# Diminishing wave-functions

1. Sep 22, 2015

### Einstein's Cat

Is it possible to reduce the amount of possible locations of a particle along a wave function without causing the wave function to collapse? Thank you for your help and of I'm simply being ignorant then please say!

2. Sep 22, 2015

### ZapperZ

Staff Emeritus
You will need to elaborate quite a bit more on your question, because as it is, it sounds like a word salad. What exactly is ".. reduce the amount of possible locations of a particle ALONG A WAVE FUNCTION...."?

Zz.

3. Sep 23, 2015

### Einstein's Cat

So wave- duality means a particle can act both as a particle and as a wave. A wave function is used to describe the wave, the particle is behaving as. Thereby somewhere along the wave function is the particles position. However because the particles position is in a superposition along the wave function there are many possible places the particle is. My question was that if someonw could reduce the number of possible places the particle is located along the wave function to say a fifty-fifty where the particle is somewhere, if not the other. However doing all these without collapsing the wave function. Thank you for your help

4. Sep 23, 2015

### Demystifier

Yes, it's possible, e.g. by turning on a confining potential.

5. Sep 23, 2015

### ZapperZ

Staff Emeritus
Have you done basic QM problems such as the one done for an infinite square well? Isn't this an example where the particle is confined to a specific volume of space but still "uncollapsed"?

Zz.

6. Sep 25, 2015

### jfizzix

Anything you do to a particle will disturb its wavefunction in one way or another.
If you perform only a slight partial measurement (only learning a little about say, its position), you disturb the wavefunction a correspondingly little amount.

So, you can reduce the number of possible locations of a particle, but the more you narrow down its position, the stronger that measurement disturbs the wavefunction, and the less you'll be able to learn about other observables (like momentum).

Wavefunction "collapse" isn't necessarily an all-or-nothing phenomenon, but can occur in degrees. Measurement can be described as a physical interaction between object and measurement device, also covered by the laws of quantum physics.

As one neat example, it's possible to measure both the position and momentum statistics of a beam of light, by doing multiple partial measurements in position, while measuring strongly in momentum.
See for example: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.253602

7. Sep 27, 2015

### Einstein's Cat

Thank you very much for your help