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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What's the difference between the Copenhagen and many-worlds interpretations?

I don't know that much about quantum mechanics, but after reading the Wikipedia pages for the Copenhagen and many-worlds interpretations, I'm left with the impression that the two are describing the ...
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Wave function collapse violates causality?

I have read this question: Does photon interference violate causality? where S.Mcgrew says: Edit 8/10/18 Bottom line: you're right that wave function collapse violates the principle of ...
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Will there be two cats in the box (superposition) if I use virtual particles (magnetic field) to open the box in Schrodinger's experiment?

I have read this question: How does a Wavefunction collapse? Where annav says: More specifically, what conditions cause a wavefunction for a quantum particle to collapse? A ...
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Would the first consciousness uploaded be able to cause a wave collapse? [closed]

If he/she had a camera connected to their local computer and he/she were the only ones with access to the double slit experiment results. If the results would show interference ..would that imply he/...
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Double sit experiment and Uncertainty

If we try to an electron with a high energy photon, we precisely detect its position, while its momentum becomes totally uncertain. On the other hand, if we detect it using a low energy photon, its ...
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Doesn't gravity collapse superposition? [duplicate]

Correct me if I'm wrong, but if you have a proton that is in superposition, you don't know where exactly it is; it is everywhere but with different probability. Couldn't you measure the gravity field ...
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Effects of measurement on particle energy

According to quantum mechanics, once you measure a particle's energy, its wave function collapse into some state, an eigenfunction with some eigenvalue (which is the particle energy). But if a ...
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Why does the electron wavefunction not collapse within atoms at room temperature in gas, liquids or solids due to decoherence?

Decoherence theory predicts that any quantum particle coupled to any "large" environment should undergo decoherence and its wavefunction should collapse. This explains why measurement leads to ...
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Wave function. Measurement of the absence

Imagine we have a particle in an eigenstate of a Hamiltonian, as time passes it will remain in that state. We suppose in this question that the position can take a continuum of values. If we measure ...
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Wavefunction collapse in Stern-Gerlach experiment

Consider silver atoms coming from an S(X) apparatus, after S(X) apparatus we place an S(Z) apparatus $$ |\mathrm{SX+}\rangle= \frac{1}{2}|\mathrm{SZ+}\rangle + \frac{1}{2}|\mathrm{SZ-}\rangle, $$ ...
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Wave function collapse and a general wave function

Action of an operator on a state vector collapses the wave function to any of the eigenstate of that operator , So we get resulting state of the system as some base ket. But mathematically action of ...
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How to understand the transition amplitude in the Copenhagen interpretation

In Chapter 8 of Townsend's A Modern Approach to Quantum Mechanics, he states that the expression $\langle x', t' | x_0, t_0 \rangle$ gives the amplitude for a particle that is at position $x_0$ to at ...
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How do we know which states are decohered by the environment?

If I take an atom in a momentum eigenstate, or just a very narrow gaussian in momentum space (with a very large spread in position space), and then I throw it into a gas, it will quickly decohere into ...
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Can wave collapse during measurement be avoided with a better experiment / measurement apparatus?

Or to restate the question, does quantum mechanics or the quantum field theory state or imply that we can only observe the wave in a collapsed state? And if they don't, do we have any promising ...
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Does measurement of momentum always collapse the wave function into a plane wave?

When you measure $\vec p$ the wave function collapses to an eigenstate of the momentum operator. These eigenfunctions are always plane waves, correct? Does it mean that momentum always collapses into ...
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Doubt about the probabilistic nature of quantum stuff and the field theory

To the quantum field theory, is it like there's "two layers of reality", one in which things are just probabilities waves that collapses into the quantum fields or is the quantum field and its waves ...
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Does Quantum Entanglement happen between two wavefunctions? [closed]

Does the entanglement happen between two particles or two wavefunctions? If it's wavefunction then what happens to the two wavefuntions after getting entangled?
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Why is wave-function collapse still being taught in quantum mechanics? [closed]

I don't really understand why wave-function collapse is still being taught while we seem to have better interpretations of QM available nowadays. During the early development of quantum mechanics the ...
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Why doesn't observing a photon collapse it's wave function into a B or W3 boson?

According to electroweak theory, the photon ($\gamma^0$) and weak bosons ($W^+, W^-, Z^0$) are all linear combinations or superpositions of the weak hypercharge boson ($B$) and the weak isospin bosons ...
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Annihilation Operator on Entangled State - How Does This Not Break No-Communication Theorem?

If I have the state $$|\psi\rangle=\frac{1}{\sqrt{2}}\left(|2\rangle_{A}|0\rangle_{B}+|0\rangle_{A}|2\rangle_{B}\right)$$ and apply the annihilation operator to B $$a_{B}|\psi\rangle=|\phi\rangle=\...
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Could we interpret search for the Pitch as a process similar to the collapse of the wave function?

According to Wikipedia: In quantum mechanics, wave function collapse is said to occur when a wave function—initially in a superposition of several eigenstates—appears to reduce to a single eigenstate ...
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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’s use a disc throwning system, where two porcelain plates are thrown at once and in different directions, one with its axis horizontal and the other vertical. To catch the plates we use a detector,...
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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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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, ...