Questions tagged [measurement-problem]
DO NOT USE THIS TAG just because your question involves measurements (either quantum or classical). The measurement problem asks how wave function collapse occurs during measurement in quantum mechanics, and how it can be reconciled with unitary evolution.
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Weak measurements, non-demolition measurements and interaction-free measurements vs. wave function collapse [closed]
Let $\psi \in \mathcal{H}$ be a (pure) state of some physical system and suppose we measure an observable $A$ (represented as self adjoint (say bounded) operator, i.e. an element of $\mathcal{B}(\...
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How do I calculate the probability distribution of momentum assuming that my instrument has a small spatial extension?
Let us consider a particle in a one-dimensional space (X-axis) whose state, at a given instant of time, is described by a given wave function.
Let us assume that we measure the momentum p using a ...
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On the wave function collapse
I'm particularly concerned with the conceptual consequences of this postulate, which I never quite pondered enough.
In quantum mechanics, wave function collapse, also called reduction of the state ...
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Has quantum measurement and particle appearance ever been modelled as a resonance effect created by the measuring device on the quantum wave?
Has anyone ever modelled quantum measurement as a resonance effect, that is created by introducing a measuring device into the quantum system?
An analogy may explain what I mean: if you take the free ...
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How does wave function collapse relate to uncertainty in position when measurement intervals approach zero? [closed]
In quantum mechanics, measuring the position of a particle causes the wave function to collapse, fixing the particle at a measured position. Given this collapse, how can it be claimed that as the ...
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Can the measurement problem be overcome? [closed]
I was listening to some physicists discuss the issues with measurement in quantum mechanics and some of the earlier philosophical repercussions. However in most cases where measurement affects a ...
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Is there a resolution to the "Wigner's Friend" paradox?
Suppose that two observers $A$ and $B$ are mutually isolated, observer $A$ measures the state $|0\rangle + |1\rangle$ and concludes that the result is $|0\rangle$.
However, observer $B$ concludes that ...
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What happens if two people have different knowledge about a state in a quantum mechanical system?
Let’s say I measure the spin of an electron, but I don’t tell you what it is and you don’t measure it yourself. Does that change the wave function for you or does it remain the same either way? If it ...
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Does a Quantum System Really "Jump" to an Eigenstate When Observed?
Warning: This is a highly hypothetical question.
I am bothered with Dirac's description of the system when making a measurement. Without quoting his statement (from The Principles of Quantum Mechanics,...
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On the Measurement Problem
In the orthodox interpretation of quantum mechanics, the following three assumptions are made (please correct me if I am wrong):
Every physical system is completely specified by a state $\lvert\psi\...
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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 ...
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Position operator action on a wavefunction [closed]
In a 1 dimensional infinite potential well with width $a$, the ground state wave-function is given by
$$\psi(x) = \sqrt{\frac{2}{a}}\sin(\frac{\pi}{a}x)$$
The action of the position operator in the ...
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Exact time evolution of Stern-Gerlach (SG) apparatus
Background: I was always under the impression that when considering the Stern-Gerlach (SG) Experiment, the interpretation of the split of the beams is that the spin $1/2$ particle get measured the ...
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Doubts on my interpretation of Wigner’s friend scenario
I have some doubts regarding my personal interpretation that i was contemplating about in the context of Wigner's friend experiment (also tested in the laboratory).Could it be that a system is always ...
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Understanding Wigner’s friend scenario
I recently watched this video https://youtu.be/Wsjgtp9XZxo?si=sIRlAbvAm2wjXRNP
and tried (unsuccessfully, because i don’t have the knowledge required) to read Bruckner’s paper.
What i am missing, is ...
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Ontologically speaking, does single-shot quantum interference occur in pairs of possibilities?
I've been perplexed by the semantics used in Science 329, 418-421(2010), where they state that according to
Born’s rule and its square exponent, interference always occurs in pairs of possibilities.
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Andromeda paradox and quantum mechanics
Roger Penrose introduced the Andromeda Paradox as a thought experiment that delves into the implications of relativity and quantum mechanics on our understanding of simultaneity and reality. The ...
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Fundamental randomness unprovable? [closed]
Is it too strong a claim (i.e. unprovable) to say that no being (hypothetical or otherwise) could possibly predict the outcome of every individual measurement of any quantum system with certainty? ...
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How can the Copenhagen and Everett interpretations of quantum mechanics make the same predictions?
Suppose we have a spin $\frac{1}{2}$ particle in the spin-up state along the $z$-axis, $\lvert \uparrow \rangle$, and after $t$ seconds of evolution under the Schrodinger equation it is in state $\...
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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 ...
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What exactly is a "measurement" in quantum mechanics?
*I can't see immediately whether or not this post constitutes as a duplicate, but I wouldn't be surprised if it does. If that is the case, then please reference me the post that I'm duplicating so ...
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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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Measurement problem and precise mathematical calculation
The infamous measurement problem is a problem in the foundations of quantum mechanics: different people have different views how to understand this problem: some people even deny that there is any ...
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Are there any other nondeterministic processes than measurement in quantum theory?
Nondeterministic refers to a system or process that does not have a single predictable outcome. In other words, when a system is nondeterministic, it means that multiple outcomes are possible for a ...
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How to obtain quantum-state purity and concurrence by measurement on quantum computer?
My whole question is aimed at the implementation on quantum computers utilizing quantum circuits, i.e. we can assume, that I can prepare several "copies" of the same state, without really ...
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Quantum Measurement and the law of thermodynamics
When discussing the conceptual issues of quantum mechanics, concepts like Bell's inequality, non-locality, and the Kochen-Specker theorem are often brought up. Many physicists have dedicated time to ...
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Why is this a correct explanation for the Uncertainty Principle? [duplicate]
There's this really common explanation for Heisenberg's Uncertainty Principle, but I quote it from Classical Dynamics by Marion and Thornton:
The wave character of the photon precludes an exact ...
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Is projective measurement a channel that results from a unitary evolution on both the system and the apparatus?
I was researching the motivation behind introducing quantum channels and this is essentially what I've gathered.
Suppose we have two subsystems, the system we're interested in where states exist in ...
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Will the electron interference remain if the photon scattering method doesn't include a photo-detector? Is it an example of quantum entanglement?
It is actually not a question. I am giving a chain of arguments here , I believe at some point I made a mistake. I want the mistake to be pointed out.
/1. The probability of an event in an ideal ...
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Nielsen and Chuang general measurements and POVM
I'm reading Nielsen and Chuang's famous book on Quantum Computation and Information. In section 2.2 on the postulates of quantum mechanics, they talk about quantum measurements starting with
Postulate ...
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What is the 'charge' and 'mass' of an electron means before measurement?
What I have learnt: We can't talk about an electron's position,momentum,angular momentum,energy...anything 'before the measurement'. An electron simply doesn't have these physical parameters before ...
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Ideal quantum measurement
Schlosshauer (in Decoherence and the Quantum-to-Classical Transition) defines ideal quantum measurement as a von-Neumann measurement in which
(1) the apparatus states correspond 1-to-1 to given system ...
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On the field leakage problem in quantum experiments
In a quantum experiment, does the leakage of the electromagnetic fields lead to the suppression of quantum effects? For example if I have an electron in a box, in some quantum superposition. Can I use ...
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Measurement Problem Explained by Interaction of Operator With Adjoint Having Larger Domain?
Quantum physics axiomatically uses a self-adjoint operator for a measurement. In general, the adjoint of an operator has a larger domain than an operator. Could it be that the "measurement ...
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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 ...
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Is the many-worlds interpretation less ill-defined than the Copenhagen interpretation? [closed]
In my understanding, the Copenhagen interpretation is ill-defined in the following way. The interpretation says that wavefunctions collapse when a measurement is performed. But the Copenhagen ...
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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 ...
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How to describe collective spin measurement in QM?
What is the QM description for measuring the collective magnetisation of an abitrary number $N$ of protons?
For example, say that the density matrix is separable (no initial entanglement between ...
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Is a PBS a measuring device without observer?
Let a photon In superposition of v and h polarization is going through a Polarizing beam splitter PBS. If it passes, it is in h polarization on path A, otherwise is in v on path B. Let have a detector ...
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Testability of consciousness-causes-collapse interpretation
The consciousness causes collapse a.k.a. Von Neumann–Wigner interpretation says that the wavefunction collapse occur only at the point when a conscious being observes the result. I myself find it ...
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Average value of 3 measurements [closed]
Some physical quantity was measured two times. It’s average value is equal to 5. The reading of the third measurement is equal to 2. What is the average value based on the results of three ...
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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 ...
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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 ...
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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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What is an agent in the Quantum Bayesianism/Relational Quantum mechanics-like interpretations?
In interpretations like Quantum Basyesianism, Relational interpretation, Information Theory interpretation, etc, the wavefunction represents the probabilistic knowledge that an agent holds about a ...
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Nature of expectation values and Born's rule and the measurement problem
Suppose we take a normalised quantum mechanical wave function of $\Psi (\mathbf{r} ,t)$.
If we expand it in a certain form of spatial functions $\psi_{n} (r)$ which is complete orthonormal. Then we ...
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Does the inside of a solid object not interact with the outside environment? But how does quantum decoherence happen?
We have learned that quantum decoherence is caused by interaction with the environment. However, inside our body, there is no interaction with photons or air molecules in the environment, so how does ...
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How can the Copenhagen interpretation possibly be redeemed of this contradiction? [closed]
It seems like the Copenhagen interpretation is just self contradictory. These two axioms are contradictory:
Quantum Mechanics describes all the particles in the universe
Measurement devices evolve ...
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Is the Born rule a red herring in explaining the measurement problem? [closed]
Many explanations of the measurement problem try to derive the Born rule from Schrodinger evolution, for example Many worlds. I have two reasons to think the Born rule isn't fundamentally related to ...