Mostly this is based on theoretical considerations as it is quite difficult to actually test. However, there have been actual experiments done on entangled pairs which show that entanglement on one basis can survive collapse on another.

http://arxiv.org/abs/quant-ph/0406148

Abstract: "We report on the the experimental realization of hyper-entangled two photon states, entangled in polarization and momentum."

 

[xts]

At any rate, have there been any experiments done to check that say spin collapse doesn't cause position collapse?

You can make it yourself. Prepare Young's double slit experiment putting polariser at slits (the same polarisation in both of them). Spin gets collapsed, but you still see fringe pattern.

 

[K^2]

I would not have thought an S-G outcome would contain much position information.

You are effectively measuring position and use it to determine the spin. You can't really do that without collapsing the position wave function.