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 happens when we measure the particle *before* the double slit?

Like the titles states, if we measure the particle before the double slit, like right after it gets shot out, do we see an interference pattern or clump pattern on the screen after the slits?
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Does measuring operator $A$ on state $|\psi\rangle$ leave the system in $A |\psi\rangle$?

Given an observable $A$ and a system in the state represented by the vector $|\psi \rangle$, after the measurement is the system in the state $A |\psi \rangle$?
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Measurement of position of particle

Say a particle was found to be at $C$. If I measure the position of particle immediately, its given in Griffith's book that it will still be at $C$. In the macroscopic world, isnt this true only if ...
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Does collapse of wave function to a momentum eigenstate violate speed of light restriction?

Let's consider a free system where the Hamiltonian is $\hat{p}^2/2m$. At time $t=0$, we start with a state at position $x$. An instantaneous time $\delta t$ later, where $\delta t\rightarrow 0$, we ...
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Collapse of wave function

Suppose a quantum system is initially at a state $\psi_0$ and that a measurement of an observable $f$ is performed. Immediately after the measurement, the system will be in a state that is an ...
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Can you detect when wave function collapse occurs?

Not literally when as in the moment it occurs, but if you're given a series of particles can you differentiate between the particles which have been collapsed and those that have not? If you have a ...
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202 views

Does a Polarizing Beam Splitter Cause Wave Function Collapse?

For a single photon, its polarization can be a superposition of two orthogonal bases (e.g. horizontal or vertical). However, as I understand, once it has been measured, it must collapse into one of ...
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120 views

Collapse of Wavefunction after space-like Seperated Measurements

Suppose I have a pair of entangled particles, each one goes in a different direction. Now I measure the momentum of one particle and the position of the other at the same time. Because the ...
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Double slit experiment; evidence of wavefunction collapse

This video shows the change of a photon's interference pattern in real time of the Young's single and double slit experiment. In this video it is claimed that by adding a detector to view how the ...
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Is wavefunction collapse “global”?

I have the feeling that the premises of this question may not be coherent (so to speak), but here goes: Suppose we have a system $X$ in a quantum superposition between states $0$ and $1$, say, with ...
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Wavefunction Collapse

I believe my Lecturer and the textbook have contradicted one another. My lecturer gave the example that if the spatial part of the wavefunction of a particle is given by $\psi(x) = c_1\psi_1(x) + c_2\...
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Linear Combinations of Energy Eigenfunctions in 1D

Given that a particle is in a state defined by the wavefunction: $$\Psi (x,t) = \psi_0(x)e^{-iE_0t/\hbar}+\psi_1(x)e^{-iE_1t/\hbar}$$ where $\psi_0(x)$ and $\psi_1(x)$ are the energy eigenfunctions of ...
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Given any two quantum states and the information that the system is in one of these two states

Given any two quantum states and the information that the system is in one of these two states, one cannot reliably devise a single measurement which could determine with certainty which state the ...
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Precedence and quantum entanglement: The Alain Aspect experiment in spacetime

Recall that the spin components of a spin-entangled pair do not exist until one of the pair undergoes quantum observation, at which time both of the pair immediately obtain quantum random opposing ...
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2answers
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How does really the “wave function collapse” work? [closed]

It's usually said that "the direct observation of a process makes the wave function of the system to collapse". How does really that process happen? What exactly means for a wave function to collapse?...
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Understanding wave functions of matter waves

The wave functions of matter waves give the probability density of the particle being at a certain location. Does this arise because as an outside observer, we have incomplete information about the ...
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Successor to Copenhagen Interpretation as Orthodox Interpreation of Quantum Mechanics

First, I read the questions FAQ for this and I hope this does not violate the rules. I am not asking for personal opinion, but for observations of hard evidence of trends on this subject. When I ...
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Quantum eraser experiment with unbalanced interfereometers

In quantum eraser experiments, which path information is made available and then destroyed before the photon hits the screen. Now, say we had an experiment in which a photon is sent to a double slit ...
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Current quantum theory of interference

I have always thought that the quantum theory states that interference occurs when photons behave like waves and two or more possible paths exist. Interference can then be destroyed if the path of the ...
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Operator and apparatus in quantum mechanics? [closed]

If $L$ is an Hermitian matrix associated with an apparatus acting on state $\Psi$, how does the state vector $\Psi$ collapse or change according to matrix arithmetic?
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Wave Function Collapse and Which Path Information

From what I understand, wave function collapse occurs when a photon/wave/particle/whatevertheheckitis which was previously in a superposition of states, collapses to one state. Now, in a double slit ...
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Quantum double slit which-way problem

I recall reading that if you put a parallel polarizing filter over one slit and a perpendicularly polarizing filter over the other slit, and send a singe photon to the slits, then there is no ...
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787 views

What exactly causes quantum wave function collapse? [duplicate]

I've heard many things, such as the wave function collapses when the particle or system it determines is observed. But then I've heard that if we consider that to be the case, it's incomplete. What ...
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Wave function collapse and Schrodinger's equation without measurement

Will wave function collapse without measurement? Since all matters are described by wave functions, then in principle, I should be able to describe wave function collapse by Schrodinger's equation. (...
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What would be the abilities of a wave function collapsing oracle? [closed]

Although the Bell's theorem dismiss local hidden variables as an explanation of the quantum variability, there is nothing to prevent an observer to see the occurrence of a wave function collapse as ...
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Is the collapsed wavefunction a solution of Time-dependent Schrodinger equation?

For measurement of any observable associated with the particle, should the wavefunction after collapse be a solution of the time-dependent Schrodinger equation? A general solution of the time ...
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423 views

Measurement of position after collapse of a wavefunction

Suppose I have a wavefunction which collapses to a certain eigenstate after a measurement of energy. In that state, I perform a calculation of position and obtain a certain position value, say $x_0$. ...
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162 views

Wave Function State Reduction As a Result of Quantum Measurement

This is a question about indirect quantum measurement, involving an observable of an object of interest and a probe that is used to measure that observable. In this experiment, an observable of the ...
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If Alice is moving at relatavistic speeds compared to Bob, is collapse still simultaneous?

I have read some papers about experimental proof of non-locality involving a laser that goes through a beam-splitter and then each "half" goes to an observer (traditionally "Alice" and "Bob"). It has ...
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73 views

Collapsing a wave function without hitting the detector

If a free particle is placed at the origin (in 1D) with a wave function that consists of a superposition of the particle moving in both the +/- X direction, and a single detector is placed on the ...
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2answers
230 views

Wavefunction collapse and relativity [closed]

In classical QM, when I measure the wave function of a system, e.g. the position of an electron somewhere in a box, its wave function collapses instantaneously to some classical position. But how fast ...
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What are the exact setups to observe a wave function and its collapsed state?

I was reading this article: http://io9.com/5528321/how-smart-do-you-need-to-be-to-collapse-a-wave-function and I need some clarification on the experiment setup. My current understanding is that if ...
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Has the double-slit experiment been performed with animals as the observers?

As the title says, has the double-slit experiment been performed with animals (not humans) as the observers? If yes, which animal was used and what was the result?
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At what point do quantum wave functions collapse? [duplicate]

At what point do quantum wave functions collapse? Let me give you two examples to make that question more clear: Let us think of the double slit experiment. We humans see the light at certain ...
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Can the Born rule be derived? [duplicate]

$\renewcommand{ket}[1]{|#1\rangle}$ If we have a particle and we know the initial state $|\psi\rangle$ of everything that is relevant, and we know the full Hamiltonian $H$, then we should be able to ...
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What state the wave function collapses into after an inaccurate measurement?

I'm watching MIT online lectures Quantum Physics I (roughly from one hour mark in the video). The lecturer explains wave functions that describe "Stationary States" that consist of a single energy ...
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5answers
667 views

Does measurement change the evolution of wave function?

Basically any measurement is on wave function $|\psi\rangle$ is done by operator $X$ such that $X|\psi\rangle$ results observable $x$ with some probability. But what happens to $|\psi\rangle$? Does ...
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428 views

The relation between classical from quantum vs measurement problem

What is the relation between classical from quantum vs measurement problem. On the one hand they seem to be related on the other they seem to be of different nature. We always see our screens in ...
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2answers
537 views

Transition from one state to another in Quantum Mechanics

When we measure an electron's position we know that the wave function $\psi$ peaks at the measured position and the wave function as a function of momentum is a harmonic function. When it makes the ...
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2answers
258 views

Doesn't Schrodinger's Cat depend on whether there's a quantum/classical boundary?

Everyone knows how Schrodinger's Cat is set up, so the question becomes whether there's a quantum/classical boundary and what that boundary is. Some people say everything is quantum while some may ...
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Compatible Observables and Measurement

Suppose $A$ and $B$ are compatible observables (i.e. $[A,B] = 0$). We take the eigenkets of $A$ to be $|a_1 \rangle \ldots |a_N \rangle$. Further, we suppose that the first $k$ eignekets of $A$ are ...
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Why superpositions? [closed]

I've seen a lot of stuff on superpositions, namely the double slit experiment. And every video I watch, it tells me the same thing: It's amazing that when these particles are being observed they ...
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What the wave function looks of a particle in the infinite square well looks like after collapse for measurements of position and energy

Consider a particle in a the infinite square well from x=0 to x=L. At t=to, I make a measurement of position and get x=L/2. What is the resulting wave function at t=to? My understanding, from reading, ...
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Is a photon always in a state of superposition while traveling through space?

In the double-slit experiment, we emit a photon that is in a state of superposition (wave form) which travels through both slits to interfere with itself. When we measure which slit it went through, ...
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Has this experiment really demonstrated wave-function collapse?

My question is: why did the following experiment claim that it had demonstrated the wave-function collapse? Experimental proof of nonlocal wavefunction collapse for a single particle using homodyne ...
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The nature of measurement

Does the measurement of the particle change it's physical state? Or does it only seem to do that? Ex. if a particle was measured before the slits, would we see an interference pattern, or a particle ...
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2answers
731 views

Double slit experiment paradox

Two observers – A & B - conduct a single double slit experiment and watch the same detector screen for the appearance of an interference pattern. A separate detector records which slit each ...
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Time reversal on superposition: I think [duplicate]

Imagine I have a box, and in it, I have a photon in a superposition of state |1> and |0>. I look into the box and register that the photon is in state |1>. Now, if I have ALL information in the ...
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Eigenstate vs collapsed wave function

An eigenstate, or determinate state, is a state where the measurement of some observable always yields the same result. This means that the standard deviation of the observable is zero. If a ...
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How do probabilities emerge in the many-worlds interpretation?

My understanding is that at each quantized unit of time that a split occurs, every possible recombination of particles occurs in the 'objective' universe. If this is the case, what relevance to ...