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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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Was Einstein "spooky action at a distance" about entanglement or about wave function collapse?

I've been watching Sabine's videos and this is my understanding: There is no "spooky action at a distance" based simply on entanglement. Entanglement is a correlation. There is no ...
Ray Wood's user avatar
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Collapse of wavefunction [duplicate]

Why do the wavefunction always collapse at a single point always when position is measured?
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In entanglement, does the measurement of one particle collapse the joint wave function or not?

I’m having trouble understanding what exactly happens when one makes a measurement on one particle, especially since I am seeing conflicting information on here, on Wikipedia, and from other sources. ...
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Finding literature with quantum tomography during a measurement to "see" the wave function collapse

I was at a journal club some time around 2020 where we discussed a paper that I am trying to find again. The claim was that it had experimentally shown that wave function collapse was not "...
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Relationship of the do-operator in do calculus and the notion of the collapse of wave a function

I stumbled over the "do calculus" in causal modeling https://arxiv.org/abs/1210.4852 and the do-operator which is defined in this post https://stats.stackexchange.com/a/643333/298651 The do-...
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Is there a limit to the number of observers to a wireless broadcast due to quantum mechanics?

My question seems obvious but nobody is talking about it. The way I understand it, an electromagnetic wave collapses to a particle when observed. This goes for electrons and photons but I imagine the ...
average_coder's user avatar
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1 answer
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What will be wave function after application of operator?

In the mathematical treatment of quantum mechanics, we have a wave function ($ψ$) that helps us to know the different information (like position, velocity, energy, etc.). To measure such a quantity we ...
roshannepal_x's user avatar
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Is the collapse of the wavefunction relativistic?

If a stationary observer, 'A', observes the collapse of a wavefunction, does an observer, 'B', traveling at relativistic speed observe a different collapse of the same wavefunction? What do all the ...
Marco Fabbri's user avatar
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Would quantum superposition stop if we observe the particle in the case of photosynthesis?

I started looking up more into quantum biology from photosynthesis to genetics mutation and how they are explained by quantum properties. my question is about the case of photosynthesis: quantum ...
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Collapse of Quantum State and Coefficients

I have found the following exercise in one of my problem sheets: Suppose we have an observable $Q$ and its corresponding operator $\hat{Q}$ has three eigenfunctions $\varphi_1, \varphi_2, \varphi_3$ ...
Marçal's user avatar
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Measurement values affects probabilities in QM?

Consider a non-degenerate operator $\Omega$ with discrete eigenvalues $\omega_i$, where $i=1,2,3,...$. We can write $\Omega = \sum_i \omega_i~|\omega_i\rangle \langle \omega_i|$, where $|\omega_i\...
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Does a quantum measurement change the state in the past? [closed]

Consider the following very basic quantum mechanics experiment. At time $t_0$, a system $S$ is in superposition of two orthogonal states $|A\rangle$ and $|B\rangle$, which we could describe by $\frac{...
Riemann's user avatar
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Shouldn't any measurement cause all wavefunctions to collapse?

Given the fact that every wavefunction exists everywhere in space, shouldn't a measurement at any location cause all wave functions to collapse since a measurement at any point measures all ...
Chris Laforet's user avatar
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Doesn't the Copenhagen Interpretation violate the Second Law of Thermodynamics? [closed]

It feels like the transition from a sea of probability of a droplet of precision (or wave, depending what you're looking for) would be a loss of entropy, if so wouldn't this violate the Second Law? Or ...
Leo's Lizard's user avatar
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Can the collapse of the wave function be modelled as a quantum system on its own?

Imagine I have an observer $\mathcal O$, a quantum system $\mathcal S$ with Hilbert space $V_{\mathcal S}$, a Hamiltonian $H$, a self-adjoint operator $A$ acting on $V_{\mathcal S}$. The system is in ...
Lorenzo Pompili's user avatar
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Do objective collapse equations actually collapse the state?

Why are objective collapse theories stated to collapse the state from a superposition to a single eigenstate (corresponding to the measured eigenvalue)? For this discussion, we are focusing on the ...
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Quantum Collapse during the Measurement of the spectrum of hydrogen [closed]

We have hydrogen inside a tube, and we induce a voltage on it; a current passes through it and light is emitted. The frequencies of light correspond to the differences of the eigenvalues of the energy ...
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Gravity cause wavefunction collapse? (Roger penrose) [closed]

Roger Penrose suggested that gravity might play a role in the collapse of the wave function (which describes a system as a superposition of multiple values of Position, momentum etc.). According to ...
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FTL communication setup. Why wouldn't this work?

The setup is similar to quantum eraser experiments (see below). The laser pulses at regular intervals to send bunches of photons. They get split in half as entangled particles. One beam is sent 1 ...
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Double slit experiment with detector and experimenter

In the double slit experiment we have particles which travel through two slits and then hit a final wall/detector. We can perform the experiment with or without an extra detector at the slits which ...
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Spin state coefficients in Stern-Gerlach experiment

I'm trying to learn quantum mechanics basics by myself. I've been working on the Stern-Gerlach experiment. Now, positioning two apparatus both along the same direction (first z, then x and y) it is ...
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Is wave function measurable?

I apologize for the length of this naive question. I am not sure it is appropriate for this community. Is wave function measurable? This is really a question in Atomic and Molecular Optics. I hear ...
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Is the superposition of a particle before the collapse of the wave function a relative effect?

From the perspective of an electron in the double slit experiment, does the "rest of the universe" that it is disconnected from behave in the same manner as the electron does in our view? As ...
Helena's user avatar
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How can a system be in superposition when there’s a force associated with it?

Not sure what the best way to word the title would be but I’ll explain further: suppose we’re talking about the double slit experiment. As the electron moves its electric field changes, which exerts a ...
user62783's user avatar
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Wave functions of valence and conduction electron

I read that the standard depiction of covalent bonding is misleading. It gives the impression that the valence electron exists at that bond site. But really it exists as a wave throughout the crystal. ...
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What happens to the wave function after it collapses?

If a quantum particle is described by a certain wave function and we express it as superposition of for example its possibles energy states, after we measure it the wave function collapses and we ...
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Do the results of the Elitzur-Vaidman quantum bomb tester experiment imply that counterfactual events affect what is observed?

Assuming that light travels as photons that can interfere with themselves while also only being detected as specific localized points, the results of the Elitzur-Vaidman quantum bomb tester experiment ...
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Does collapse in different basis change probabilities differently?

Consider two quantum systems, with two associated Hilbert spaces $H_1, H_2$ and corresponding algebra of observables. Consider an entangled joint state of the two systems. In general it will be ...
Pol's user avatar
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Physicality of post-measurement description of a state based on information of measurement outcomes

Say, we find two exact systems in a pure state. When Alice does von Neumann measurement on it, the state collapse to a pure state because Alice knows the measurement outcomes. In this case, we have $\...
Pratham Hullamballi's user avatar
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4 answers
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Is signal photon independent of idler photon in Delayed Choice Quantum Eraser?

--Diagram from Wikipedia of the experiment of Kim et al. (1999) Original research paper: A Delayed Choice Quantum Eraser I want to know whether the landing position of the signal photon (photon that ...
Duke William's user avatar
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2 answers
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In the double slit experiment, when emitting one photon at a time, why don't all of them travel the same path?

If we fire one photon at a time, why don't all of the photons hit the barrier exactly in between the two slits? How come each photon goes in different directions? (some go through top slit, some go ...
Fuad's user avatar
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Copenhagen Interpretation vs Quantum Decoherence? [closed]

I'm learning about Quantum Mechanics, and have a question about the Copenhagen Interpretation. It states that the act of observation collapses the wave function. It seems many people take this to ...
MajorChipHazard's user avatar
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2 answers
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What happen to the electromagnetic waves when a photon's "wave function" collapses?

We interpret the electron's wave function as a probabilistic wave function. During a measurement, it has the probability to collapse to any of the eigenstates of the measurement operator based on the ...
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Does the wave function collapse cause a high probability current?

If you perform a measurement the wavefunction collapses to a certain position. Does this mean there is a very high probability current to that position? Comparable to an strong electrical current ...
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Is collapse of wavefunction actually relative?

I suddenly had an odd philosophical question. Suppose there are two people and the Schrodinger's cat experiment is done, such that after placing the dynamite and cat within the box and waiting for a ...
Solid - NMR's user avatar
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1 answer
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Wavefunction collapse in a bubble chamber

When a particle enters a bubble chamber, its wavefunction collapses and the particle behaves as a classical one. Is it correct?
Andreas Valadakis's user avatar
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1 answer
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The many-worlds interpretation and a free particle

How does the many-worlds interpretation understand the time evolution and spread of a free particle wave function? That is, does every continuously small change constitute a cosmic action that causes ...
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Is there an axiom for degenerate (or continuous) quantum collapse? [duplicate]

Most introductory QM texts say that measurement collapses the quantum state into one of the eigenstates of the observable's operator (and with a probability amplitude given by the corresponding ...
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Collapse postulate in the density operator formalism [duplicate]

To the extent that the collapse postulate holds, textbooks will almost invariably restrict the discussion to contexts in which states are represented by normalized kets, so that the collapse postulate ...
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Does the wave function of system plus detector satisfy the Schrödinger equation?

Let $S$ be a quantum system and let $D$ be a detector. Suppose that $D+S$ does not interact with the environment. Now when $D$ makes a measurement of $S$, the wave function of $S$ collapses. Therefore,...
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Is a quantum measurement a unitary transformation of the entire system? [duplicate]

When we measure a quantum particle, its wavefunction collapses to an eigenstate. This is not a unitary transformation. However, measuring a particle neccesarily involves the particle interacting with ...
Riemann's user avatar
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3 answers
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Is the measurement problem an interpretation or practical problem?

According to Wikipedia: In quantum mechanics, the measurement problem is the problem of how, or whether, wave function collapse occurs. Is the measurement problem an interpretation problem or a ...
Riemann's user avatar
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2 votes
3 answers
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Can gravity cause a wave function to collapse?

Assume the Copenhagen interpretation. Suppose that a particle, for example an electron, has a wavefunction. If a heavy object, like the Earth, is close by, then that object interacts with the electron ...
Riemann's user avatar
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How much does the collapse of the wave function reveal about the state of the quantum prior to collapse?

The best way I can pose this question is through an example: suppose a photon passes through a beamsplitter, putting the photon into a superposition of the two paths (reflected or passed through), and ...
OneStrangeQuark's user avatar
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1 answer
401 views

Does an electron's wave function collapse when it emits a photon?

I've been wondering how electromagnetic interactions between electrons are calculated if the position isn't determined until the wavefunction describing position collapses. Does the wavefunction need ...
Iron Attorney's user avatar
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1 answer
66 views

Quantum wave function collapse by unknown observer [closed]

If there's an "unknown" third-party observer of a particle, that would collapse the wave function for the first party, but has that "ever" happened, without knowing who the ...
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2 answers
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Double slit question - wavefunction collapse

If we fire photons at the double slit, we see an interference pattern on the screen. We know that if a quantum system interacts with any outside object (such as a detector, etc), its wavefunction ...
Irina Samsonova's user avatar
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1 answer
124 views

Where no observer exists, does this mean the wavefunction never collapses?

In most places across the universe, there is no conceivably sentient candidate to act as an "observer" to this system. Are we to believe that, in the emptiness of intergalactic space, or ...
James's user avatar
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1 answer
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Who caused first collapse of wave function?

With my wife we discuss a quantum theory and wonder whether a wave function could collapse without an observer - meaning a human/or any other living beings. If so we could make a conclusion that there ...
Jirka Meluzin's user avatar
3 votes
4 answers
534 views

Meaning of eigenvalue of the position operator $\hat{x}$?

Apologies for asking a question which may be too basic. I understand at the conceptual level that a measurement collapses a wavefunction into a single spike, which will then evolve again immediately ...
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