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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.

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Collapse of quantum state after measurement of degenerated eigenvalue (From textbook Shankar) (Closed)

I want to ask an easy question from Problem 4.2.1, Quantum Mechanics(2nd) by Shankar. Let's say Operators, $L_{x}$, $L_{y}$, $L_{z}$ are $$L_{x}$ = $1/2^{1/2}$ $\begin{pmatrix} 0& 1 &0 \\ ...
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Why does superposition principle and Copenhagen interpretation not contradict with themselves?

In quantum mechanics, when we say that a particle in a state $|x_1\rangle$, physically the states $|x_1 \rangle $ and $c |x_1\rangle$ (for some $c\not = 0\in \mathbb{C}$) are the same, i.e they ...
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Double slit experiment with only ONE detector [closed]

Suppose one sets up a double-slit experiment, but with only ONE detector behind one of the slits (the left one, let's say). Now suppose the dots that appear on the screen are ERASED (by the ...
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Wave particle duality and gravity

Is a particle's center of gravity at the center of its wave function or is it where we would measure the particle to be? When we measure a particle does its center of gravity shift to where the ...
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How can two electrons repel if it's impossible for free electrons to absorb or emit energy?

There is no acceptable/viable mechanism for a free electron to absorb or emit energy, without violating energy or momentum conservation. So its wavefunction cannot collapse into becoming a particle, ...
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Does the Hermitian Operator Reduce the Non-eigenstate State to the Self-Eigenstate?

Let's consider $\left| \Psi \right> $ some state of quantum system. Let's also consider some Hermitian Operator $\hat{Q}$, with the discrete specrum: $$ \hat{Q}\left| Q_n \right> = Q_n\left| ...
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Finding an energy of a particle in an infinite potential well

This question arises from a discussion I recently had with my friend. We were talking about a particle in an infinite potential well. The particle is in an arbitrary wavefunction $\Psi$. When one ...
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Does basic QM allow for superluminal “particle movement” during wavefunction collapse?

Can particles move superluminally away from their "expected values" using basic quantum theory? Here's an example: The eigenstates of a harmonic oscillator are defined from $(-\infty, \infty)$. This ...
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In the double-slit experiment of electrons (observed by photons), is it correct to say the collapse is caused by the momentum of the photons?

I'm working off the article, The Double Slit Experiment Demystified. Disproving the Quantum Consciousness connection. I think it's well-written, but I'm not convinced about this part: So what is ...
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Where is the difference to a quantum mechanic system with collapsing wavefunction in this experimental setup?

Let us have a disc throwning system, where two porcelain plates where throwning at once and in different directions, one with its axis horizontal and the other vertical. To catch ple plates we use a ...
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Difference between Wavefunction collapse and throw of dice

It might be a really stupid question and I think I am trivializing it. I am not able the understand the big issue with collapse of wave function. So we have set of probabilities and when you measure ...
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The common wavefunction and annihilation of 1 photon [closed]

QM says that if we have many particles they have a common wavefunction. Also QM says that when you measure a particle or observe it, you collapse its wavefunction. That must be a logical mistake. Now ...
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Is it certain that “experimental physics has not already detected an unexpected spontaneous collapse”

The WikiPedia page for the Ghirardi–Rimini–Weber theory states that "experimental physics has not already detected an unexpected spontaneous collapse". Is this really true? What would be the ...
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Would every particle in the universe not have some form of measurement occurring at any given time? [duplicate]

I know this is probably a common point of confusion, but I have a specific question about measurements in Quantum Mechanics. I read an explanation on this, but still have a point of confusion. The ...
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Does entangled states must become non entangled states after the measurement?

In tensor notation. A state vector $|uv\rangle$ is a tensor product(non entangled states) if and only if there is $A\in E_1(u)$ and $B\in E_2(v)$ such that $A\otimes B$. So by postulate of quantum ...
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How does the “many worlds” interpretation follow from the “universal wavefunction” idea?

So, I took this class some time ago where we discussed Hugh Everett's approach to QM. The premise seemed very logical to me: Isolated systems evolve according to the Schrödinger Equation. Of course ...
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Question regarding the projection postulate of quantum mechanics

In Quantum Mechanics, McIntyre states the projection postulate like so: After a measurement of $A$ that yields the result $a_n$, the quantum system is in a new state that is the normalized ...
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Why do we need the third axiom of QM to explain the wave function collapse? Why don't we use the decoherence process as an axiom?

I've always seen the standard interpretation and axioms of QM as in some way tricky on a philosophical level. They state the collapse of the wave function is caused by the measurement. 3.b If $A$ ...
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Does the Copenhagen interpretation really predict that Schrödinger's cat is both alive and dead?

Accoring to the Wikipedia article Schrödinger's cat, the answer is yes. I really don't think so. I don't think Schrödinger's cat is a good example because in fact, it's not the case that it will with ...
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Is it really right to say that we never measure anything exactly in QM?

In reference to this elaborate answer by @DanielSank, I would like to pose the following question(s) in order to verify my understanding of the subject matter--in particular, that of the nature of ...
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Collapse of Wavefunction, and Subsequent Time Evolution

To keep it simple, suppose the system is the well-known particle in a 1D infinite potential well. Suppose the wavefunction is $ a|1\rangle + b|2 \rangle + c|3\rangle$, where the $|i\rangle$ are ...
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Wave function collapse when it is spread over large space

Imagine there is an atom whose wavefunction is uniformly spread across a whole room. Can we estimate the time it will take for the atom interact with other atoms in the room leading to the collapse of ...
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Difference between decoherence and wave function collapse

What's the difference between The phenomenon of decoherence and the quantum wave function collapse ?
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Wave-function collapse query

A distant star emits photons towards Earth, where they can be detected and observed, however there is a very dense object (a galaxy) directly between the distant light source and our observation ...
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Collapse of the wave function and switching off measurement device before particles hit the wall detector

Would collapsing wave function by measuring/observing and then quickly turning off measurement device cause to uncollapse wave function? so it goes like this : wave--->particle---> wave(hits the wall)...
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Is there a collapse of wavefunction in scattering processes?

In the following lecture of Feynman https://youtu.be/ZcpwnozMh2U?t=16m33s a student says "we look in nature an find the first order term", referring to a particular scattering process characterised by ...
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Quantum Observation

Bear with me if I present a lack of knowledge - QM is not my field. There's a common notion in QM that until a particle is observed (measured), its properties are not definite, but rather are spread ...
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Is this assertion by Landau and Lifshitz's QM equivalent to the axiom that state spaces are vector spaces?

Many expositions of Quantum Mechanics begin by stating axioms of the following type: "The state of a quantum mechanical system is given by a nonzero vector in a complex vector (or Hilbert space) ...
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Spontaneous collapse of the universal wavefunction

How did the Hatley-Hawking wavefunction of the whole universe, as defined on the minisuperspace of all possible homogeneous and isotropic three geometries and matter fields, experience a collapse, ...
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When does the wave function collapse in the EPR paradox experiment? Shouldn't this depend on the reference frame?

Suppose you have two entangled particles. Particle A, and Particle B. If the spin of particle A is up, then the spin of particle B must be down and vice versa. Now suppose you measure the spin of A ...
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Dice roll wave function [closed]

How looks the wave function for dice roll? How to calculate probability from it? Thank you very much for help.
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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 ...
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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 ...
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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'...
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Wave function collapse, when spectrum is continuous

Is known that when measuring position the possible measurement values are eigenvalues of the position operator. Before measurement the particle is supposed to be in a physical state (wave function) ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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Measurement and normalization

Given a quantum state, we know that the act of measurement of such a state collapses it to a particular eigenspace of the operator.(For the sake of argument, let's assume the operator has a non ...
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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 +...