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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Decoherence theory: System+Apparatus+Environment correlated. What becomes the global state when I measure SA? Did it collapse?

In decoherence theory, the basic situation is the following (I illustrate with two level system for simplicity). I want to measure a system $S$ by the mean of an apparatus $A$. Around it there is the ...
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Is the collapse of a classical probability density a puzzle analogous to the wave function collapse puzzle in quantum mechanics?

Famously, the collapse of the wave function is considered one of the biggest puzzles of quantum mechanics and motivates people to take ideas like the many-worlds interpretation seriously. Something ...
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Collapse of wavefunction to its eigenfunction upon measurement

In quantum mechanics, it is postulated that to every observable, we have an associated operator. It is further postulated that when we do a measurement on a system, the measured value is one of the ...
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Measuring the position of identical particles and wavefunction collapse

I'm working through Shankar's Principles of Quantum Mechanics, and I think I have hit a confusion over identical particles. The book refers to 'measuring the position' of two bosons to be $x_1$ and $...
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Different realizations of single-electron double-slit experiment

Recently I was reading about the real world realization of the double-slit experiment, in which we shoot single electrons. The final detection on the rear screen is done "by collecting the transmitted ...
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What is the probability of obtaining the same measurement a finite time after causing a wave-function collapse with my initial measurement?

Say I have a qubit that can be in two charge eigenstates, $|0\rangle$ and $|1\rangle$. The qubit also has two distinct energy levels with eigenstates $|E_0\rangle$ and $|E_1\rangle$, which each have a ...
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Is there anyway to know when the wave function collapse?

If we get 2 entangled particles and move them away from each other, is there a way to put one of them is some kind of "sensor" that would tell if the entangled particle have been measured? If yes, how ...
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Does the collapse of a state need to be necessarily included within the set of postulates of quantum mechanics?

When an operator is measured on a quantum state of a system, the state collapses into an eigenstate of the operator being measured. Should something of this sort be necessarily included within the ...
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Double slit experiment with magnetic traps [closed]

Is it possible to perform the following, modified double-slit experiment with single electrons/electron beam: The slits are separated in such a way, that each leads to a separate magnetic trap. The ...
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Can the double slit experiment be predicted in theory? [closed]

Does anyone know of the original paper (or papers) which gave the accepted theoretical derivation of the result for the double slit experiment? The issue is this: You'd think that for a screen at $x=...
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Are virtual photons observers?

Often when talking about the double-slit experiment, it is said that the wavefunction of an electron (or any other particle for that matter) collapses when observed which results in a definite ...
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Interpretation of Uncertainty After Non-ideal Measurements in QM

Answers to questions like this discuss how real measurements retain uncertainty due to limitations of our instruments. Is this uncertainty quantum or classical? If it's classical, i.e., the wave ...
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What is algebraic structure, operation or relation explains relationship between the 2 diagonal terms of the 2 density matrices?

Quantum decoherence therefore prescinds from the observer and from the measurement process in a certain way preceding it and simulating the collapse of the wave function. In particular, "...
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Definition of an “Observer” in regards to quantum physics and consciousness involvement [duplicate]

Each time I look video in regards to quantum physics there is almost always one point where they claim small matter can be represented by a wave function (can be everywhere but the item in question ...
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Does the energy and/or mass of an electron change during the act of measurement and so the wavefunction collapse?

In the double-slit experiment, if we want to know which slit did the electron go through, we have to use a laser that gives an energy to the electron. Now, I have two questions: 1. Does the energy of ...
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Quantum mechanics and the “measurement problem,” any recent advancement? [closed]

Lately, I've tried to use Google in an attempt to understand the concepts of wave function collapse and quantum decoherence. So far though, things sound a bit contradictory. If the the actual ...
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In the electron's double slits experiment, what causes the electron's wave function to collapse at the screen?

In this figure from Wikipedia, we know that electron's wavefunction collapse at screen F, causing an interference pattern. Does it mean that in this case when the wavefront arrives at the screen, the ...
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Wave function collapse without finding a particle

The wave function in Quantum Mechanics tells us, among other things, the probability of finding a particle at somme location. According to the Copenhagen interpretation of QM, when we look for and ...
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What influence has quantum-gravity on the “collapse” of a free wave-function belonging to one of many in the free quantum field?

When in Quantum Field Theory a free field has an interaction with quantum-gravity (gravitons) will this interaction has as a result that wavefunctions (or better put, one of the many) will collapse?
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Collapse of THE wave-function

Are the wave-function and the quantum field the same? If energy is in a quantum field - let's say the photon field for example. Somehow energy has been transferred from a source into the photon field....
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Bohmian vs Copenhagen Interpretation

Is there any experiment that could settle the debate between De Broglie - Bohm Pilot Wave Theory and the Copenhagen Interpretation?
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What is measurements in quantum mechanics

I really can not understand it. For instance, if a machine measures the quantum system. But no one checks this machine. Then the wave function of the quantum system is collapse or not? Besides, is ...
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Can we tell if a particle has collapsed due to a measurement?

Suppose we have two electrons A and B. My friend measure the spin on electron B the value is +1/2, and he writes on a piece of a paper the value. Electron A has not been measured, so the spin is in ...
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If I have a two-electron problem, and I measure the position of one electron. What happens to the quantum description of the other?

Suppose I have a two-electron system, and they are left alone for a long time, such that I do not know where each of them is. I then measure one electron at position $\vec r_1$. Does this collapse the ...
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What is an interaction (Quantum Mechanics) and is the wavefunction collapse an objective phenomenon?

First of all, I'm an undergrad. student of engineering physics, so I must explicit my lack of formal knowledge on the subject and total confusion with its implications. I also understand it may be ...
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Why is future 'deterministic' but not the past?

From what I saw, it seems that if theoretically you know the current states of a system (which seems impossible), you can predict its future wave function. But since there are wave function collapses, ...
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Does Quantum Entanglement have a preferred reference frame?

What I mean by this is, with wave function collapse,--and by extension, collapse between two entangled particles--being nonlocal (instantaneous across space), in what reference frame does the ...
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Is wave function collapse non-local or local?

Imagine a particle in a very large box which takes years to travel from one end to the other. Alice and Bob are outside the box, on opposing ends. Each can remove their side of the box to check if the ...
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What do quantum eraser actually do?

From what I know it basically erases which path information so even though the detectors still interact with the photon, but not able to tell which path the photon takes the result is a interference ...
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How could the momentum of a particle be directly measured in experiment?

What could be done in actual experiment to directly measure the momentum of a particle (i.e. without measuring position) in such a way that would collapse the wave function (i.e. reduce the amount of ...
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Does the anthropic principle rule out the many worlds interpretation of quantum mechanics?

TAP says that the set of observations of things we have is not a random set of all things; there is observer bias. TMWI of QM says that the universe splits to accommodate every possible collapse ...
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Quantum mechanical measurement

Suppose, a particle has non zero probability to be in any between x = 1 and x = 10. Let, we measure its position with a very low energy photon. It will collapse it’s wave function, since it disturbs ...
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The inflaton field exists in a superposition of energies. How does that affect the rate of cosmological expansion?

The inflaton field is a scalar field that each field value corresponds to different rates of expansion. The field exists in a superposition of energies, that is, the wave function hasn’t collapsed. ...
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Why hydrogen emission spectrum is discrete?

It is generally known that the emission spectrum of hydrogen is discrete, which is usually explained as follows: when a photon is emitted, the atom jumps to a lower energy eigenstate, the energy ...
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If the wavefunction of a quantum system is not an eigenfunction of some operator, how do we measure that property?

Assume we have a quantum system and its wavefunction $\psi$, but the wavefunction is not an eigenfunction of some operator (e.g. the z-component of the angular momentum $\hat{L_z}$). In this case, ...
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Practically, how does an 'observer' collapse a wave function?

I have been reading/learning about the double slit experiment, its implications in quantum theory, and how it explained that “particles” can behave as both waves and particles. I know that the wave ...
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How does the wavefunction of an electron “decollapse”?

In quantum theory, when an electron is sent through a slit (or multiple slits),the electron is described using probability amplitudes and is said to be in a superposition of multiple quantum states. ...
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Would Occam's Razor dictate adopting the Everettian interpretation of quantum mechanics? [closed]

In quantum mechanics we have the the state of a system represented entirely by a wave function, and the equation that dictates how it will evolve, i.e. the Schrodinger equation. The Copenhagen ...
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Isn't the detector always measuring, and thus always collapsing the state?

I have a radioactive particle in a box, prepared so as to initially be in a pure state $\psi_0 =1\ \theta_U+ 0\ \theta_D$ (U is Undecayed, D is Decayed). I put a Geiger counter in the box. Over ...
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Does measurement of quantum system always collapses the state of system?

Does measurement in quantum mechanics always disturb the system? The measurement postulate states that "when we do a measurement on a quantum system, the state of the system is collapsed to one of ...
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How is “the collapse postulate is also present in QFT, only hidden inside the LSZ formula?”

Background So I am reading the following here (Blog: Not Even Wrong, Blog post: Not So Spooky Action at a Distance, Commenter: vmarko) "The collapse postulate is also present in QFT, only hidden ...
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Is it possible for the measurement to yield a superposition of states in the original space?

Suppose we have a wave function $|\Psi\rangle=\sum_i c_i|\psi_i\rangle$, where the original probability probability amplitude was in a distribution of, i.e. $c_1^*c_1=\frac{1}{2},...,c_i^*c_i=\frac{1}{...
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Does the Copenhagen interpretation (+ “quasi-classical apparatus”) allow one to bypass a derivation's objection? [closed]

Background I asked this question, where I'm thinking about this joshphysics's answer: And the gist of what I get is (from the answers and the chatroom) within interpretations of quantum mechanics ...
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Wave function collapse of photon state transformed by beamsplitter

$\newcommand{\ket}[1]{\left|#1\right>}$I am trying to make sense of the math behind transforming the state of a photon with a beam splitter. Suppose I have a beamsplitter crystal which split by ...
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Does the wave function of a particle collapse if info about an observable is available in seperate chunks for many observers?

To start, I just started learning QM today so... keep that in mind. What I was trying to say is: suppose (for example) there is a box with a subatomic particle in it, the box is a 3D space so we plot ...
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Entropy of measurements; is the Von Neumann entropy lying?

Pre-measurement Let $\left| \psi \right>$ be a pure state: $$ \left| \psi \right> = a \left| 0 \right> + b \left| 1 \right> $$ The density matrix of $\left| \psi \right>$ is: $$ \...
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Penrose experiment

I just read about Penrose interpretation theory about the wave function collapse: https://en.wikipedia.org/wiki/Penrose_interpretation, which could be confirmed/infirmed by the following experiment: ...
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Sequential Double Double Slit Experiment?

Let's say you arrange the double slit experiment so that there are two sets of two slits one after the other. Like so: ...
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Which basis does the wavefunction collapse to?

When we measure position for example, how does the system "know" that we're measuring position in order to collapse to a position eigenvector? Does the wave function always evolve from the state that ...
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When does quantum entanglement cease?

On Wikipedia on Quantum entanglement: “However, this behavior gives rise to seemingly paradoxical effects: any measurement of a property of a particle performs an irreversible collapse on that ...

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