Stack Exchange Network

Stack Exchange network consists of 175 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [wavefunction-collapse]

Wavefunction collapse amounts to the apparent reduction of a wavefunction consisting of a superposition of several eigenstates to a single eigenstate (by "observation"). It underlies measurement in quantum mechanics and connects the wave function with classical observables, in a thermodynamically irreversible interaction with a classical environment, normally disfavoring future QM interference.

2
votes
4answers
265 views

Does the wave function collapse cause information to be created?

If I understand correctly, a principle of physics is that information is never created or destroyed. And, unless information is defined differently in physics, according to information theory there is ...
1
vote
1answer
121 views

What is the relation between a measurement and an observable?

Observables are represented by Hermitian operators. First of all, it's a little strange (to me) that some measurable physical quantity is represented by a transformation (or linear map), given that I ...
1
vote
1answer
247 views

All of the postulates of quantum mechanics without additional information [closed]

$\newcommand{\braket}[2]{\left<#1|#2\right>}% \newcommand{\bra}[1]{\left<#1\right|}% \newcommand{\ket}[1]{\left|#1\right>}% $As an undergraduate who's trying to learn quantum mechanics it'...
0
votes
1answer
95 views

What is the physical basis of Born's interpretations?

Did anyone has any idea how Born came up with the probabilistic interpretation of quantum mechanics. It is by all means very bizarre. And then it leads to the idea of copenhagen interpretation. Also ...
1
vote
1answer
128 views

How does one make the wavefunction collapse into an eigenstate of a particular operator?

Say one has an unperturbed system that can be described with a wavefunction that is a superposition of many eigenstates. How does one make the wavefunction collapse into an eigenstate of say, the ...
2
votes
1answer
133 views

Does a photon's spin wavefunction collapse when detected by a photon detector?

Assume two entangled photons A and B have the same spin but travel in different directions. When Photon A is detected by photon detector (e.g. photomultiplier) on its path, does Photon B's spin wave ...
1
vote
1answer
78 views

Wave function collapse, EPR paradox and information transfer

For a classical formulation of the EPR paradox, two particles are produced, with total momentum zero and separated by a long distance. So say we measure the momentum of one particle first, and measure ...
2
votes
3answers
83 views

Is there an objective asymmetry between a collapsed and un-collapsed wave function?

In a quantum double slit experiment, one starts at t0 with a wave function that propagates through two slits, interferes, and probabilities for various positions at the final stage at t1 can be ...
20
votes
3answers
869 views

What are the strongest objections to be made against decoherence as an explanation of “collapse?”

When we measure an observable A of a quantum system, we get an eigenvalue of A. Without worrying about connotations of Copenhagen vs. MWI, etc., let's just call this "collapse." Question: Among ...
2
votes
1answer
92 views

Measurement of wavefunction collapse

I read in Griffith's quantum mechanics that In a particular system, the second time measurement of the position (say) would yield the same result (the same collapse or the same spike) given that ...
1
vote
1answer
94 views

Resource recommendation for interpretation of quantum mechanics?

The jumping of the quantum state to one of the eigenstates of $Q$ is the process referred to as state-vector reduction or collapse of the wave function (where $Q$ is an observable). I used to think ...
9
votes
3answers
907 views

When light reflects off a mirror, does the wave function collapse?

This question is specific to the Copenhagen interpretation, which states that the wave function collapses on interaction. If we have a beam of light reflected off a mirror, whether you see this light ...
1
vote
1answer
70 views

How is the wavefunction of an electron affected by the presence of an atom at the slits in the double-slit experiment?

I'm reading on page 107 of this Van Kampen's paper that the apparatus influences the electron even without detecting it. The interference pattern we obtained ...
7
votes
1answer
154 views

Is Quantum Mechanics time-symmetric?

In physics we have the CPT-theorem which guarantees time-reversal symmetry of dynamical evolution (although in some edge cases we will also have to reverse parity and charge). It seems clear enough ...
2
votes
2answers
60 views

When a wavefunction collapses on its own what basis does it project onto? (In Quantum Thermo, why do we privilege energy eigenstates?)

Obviously when an experimenter measures it, it projects onto the basis that the experimenter was trying to measure. But this process occurs on it's own, all the time. Obviously the answer has to do ...
7
votes
1answer
215 views

Can a measurement partially “collapse” a wavefunction?

Let's say I have a wavefunction $\Psi$ which can be decomposed into a sum of it's energy eigenstates: $$ \Psi = a|1\rangle + b|3\rangle + c|8\rangle + d|10\rangle$$ Where, of course, $|a|^2 + |b|^2 +...
0
votes
4answers
392 views

What is the deal with the Schrodinger's cat? Why is it considered a paradox?

What is the deal with the Schrodinger's cat? Why is it considered a paradox? Cat is a macro object. He can be only in 2 states - he's either dead or alive, the fact that you don't have the ...
2
votes
2answers
495 views

Can quantum particles spread out over large distances?

While trying to understand quantum mechanics I was wondering about this: since free quantum particles naturally spread out until the wave function collapses (if I understand correctly); does there ...
0
votes
1answer
60 views

Do we experience wave function collapse even though we don't read the detector?

In quantum double slit experiment would the the wave function collapse if we place a particle detector at the slit but do not read it and just keep looking at the screen?
-1
votes
3answers
163 views

A mismatch in quantum mechanics

One of the basic rules of Quantum mechanics is that after a measurement of an observable, the wavefunction is an eigenstate and any subsequent measurement will give the same result. This is not so in ...
-1
votes
2answers
261 views

Steps of measurement to verify the Heisenberg uncertainty principle

The answers here about experimentally verifying Heisenberg's uncertainty principle says the following. Step 3, select two operators A and B Step 4a, for some of the systems prepared in state $...
0
votes
1answer
97 views

Does the photon field extent exceed the distance ct?

Is the extent of the electromagnetic field of a photon limited to the event horizon of ct, where c=speed of light and t=time since photon generation? Or does some component of the field fill all space ...
0
votes
1answer
103 views

Understanding the Formalism of wave function collapse [duplicate]

For example, a perfect measurement ($\hat A=\hat x$) on position: $$\hat x\psi=x_0\psi$$ The eigenvalue $x_0$ is the result of measurement. The eigenfunction $\psi$ is the wavefunction after ...
0
votes
1answer
222 views

How did people think about the Copenhagen Interpretation before decoherence was discovered?

It seems today a lot of people are happy to think about quantum mechanics in terms of collapse theories, without thinking about where in the process the collapse occurs or what triggers it etc. This ...
2
votes
3answers
153 views

Does an asteroid superpose in space?

I'm learning the basics of quantum physics and I've read that all objects have a wave function, but the only reason nothing in the macro-world superposes is that they're constantly interacting with ...
1
vote
0answers
83 views

Can we measure without collapsing (too much) the wave function, according to decoherence theory?

According to decoherence theory, the collapse of the wave function is a continuous process due to interaction with environment. In a measure, there are interactions with photons (for example). Can we ...
0
votes
3answers
430 views

If uncertainty principle is explained by wave function, then doesn't wave function collapse when we measure position or momentum?

I have been using an app called Quantum on the play store. It says that the uncertainty principle can be explained by wave function, that is when we try to determine position , the wave function ...
0
votes
1answer
96 views

Could the collapse of a wave function be used to determine whether an object has been detected?

Consider a ship in space that is attempting to stealthily travel between two locations. I hypothesize that it could use the collapse of a wavefunction to tell if it's been detected by using a ...
-1
votes
2answers
58 views

Is the wave function collapse and the collapse of a superposition related?

It seems that they are two different types of collapses within quantum mechanics. But are they somehow related, or is it two completely different collapses? Sorry if the answer is obvious, and I have ...
1
vote
0answers
62 views

If measurement cause collapse of wave function, does it mean that any other interactions also collapse wave function? [duplicate]

I searched through many discussion on Physics Stack Exchange about "Why observation cause collapse of wave function?" and I am totally confused. Is it already solved by modern quantum physics? I know ...
1
vote
1answer
110 views

Energy-time Heisenberg inequality and wave-function collapse

Consider a two state system (2-state atom for instance) where each state corresponds to a different energy: $\left|\psi\right> = \frac{1}{\sqrt{2}}\left|0\right> + \frac{1}{\sqrt{2}}\left|1\...
15
votes
6answers
2k views

If a wave function collapses into one state, does it ever go back to a superposition of states?

It is my understanding that after an observation, the wavefunction collapses to one state. Thus, if you do an observation right after an observation (that collapsed the wavefunction), you get the same ...
0
votes
1answer
123 views

Does an electromagnetic field collapse the wave function of an electron?

In the double slit experiment, If there was an electromagnetic field at the slits, would the electron still create an interference pattern? Or would the presence of the field collapse the wave ...
6
votes
3answers
2k views

What processes cause the collapse of a wavefunction and break entanglement?

This question states that measuring the spin of an entangled particle causes the collapse of the wavefunction and thus the entanglement is broken. Then this question states that we don't know what ...
0
votes
2answers
97 views

Decoherence/wave function collapse between entangled photon pair

If photon 1 and 2 are position entangled and they go in different directions, would making a measurement on photon 1 effect photon 2? If photon 1 is detected can photon 2 still create interference?
0
votes
1answer
250 views

Wave function collapse of entangled photons?

If we have two entangled photons then they are described by the same wave function. But if I measured the position of the signal photon and it collapses into a position, would the idler photons ...
1
vote
3answers
123 views

When exactly is “God playing dice”? (Question on Hamiltonian and ground state, actually)

There is something I don't get: So I read that by applying an operator to the wavefunction (aka. measuring stuff), it is as if the wavefunction collapses onto one defined state which is an eigenstate....
0
votes
0answers
86 views

can any eigenfunction be normalizable ? If not why? and If yes How?

As it is told in quantum mechanics that a wave function has to be normalizable otherwise it won't express any physical situation. And this is too known that measurement or observations collapses ...
1
vote
4answers
620 views

After measuring momentum, it seems like the particle's position could be literally anywhere?

Once measuring momentum, the wavefunction "collapses" into something that looks like this If you were to then measure the position, couldn't it be literally anywhere? What am I missing? Is it even ...
2
votes
4answers
437 views

Wavefunction Collapse and Energy Conservation (and Stationary Tunneling)

Let's say I have a simple isolated quantum system of one particle, 1-D, without spin or relativistic effects. The system was prepared in a way that it begins in an eigentstate of the Hamiltonian, with ...
1
vote
0answers
433 views

Decoherence time of quantum decoherence and appearance of wavefunction collapse

If decoherence time of quantum decoherence is zero, or if off-diagonal elements of density matrix of quantum system (without environment considered) vanished immediately after interaction with ...
0
votes
1answer
613 views

Calculating the probability of eigenvalues from a superposition of two wave-functions

To calculate the probability of eigenvalues from a superposition of two wave-functions do you normalize the overall wave-funtion or the individual wave-functions. I am aware that one can write $\Psi =...
4
votes
1answer
223 views

Mathematical formulation of partial wave function collapse

If given a wave function which is an element of a Hilbert space $\mathcal{H}$ which is a tensor product of two other Hilbert spaces $\mathcal{H}_1\otimes\mathcal{H}_2$, how do you formulate ...
16
votes
2answers
717 views

Paradox of the wavefunction collapse into un unphysical state

"A measurement always causes the system to jump into an eigenstate of the dynamical variable that is being measured, the eigenvalue this eigenstate belongs to being equal to the result of the ...
3
votes
0answers
73 views

How are weak measurements taken into account in collapse models?

Collapse models have been introduced to solve the measurement problem in quantum mechanics. In collapse models the localization of wavefunction is not considered to be due to any kind of measurement ...
3
votes
2answers
458 views

Video of Double Slit Experiment Observer Effect

I have been watching a lot of videos of the double slit experiment and trying to wrap my head around it. I found examples of where the experiment has been done, however the videos cut out and only ...
12
votes
9answers
1k views

How do we know a quantum state isn't just an unknown classical state?

When an observer causes the wave function of a particle to collapse, how can we know that the wave function was not collapsed already before the measurement? Suppose we measure the z-component of the ...
3
votes
2answers
211 views

Causality in space-like separated collapse of entangled pairs

Suppose two spacelike-separated measurement events take place on an entangled pair of particles, both of which events, in isolation, would cause the entanglement to collapse. It is impossible to say ...
0
votes
1answer
129 views

What happens when we measure the particle *before* the double slit?

Like the titles states, if we measure the particle before the double slit, like right after it gets shot out, do we see an interference pattern or clump pattern on the screen after the slits?
-1
votes
2answers
171 views

Does measuring operator $A$ on state $|\psi\rangle$ leave the system in $A |\psi\rangle$?

Given an observable $A$ and a system in the state represented by the vector $|\psi \rangle$, after the measurement is the system in the state $A |\psi \rangle$?