New answers tagged wavefunction-collapse
3
votes
Does the collapse axiom predict non-physical states in the case of measurement of continuous-spectrum quantities?
Suppose you have an electron interacting with a Geiger counter. There is a description of what is happening in terms of some quantum field theory such as QED. Those equations describe what is ...
- 9,308
4
votes
Accepted
Does the collapse axiom predict non-physical states in the case of measurement of continuous-spectrum quantities?
Since my name directly appears in the question, I think that I should try to answer. Also because I substantially changed some ideas about some of these issues in the last years.
First of all, the ...
- 75.8k
0
votes
Another Entanglement Question - Can you tell if the wave function of an entangled particle is collapsed?
First, a discussion of collapse. The motion of a quantum system in general depends on what happens to all of its possible states, e.g. - during a single particle interference experiment, all of the ...
- 9,308
2
votes
Accepted
Weak measurements, non-demolition measurements and interaction-free measurements vs. wave function collapse
The equations of motion of quantum theory such as the Schrodinger equation or any of the equations of quantum field theories such as QED don't imply and aren't consistent with wavefunction collapse. ...
- 9,308
3
votes
Another Entanglement Question - Can you tell if the wave function of an entangled particle is collapsed?
No, you can't tell what has happened far away if all you have access to is the local system, even if your local system is entangled with the far-away system. This is a consequence of the "no-...
- 1,959
2
votes
Another Entanglement Question - Can you tell if the wave function of an entangled particle is collapsed?
Any time you make a quantum observation, the wave function of your system collapses in the sense that it gets projected onto the eigenspace of your observable that corresponds to the observed outcome. ...
- 16.4k
2
votes
Accepted
How do I calculate the probability distribution of momentum assuming that my instrument has a small spatial extension?
One way to carry out this experiment and illustrate some quantum strangeness is diffraction through a pinhole. You take a laser and point it at a screen with a slit in it. Some light hits the screen. ...
- 42.8k
5
votes
Accepted
Does measuring a quantum object collapse the wave function even if the particle is not found in the position where it was measured?
The "collapse of the wave function" is a very unphysical concept: It was invented within the Copenhagen Interpretation by people who tried to make sense of Quantum Mechanics, and who ...
1
vote
Does measuring a quantum object collapse the wave function even if the particle is not found in the position where it was measured?
You write:
Properties of quantum objects are determined by a wave function.
Not exactly. The wavefunction represents the evolution of the system. Sometimes that evolution involves what is happening ...
- 9,308
3
votes
Does measuring a quantum object collapse the wave function even if the particle is not found in the position where it was measured?
We are talking about a statistical law here. The probability of finding the particle in region $[x+\Delta x]$:
$$
P(x < X < x+\Delta x)=|\psi(X)|^2\Delta x=w
$$
This means that, after performing ...
- 62k
-2
votes
What experiments have been done which demonstrate that immediately after measurement, the collapsed state evolves unitarily again?
Really QM for high school? You should start by saying QM was invented in the 1930s/1940s and that WWII took all the best scientists into the nuclear age ... leaving QM at kind of a dead end and ...
- 2,757
1
vote
What experiments have been done which demonstrate that immediately after measurement, the collapsed state evolves unitarily again?
Several people here suggest using the Stern-Gerlach experiment for your experiment, but this is not a practical experiment to carry out in a classroom. If you want to actually do a real experiment for ...
- 7,686
0
votes
What experiments have been done which demonstrate that immediately after measurement, the collapsed state evolves unitarily again?
@Codename47 is right, I think the best experiment to explain how orthodox quantum theory thinks about experiments on quantum systems (including collapse of quantum state on measurement and validity of ...
- 39.8k
0
votes
Are there any theoretical reasons why we cannot measure the position of a particle with zero error?
You might try a thought experiment: how can I measure the position of a particle with minimal (ideally zero) error? This is how my sixth form physics teacher introduced Heisenberg's uncertainty ...
- 307
1
vote
In the tunneling effect, to find a particle inside the barrier must I necessarily supply energy to the particle?
So to find the particle in the barrier must my measurement operation necessarily supply energy?
No, because we know examples of quantum tunneling which have nothing to do with measurement in the ...
- 39.8k
13
votes
Are there any theoretical reasons why we cannot measure the position of a particle with zero error?
Continuous variables can't be measured with zero error in principle, already due to them being real numbers, nothing to do with quantum theory. It would take infinite number of digits to write down ...
- 39.8k
-1
votes
Are there any theoretical reasons why we cannot measure the position of a particle with zero error?
The Planck length is hypothesised as the minimal length measurement, so we shouldn't expect to measure the position of an electron with uncertainty much smaller than this value.
- 13.2k
6
votes
Are there any theoretical reasons why we cannot measure the position of a particle with zero error?
In quantum mechanics the two variables
(i) position x and
(ii) momentum are "correlated" in the sense that if we multiply their uncertainties, they have to exceed a certain number. This is ...
- 9,024
6
votes
Accepted
In the tunneling effect, to find a particle inside the barrier must I necessarily supply energy to the particle?
Since the new wave function is in a region with potential energy $V_0$, the total energy $E_2$ (potential plus kinetic) associated with the state must be equal to or greater than the potential energy $...
- 62k
Top 50 recent answers are included