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.
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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 ...
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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} \...
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Would every particle in the universe not have some form of measurement occurring at any given time? [duplicate]
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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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, ...
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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 ...
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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 ...
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What is the difference between classical correlation and quantum correlation? [duplicate]
What is the difference between classical correlation and quantum correlation?
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Born's rule and Schrödinger's equation
In non-relativistic quantum mechanics, the equation of evolution of the quantum state is given by Schrödinger's equation and measurement of a state of particle is itself a physical process. Thus, ...
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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 ...
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Why does the electron wavefunction not collapse within atoms at room temperature in gas, liquids or solids due to decoherence?
Decoherence theory predicts that any quantum particle coupled to any "large" environment should undergo decoherence and its wavefunction should collapse. This explains why measurement leads to ...
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Are quantum decoherence and Everettian approaches to the measurement problem necessarily distinct?
As I understand it, there is a large contingent of physicists who believe that the measurement problem is "solved" by decoherence, without, for example, needing to postulate the existence of "many ...
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Decoherence and Young's double slit experiment
If we shine light on an electron wave passing through a double slit then the interference pattern is destroyed. This is now understood as decoherence coming from interaction of the electrons with ...
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Did Leggett and Caldeira solve the measurement problem?
In 1983 Leggett and Caldeira published a paper (see also here) that shows the evolution of the density matrix in a dissipative system. Follow-up work by Zurek and others shows the relevance to ...
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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 ...
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Do measurements of time-scales for decoherence disprove some versions of Copenhagen or MWI?
Do measurements of time-scales for decoherence disprove some versions of Copenhagen or MWI?
Since these discussions of interpretations of quantum mechanics often shed more heat than light, I want to ...
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Is the Copenhagen interpretation merely an approximation to quantum mechanics?
So, I'm reading Max Tegmark's Our Mathematical Universe (Knopf edition, p. 229). He's discussing Everett/MWI for a bit and I'm not really paying attention and then I wake up to this:
[I]t's time to ...
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Why doesn't gravity mess up the double slit experiment?
So let's say you are doing a double slit experiment. Also, let's use electrons.
My question is, won't the gravity of the electron affect the earth, thereby causing it decoherence and its wave ...
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Can a super-positioned human be used to differentiate between the Copenhagen interpretation and many-worlds?
I'm pretty new to quantum physics, so there's a good chance that I have this all backwards.
However, by my understanding of the Copenhagen interpretation, the wave function 'collapses' upon ...
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Schrödinger's cat and the difficulty of macroscopic superposition state
The Schrödinger's cat was regarded as peculiar since we seldom encounter a superposition state in macroscopic scale: $$ \mid \mathrm{dead \,\,cat} \rangle + \mid \mathrm{alive \,\, cat}\rangle $$
We ...
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Can the Montevideo interpretation of quantum mechanics do what it claims?
Partly inspired by the great responses to a my previous physics.SE question about "reversing gravitational decoherence, today I was rereading the intriguing papers by Gambini, Pullin, Porto, et al., ...
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Can observers be particles?
Generally Quantum mechanics divides a system what is to be observed and an observer. This is generally taken to be some human being. But why restrict it to such? Why not a particle?
Is there a good ...
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Is the wave function of a particle re-created after a measurement stops?
Yeah, I haven't quite understood, or been told, what happens to, for example an electron and its wavefunction, when you stop to measure it.
I mean, an electron has a wave function describing its ...
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What does spontaneous symmetry breaking have to do with decoherence?
Background
The question here by Prof. Wen, and the answers that follow point out that spontaneous symmetry breaking (SSB) has something to do with decoherence if I understand it crudely correctly.
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Does sluggish decoherence in deep space have any noticeable effects?
It is well established that quantum mechanical systems lose their coherence over time due to interaction with an uncontrollable environment. In particular, Professor Haroche, among others, has ...
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What is the quantum structure of the interstellar matter?
Consider an interstellar medium of one hydrogen atom/cm$^3$ with $500$ photons/cm$^3$ coming from CMB. This density of particles is very weak according to quantum decoherence. So, according to ...
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Any link between decoherence and renormalization?
I have been studying decoherence in quantum mechanics (not in qft, and don't know how it is described there) and renormalization in QFT and statistical field theory, I found at first a similarity ...
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Has the Copenhagen Interpretation remained accurate?
Almost a century past, has the Copenhagen Interpretation (CI) undergone any modification? In other words, has any of its underlying principles been reformulated since?
The notable (usual) examples ...
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How does a Wavefunction collapse?
How does a wavefunction collapse into one state? More specifically, what conditions cause a wavefunction for a quantum particle to collapse?
Does this have to do with density matrices?
Please ...
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Decoherence and collapse
It is said that the decoherence does not solve the problem of measurement and/or the emergence of classicality, can somebody explain it with simple analogies or in a manner accessible to a non-...
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Does uniqueness of the triorthogonal decomposition make quantum measurement objective?
Some books and articles on quantum measurement theory make use of a theorem (by Elby-Bub 1994) called the Triorthogonal Decomposition Theorem:
For three subsystems, a state vector $\lvert \Psi \...
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What is behind recoherence?
I am quite familiar with the concept of decoherence, and I heard that a system that has decohered could recohere after that, I was wondering what could cause the the coherences that have leaked into ...
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Conservation of quantum coherence?
Is coherence conserved under unitary transformation?
As we saw in the process of generating entanglement, coherence between states of the subsystem is transferred to quantum correlations (related to ...
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Reason for decoherence time's dependence on variables?
Zurek 2001 is a review article on decoherence in quantum mechanics. Equation 5.36 on p. 24 gives an estimate of the decoherence time, which I'll paraphrase as follows:
$ \frac{t_D}{t_R} = \left(\frac{...
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Why doesn't decoherence spoil the double slit experiment? [duplicate]
Imagine firing one electron at a time at a double slit. Clearly the wave function interacts with the atoms of the material, and presumably many electrons do not pass through. Why does decoherence from ...
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Coherences in the density matrix
It is said that the off-diagonal elements of density matrix are "coherence". When a system interacts with its environment the off-diagonal elements decay and the final density matrix is the diagonal ...
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Kraus operators for two interacting harmonic oscillators: Problem with the calculation (Ex. 8.21 of Nielsen-Chuang)
I'm working with Exercise 8.21 of the Nielsen-Chuang book on quantum information. It illustrates the amplitude-damping quantum channel by the interaction between two harmonic oscillators (the first ...
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Pure dephasing $\gamma_\phi$ in a master equation and noise power spectral densities
In its simplest form, my question is regarding a two level system of transition frequency $\omega_0$ given by the Hamiltonian
\begin{equation}
H = \frac{\hbar \omega_0}{2}\sigma_z
\end{equation}
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Meaning of "realism" in quantum mechanics
When physicists doing work in quantum measurement, decoherence, Bells' inequalities etc. use the term "realism" what exactly do they mean?
I'm looking for answers targeted towards, say, someone whose ...
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What makes quantum decoherence different from dissipation?
From my understanding quantum decoherence and dissipation are completely different ways of modelling information loss to the environment. Dissipation can be modeled using the Caldeira-Leggett model ...
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What is the preferred basis objection to the many-worlds interpretation of quantum mechanics?
I've seen the preferred basis problem referred to in many places, but have not seen a clear explanation of what the problem is. For example, this question asks whether the problem has been solved, but ...
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Fermi's Golden rule: Accounting for Decoherence
On the Wikipedia page for Fermi's golden rule, there is a vague statement that is given in passing:
... if there is some decoherence in the process, like relaxation or collision of the atoms, or like ...
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If all the particles of a Bose-Einstein condensate become entangled with each other,does the system still remain a Bose-Einstein condensate?
I know that an entangled system is found in a single entangled state and that when you try to observe the individual state of a particle from an entangled system using a reduced density matrix, you ...
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How does quantum decoherence occur?
My question is how does quantum decoherence happen. What happens with a quantum system when "observed?" Can you give a mathematical explanation that is simple, precise, and easy to understand?