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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Continuous Collapse Interpretation

Suppose we interpret quantum mechanics to mean that the collapse randomly happens at every single moment. Wouldn't this be identical to the many worlds interpretation except much less objectional ...
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Does quantum tunneling result in the collapse of the wave function?

Does quantum tunneling itself result in the collapse of the quantum object's wave function? So, as a hypothetical scenario, suppose you have a two-slit experiment, but instead of two slits, you have ...
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Is somebody familiar with the Continuous Spontaneous Localization (CSL) model of collapse? Is this model trustable?

The Continuous Spontaneous Localization (CSL) model of collapse was originally invented by Ghirardi, Rimini Weber and Pearle. This model tries to mimic the wave-function collapse. But is it trustable? ...
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Does information disappear when a wavefunction collapses?

The wavefunction of a particle evolves with time in a manner strictly defined by the Schrodinger equation and the local environment. The wavefunction can become very complicated (e.g. a photon trapped ...
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Wavefunction superposition state

Before measurement the wavefunction of a quantum particle, eg an electron, evolves in a superposition state. Can the following wavefunction $$\Psi = 1\,\,\lvert \uparrow \rangle + 0 \,\,\lvert \...
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Are non-linear extensions to QM equivalent to time travel?

I recently learned of the existence of Objective Collapse theories which add non-linear terms to QM to explain wave function collapse. Per the 2014 paper Treating Time Travel Quantum Mechanically, the ...
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Collapse of state vector for degenerate eigenvalues

Consider a state vector given by $$|\psi\rangle=a|w_1\rangle + b|w_2\rangle+c|w_3\rangle$$ where $|w_1\rangle,|w_2\rangle$ and $ |w_3\rangle$ are orthonormal eigenstates of an observable operator $\...
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Can observation by animals collapse the wave function?

In Schrodinger's cat, somehow the cat is dead and alive at the same time until someone opens the box, observes that cat's state, and collapses the wave function. Of course, something can't be dead and ...
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Does a wave function not collapse upon detection?

In Sabine Hossenfelder’s YouTube video “The Delayed Choice Quantum Eraser, Debunked”, she states that even if you detect which slit the wave function goes through (in the double-slit experiment) then ...
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The Copenhagen Interpretation

What are the actual papers in which Bohr, Born, and others proposed the Copenhagen interpretation? I know that Bohr himself didn't use the term, but I assume that he outlined the way of understanding ...
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Why macroscopic bodies should exist as wavepacket?

Based on my understanding, we assume that the electrons, exist as wavepackets in the solids while deriving the transport equations for transistors, we create wavepackets out of momentum eigenstates ...
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Two questions regarding the quantum mechanical wavefunction

I'm just starting with quantum mechanics and I've got some questions. Long after measurement of a position of a particle, does the wavefunction return to the same form, or does an entirely different ...
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Projection postulate and the state of a system

Quantum Mechanics, McIntyre states the projection postulate as: After a measurement of $A$ that yields the result $a_n$, the quantum system is in a new state that is the normalized projection of the ...
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Can one photon excite two widely-spaced atoms simultaneously?

For example, can a single 1 eV photon excite 0.5 eV transitions in both of two atoms that are widely separated (events outside each other's light-cones)? In order to excite a transition, the incoming ...
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Does wavefunction collapses near event horizon? [closed]

Picture an electron falling into an event horizon, so far from what I read gravity is either not a force or it is extremely weak therefore it doesn't cause wavefunction to collapse unless the strength ...
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Why are wavefunction collapses instantaneous?

From my understanding of quantum mechanics, when a wavefunction is observed, it collapses into a single state instantaneously (or at least in the length of a Planck time.) Is there a reason it has to ...
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Will the wave function of an electron in a wire (or atom) collapse under magnetic interaction?

The wave function of a particle is interpreted as a probability distribution. If the particle interacts, the wave function will usually collapse, and the particle will manifest it self at a specific ...
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Have objective collapse theories been ruled out by recent experiments?

Have objective collapse theories been ruled out by recent experiments, such as the entanglement of macroscopic objects? (vibrating drumheads)
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Problems with Schrödinger's cat

I wanted to check my understanding of why exactly the whole "cat in a superposition of alive-and-dead" would never actually happen in the situation described in the Schrödinger's cat thought ...
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I don't understand Wigner's friend paradox

The Wigner's friend experiment goes like this: Say Wigner instructed his friend to perform Schrödinger's cat experiment in a laboratory while he work from home, his friend made the measurement and ...
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Do probability wave function moves or it is just sitting there until it interacts?

Imagine an electron is emitted from a source, at this moment the probability wave function of the electron appears... then how come the same electron have to take some time to reach the target such as ...
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In Stern-Gerlach experiment, where does wavefunction collapse?

I was reading Sakurai's Modern QM and it talks about Stern-Gerlach experiment in chapter 1. As silver atom passes through non-uniform magnetic field and enters detector downstream, a measurement is ...
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The wave function collapse and uncertainty principle [duplicate]

If we measure the position of a quantum mechanical particle, then, according to the postulates, the particle's wave function collapses into a delta function and the measured result is one of the ...
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If quantum particles are always waves, then what are we really measuring the position, angular momentum, spin etc. of?

I've been losing sleep trying to marry, in the usual QM formulation we've been learning, what my lecturer said in our problems class a few weeks back - 'quantum particles are never particles (in the ...
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Can momentum be measured from a single, non-collapsed wavefunction?

Let's consider a one particle free wavefunction (WF). A WF evolves in time over space. The WF in momentum space does the same in momentum space, but "contrarily" (it's a Fourier transform of ...
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Why does quantum physics use "observation" rather than "interaction" as the term for the trigger which collapses the wave function?

So I understand that when talking about quantum mechanics, quantum entities are assumed to exist as a probability wave, until they are "observed", which collapses the wave function into an ...
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Is the collapse of the wavefunction a contradiction of special relativity?

During the collapse of the wavefunction, the electron density spread over million of miles gets concentrated in very small region in literally no time. This means that electron density travels at ...
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Is the wave-function collapse real or an interpretation? [closed]

Consider the double slit experiment in which the position of the particle is in a superposition of the 'eigenfunctions' of the position operator before they reach the detector. This process is ...
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Superposition of particle positions

There is an interesting analogy given in this video (beginning at 12:20 -- link jumps directly to this timestamp) on Quantum Field Theory which I am trying to reconcile with one or more ...
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A particle in a box is measured to not be on the right hand side of the box. How does the wave function collapse?

Starting with initial wave function of a particle in a box with width $2\pi$. We look for the particle in the right half of the box but do not find it there. Does the wave function collapse to the ...
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Wave function collapse as a limit (classical/thermodynamic/macroscopic?)

It seems to me, it should be possible to model the wave function collapse by describing the macroscopic object (i.e., the measurement device) in purely quantum terms and then taking the classical ...
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I'm not seeing any measurement/wave function collapse issue in quantum mechanics

The information about a particle is contained in a vector of unit-norm called the wave function. One postulates says that this wave function is supposed to evolve with time as the particle interacts ...
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Does the collapse of the wave function depend on the observer?

Reading various articles on quantum physics paradoxes, I found the following interesting statement: When a measurement is carried out inside of a closed lab, such a measurement leads to a collapse ...
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In objective collapse theory, do large objects constantly collapse?

In objective collapse theory, do large objects constantly collapse? So I understood it like this: Wave collapses into one concentrated point, Wave spreads out, Wave collapses into one concentrated ...
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Wavefunction Collapse of a Degenerate System with a Finite Range Measurement

A particle, at time $t=T$, has the following wavefunction: $\left| \psi \right> =\frac { 1 }{ \sqrt { 4 } } \left( \left| A \right> \left| - \right> +\left| B \right> \left| + \right> ...
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Could the quantum wave function collapse under these settings?

I am wondering if this type of experiment been done. You observe the phenomenon either by the usual double slit exeprimenet and by delayed choice experiment. You record the which way path as usual. ...
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How can the collapse of the wavefunction be compatible with Heisenberg uncertainty principle?

Consider the position wavefunction $|Ψ\rangle$, which can be written as a linear combination of the eigenstates $|Ψ_n\rangle$ of the position operator: $$|Ψ\rangle = c_1|Ψ_1\rangle + c_2|Ψ_2\rangle + ....
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Does an electron have multiple positions BEFORE being observed?

I realize that an electron can only ever be detected at a single location in space when it is observed. That is, post-detection, an electron can only ever be at a single position in space. But prior ...
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Is time the collapse of quantum superposition across the universe?

Just to preface, I admit I'm not a physicist, or even well-read on science-related things (though I do read articles from various aggregate sites and sometimes purchase New Scientist) but I am ...
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How does the precision of the measuring device affect the wave function we get instantly after a measurement on $\Psi$?

Going through David J. Griffiths' Quantum Mechanics book today, I read the following: If the operator $Q(\hat x,-i\hbar\ \partial_x)$ has a continous spectrum with eigenvector $f_y(x)$ corresponding ...
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Will the Hilbert space get expanded when measuring the entangled state?

If I have two electrons that are indistinguishable, as I understand, they are entangled. And the Hilbert space that describes the behavior of this pair of electrons is a subspace of the Tensor product ...
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When will a wave function collapse if the observer was only a camera and the video was watched later in time?

If the only observer for the Schrödinger's cat experiment was a camera filming the box from the outside while the box was opened automatically without direct human intervention, and the only ...
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How is the wavefunction collapse related to the application of that operator on a state?

I am following Griffith's Introduction to Quantum Mechanics, and after proving that $$\sigma _A ^2 \sigma _B ^2 \geq \left( \frac{1}{2i} \langle [A,B]\rangle \right)$$ he says You can certainly ...
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Has there been experimental evidence that entangled state collapses simultaneously?

If we observe the observable of one particle among two particles which are entangled each other and separated far away, we can determine the value of the other particle’s same observable from the ...
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Position of the wavefunction's collapse

When a wave function is said to "collapse" to a single point during a measurement, is there uncertainty about the point's position or is it known infinitely precisely?
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Can Einstein's action at a distance be action into the past?

This youtube video is about how it is not measurable or of any consequence what the one way speed of light is, only that a two way trip has an average speed of $c$. An example is moving ...
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Whose state (or wavefunction) changes (or collapses) upon observation: System's or Observer's?

I was learning about Qubit measurement and the basics of Quantum computing. The instructor forced a lot on the following statement : Assume an isolated system S. Let an observer O interact with the ...
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What would one see, if they looked at a system in energy eigenstate?

We know, time evolution of energy eigenstates is extremely simple $\psi(t)=\psi(0)e^{-iEt}$. On the other hand we have symmetry breaking. Here I present an interesting thought experiment, and wonder ...
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What problem is the Many-Worlds Interpretation actually solving? Is it a reframing of the measurement problem?

Before I state my question I want to say I am in no way an expert/professional in this field. I read quite a bit on the subject and I consider myself familiar with the basic concepts but I really want ...
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Testing objective vs. subjective collapse for double slit

Suppose we have double-slit experiment. Before the right slit, we add a particle detector that allows the particle to go through. It is well-known that if we carry this out, then the wave ...
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