Questions tagged [decoherence]

Quantum decoherence is the irreversible loss of ordering of the phase angles between the components of a system in a quantum superposition resulting in classical or probabilistically additive behavior, thereby suppressing interference of wavefunction components.

Quantum decoherence is the irreversible loss of ordering of the phase angles between the components of a system in a quantum superposition, resulting in classical or probabilistically additive behavior, thereby suppressing interference of wavefunction components. Decoherence can be viewed as loss of information from a system into the environment, to simulate/explain ''apparent wave function collapse", the quantum features of the system leaking into the environment. That is, components of the wavefunction are decoupled from a coherent system, and acquire phases from their immediate surroundings.

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Why doesn't a typical beam splitter cause a photon to decohere?

In many experiments in quantum mechanics, a single photon is sent to a mirror which it passes through or bounces off with 50% probability, then the same for some more similar mirrors, and at the end we get interference between the various paths.…
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What is the quantum mechanical definition of a measurement?

I hear the word "measurement" thrown around a lot in quantum mechanics, and I have yet to hear a scientific definition that makes sense. How do we define it?
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Why can interaction with a macroscopic apparatus, such as a Stern-Gerlach machine, sometimes not cause a measurement?

Consider a Stern-Gerlach machine that measures the $z$-component of the spin of an electron. Suppose our electron's initial state is an equal superposition of $$|\text{spin up}, \text{going right} \rangle, \quad |\text{spin down}, \text{going right}…
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Would every particle in the universe not have some form of measurement occurring at any given time?

I know this is probably a common point of confusion, but I have a specific question about measurements in Quantum Mechanics. I read an explanation on this, but still have a point of confusion. The explanation of why a measurement somehow affects…
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Is the preferred basis problem solved?

Once and for all: Is the preferred basis problem in the Everettian Interpretation of QM considered solved by decoherence or not? THere are a few people who claim that it's not, but it seems the vast majority of the literature says it has been solved…
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What are the strongest objections to be made against decoherence as an explanation of "collapse?"

When we measure an observable A of a quantum system, we get an eigenvalue of A. Without worrying about connotations of Copenhagen vs. MWI, etc., let's just call this "collapse." Question: Among people who are not convinced that decoherence gives a…
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Is the collapse of the wave function inherently time asymmetric?

Schroedinger's equation, as we all know, is time symmetric. In quantum field theory, we have to come up with a more sophisticated CPT reversal, but the essential point remains unchanged. However, the collapse of the wave function in the Copenhagen…
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Reversing gravitational decoherence

[Update: Thanks, everyone, for the wonderful replies! I learned something extremely interesting and relevant (namely, the basic way decoherence works in QFT), even though it wasn't what I thought I wanted to know when I asked the question. Partly…
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Decoherence. Does it solve the measurement problem? Is it discontinuous? When does it occur?

I am trying to better understand the current scientific consensus (to the extent that such a thing exists) on the interpretation of quantum physics. I understand that this is still very much an active area of research but it seems to me that there…
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Are Thomas Breuer's subjective decoherence and Scott Aaronson's freebits with Knightian freedom the same things in essence?

In his remarkable works (1,2 and their recent development 3) Thomas Breuer proves by diagonalization the phenomenon that the observer cannot distinguish all phase space states of a system where he is contained, a theorem paralleling the famous…
Anixx
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How is it possible that quantum phenomenons (e.g. superposition) are possible when all quantum particles are being constantly observed?

I don't understand how quantum mechanics (and therefore also quantum computers) can work given that while we work with quantum states, particles that this quantum state consist of cannot be observed, which is the most fundamental requirement. If I…
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A tutorial explanation of decoherence?

Is there a tutorial explanation as to how decoherence transforms a wavefunction (with a superposition of possible observable values) into a set of well-defined specific "classical" observable values without the concept of the wavefunction undergoing…
Nigel Seel
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Is the wavefunction of particles inside a gas spread or localized?

For an individual free particle that starts localized, the wave function packet spreads over time, so the particle becomes less localized. Suppose now that we have a gas of those particles inside a box, and we allow them to collide (using some…
user83548
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Is decoherence even possible in anti de Sitter space?

Is decoherence even possible in anti de Sitter space? The spatial conformal boundary acts as a repulsive wall, thus turning anti de Sitter space into an eternally closed quantum system. Superpositions remain superpositions and can never decohere. A…
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Why do particles tend to collapse to *energy*-eigenstates (rather than some other basis)?

My understanding from reading about quantum mechanics is that the state of a particle such as an electron can be kept in a superposition of energy states for an extended period of time, when it is not interacting with other particles, but that as…
user56834
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