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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Does an entangled pair remain entangled after the first measurement?

Consider an entangled pair described by the wavefunction $$\lvert1,0\rangle = \frac{1}{\sqrt{2}}(\lvert\uparrow_1\downarrow_2\rangle-\lvert\downarrow_1\uparrow_2\rangle)$$ in in the $S_z$-basis. If ...
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Measuring momentum

I'm new here, possibly my apologies for misplacing. After a measurement in quantum mechanics, the wavefunction collapses to an eigenstate corresponding to the outcome of the measurement. Thus if we ...
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Given a collapsed state, can we derive the prior shape of the wavefunction?

More or less the title. Assume that we have found a box containing a completely isolated system of particles. We do not know for how long this system has been allowed to evolve. We do know what ...
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Why “diagonal” polarization doesn't decohere?

It is often said, that qubit should be maintained under very low temperature and kept highly isolated not to decohere. But we can represent $|0\rangle$ with vertical polarization of light and $|1\...
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Wigner's friend experiment - How is there an apparent paradox?

Wigner's friend thought experiment mentions that there is an apparent paradox - 'when exactly did the collapse occur?'. Whether it occurred when the friend made the measurement, or when Wigner asked ...
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Are combined fermion wavefunctions still antisymmetric after wavefunction collapse?

If we have two electrons in a state $|\psi\rangle=\frac{1}{\sqrt2}[|\uparrow\downarrow\rangle+|\downarrow\uparrow\rangle]$ and we measure the spin of the first electron to be up, does the wavefunction ...
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Is a brain neuron the only physical object in existence which cannot be in quantum superposition (firing / not firing)? [closed]

Is a brain neuron (actually even only my own neuron, not anybody else's) the only physical object in existence which cannot be in superposition (firing / not firing)? We never experience any ...
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Is there an experiment that verifies the quantum state collapse is a physical process or a process of reality?

Is there an experiment that verifies the quantum state collapse is a physical process or a process of reality? Or the quantum state collapse is just interpretation, but is not a physical process?
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Has it been practically proven that quantum superposition exists ? If yes, how does it even work?

I was wondering if quantum particles do actually exists in two different states simultaneously and if it has been proven they do indeed exists in a superposition of states. How has it been figured ...
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How do we prepare the electron state $|s=1/2,s_z=+1/2\rangle$ in the laboratory?

If we are interested in preparing the electron state $|+\rangle=|s=1/2,s_z=+1/2\rangle$ in the laboratory, the obvious thing is to apply a magnetic field along the positive $z$-axis (${\vec B}=B\hat{z}...
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Are humans special in that they collapse wave functions?

First of all, I don't really believe that humans are special. So I know the answer must be that they are not. But the way quantum mechanics is described is that all particles exist as clouds when ...
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Checking my understanding of 'collapsing into eigenfunctions'?

Hello could someone please check if my understanding of 'collapsing into eigenfunctions' is correct? Say we have an observable, given by a linear self-adjoint operator $A$ and then we have $\{\psi_n\}...
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What time does the particle reach the screen in this thought experiment?

Suppose a particle with a gaussian wavefunction moves to begin with towards a position detector screen. How do we obtain the 'Time of arrival' distribution, when time can't be an observable? Should ...
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Order of measurement of two observables

Let $\hat A$ and $\hat B$ be two operators representing the observables $A$ and $B$, and let $\Psi(t)$ be the state of a quantum system. Let's suppose that we measure $A$ at $t_0$ and just after that ...
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Eigenstate of position operator after collapse of the wave-function [duplicate]

I am studying basic quantum mechanics in undergrad and have hit a wall. I understand that if a measurement is made for position, the wave function collapses into one of the eigenstates of position, i....
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Collapse of the wavefunction after measurement

I learned during my study that when we make a measurement of a wavefunction then the wavefunction will collapse to one of its eigenfunctions with an eigenvalue. It is also mentioned that when we ...
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What happens in the double slit experiment if the screen is far away?

I've started reading a book on Quantum mechanics and started thinking what would happen if we did the double slit experiment with electrons but we moved the screen far far away. My newborn thought is ...
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Collapse of the wave function in non-discrete systems

Let's consider a discrete quantum system such as the harmonic oscillator or the hydrogen atom. According to quantum mechanics, when a measurement of the energy of the system is made the wave function ...
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Identifying Collapse in Wave-function [duplicate]

Is there a machine or instrument which will notify us instantly when the wave-function has collapsed if we have access to only one of the entangled particles? Note that the wave function collapse will ...
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Is there a way to detect the collapse in wave function of entangled particles instantaneously? [closed]

Is there a machine or instrument which will notify us instantly when the wave-function has collapsed if we have access to only one of the entangled particles? Note that the wave function collapse will ...
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A wave or a particle?

Ever since I first read about the quantum eraser experiment, I was wondering: if after the "measurement" the wave function collapses and we can observe a particle - does that particle remain ...
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What are some of the explanations as to why the wave function of electrons collapses when interacting with an observer?

What are some of the explanations as to why the wave function of electrons collapses when interacting with an observer? Is there a specific reason why the wave function collapses, what are some of the ...
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Are coherent states destroyed by measurements?

For a quantum harmonic oscillator in a coherent superposition, what happens if the energy is measured? Would it collapse to an energy eigenstate (a single excitation) corresponding to the result of ...
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Wave Function Collapse During Reactions

When a proton and electron combine to form Hydrogen gas after the big bang, would the wave function of the electron collapse as they bond together?
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Wave Function Collapse of an Electron

Given that if you make two observations of an electron's position in quick succession, the electron will be in the same place. Is there a time frame for how long it will stay in the same position (...
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Published claimed falsifications of objective collapse theories

My main source of information about objective collapse theories is this review article by Bassi et al. There seem to be some problems with the theory that its practitioners readily admit to, such as ...
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Problem regarding quantum entanglement and special relativity

So this question is about the strange phenomenon of quantum entanglement, or "spooky action at a distance", as Einstein called it. In particular, it's about the simplest conceivable case of ...
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Understanding superposition principle

Does the superposition principle actually tell us about our inability to predict what happens during the course of the experiment? Does it tell that, since an experiment has multiple outcomes ( i.e , ...
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Wave function collapse for experimental quantum state preparation

Has the John von Neumann projection, or the wave function collapse, been used in the experimental preparation of quantum states? As an illustration, for a pair of EPR-type entangled 2-level atoms $$|\...
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How does the apparatus in QM cause the interruption of the interference pattern in the Pilot-Wave theory?

In the wikipedia page, it is written that the apparent collapse of the wave function in the Pilot-Wave theory happens because "the environment registering the detection effectively separates the ...
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Can a particle stop disintegrating by zeno effect? [duplicate]

Can a free neutron be prevented from disintegrating by observing it continuously? (Zeno effect).
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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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How was the double slit experiment predicted in theory? [closed]

I am interested to know how theorists made predictions for the double slit experiment. The issue is this: You'd think that for a screen at $x=L$, the interference pattern is given by $|\psi(x=L,t)|^2$....
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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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Is quantum-gravity able to let a quantum field associated with one particle collapse to one eigenstate?

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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