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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Reduced density matrix time evolution

So, I'm trying to study the interaction between a harmonic oscillator-like particle (with variables $X$ and $P$) and a heat bath, also modeled by a compound of $N$ harmonic oscillators, with variables ...
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How do you compute saddle point approximation of path integral for open quantum system?

Note: the question in this post is basically originated from here. Please refer to it first if you don't get the sense. I'd like to know how you compute the saddle point approximation in the path ...
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Is $ \hbar \rightarrow 0 $ in path integral merely technical thing? Is there any justification? (especially in open quantum theory)

I wonder whether the limit $ \hbar \rightarrow 0 $ in path integral is merely technical stuff when we explain the classical limit of quantum mechanics, or there may be any physical meaning or sense ...
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Understanding decoherence in the double slit experiment [duplicate]

I am trying to understand how decoherence explains the observation of only one possible outcome rather than observing the superposition. When the electron goes through the two slits it interferes with ...
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the measurement problem, what is it that drives the wave function to collapse?

I'm hearing a lot of different solutions to the measurement problem. But what is the right answer? Does consciousness play a role in the collapse of the wave function or is there a different factor at ...
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What does this quantum mechanics diagram about adaptive mutations mean? [closed]

I'm a current high school student and I’m aspiring to become a biochemist. I’m at the moment writing an article about adaptive mutations but there is a lot of tricky quantum mechanics in it which I ...
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Why is decoherence considered to be a 'trick' used for practical purposes?

As I understand, decoherence consists of making the observation that when we trace out the environment from the overall density matrix of the system, we get von Neumann's projection postulate state ...
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Is the Copenhagen interpretation still the most widely accepted position?

In my undergraduate Quantum Mechanics textbook (Griffiths), of the Copenhagen interpretation it says "Among physicists it has always been the most widely accepted position". I'm currently ...
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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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Regarding the quantum nature of floating gate transistor - tunneling, coherence, spectrum

In a floating gate transistor, the gate is electrically isolated. I have a few questions regarding the quantum nature of this device: It is sometimes mentioned that, to store or deduct charges from ...
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What causes quantum entanglement to end?

I seems strange to me that I could not easily find information on "when quantum entanglement ends?", "What causes quantum entanglement to end?". Google search finds explanations of ...
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What is 'coherence' of a quantum system (with examples)?

The term 'coherence' is frequently used in relation to certain quantum systems such as LASER, superconductors, etc. Please help me understand what we mean by the coherence of a quantum system. How do ...
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The structure of Worlds in Many Worlds theory

I've read David Deutsch's article where he explains - in terms of information flows - how different Worlds can be located in the same 3D space (as we perceive it) while do not interact with each other....
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Can someone explain the measurement problem with little bit of mathematics?

Can someone mathematize the statement of the quantum measurement problem? I am only interested in the statement of the problem (and not its solutions). Thanks. Still confused. Stated in this way (as ...
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What are fundamental reasons for conservation laws in Quantum Mechanics?

Let me be a little silly and suppose that when "God" created our Universe - he had these 3 options: (Most classical): let the energy (contained in any particle = field excitation) spread ...
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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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Quantum decoherence reversibility

Let us say we have a particle in a superposition of spin-up and spin-down at time $t_1$. The particle is measured as spin-up at time $t_2$ by an observer. At the current time, $t_3$ all traces of ...
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Can an atom first obey Schrodinger equation and after obey the heat equation?

This question is related to this other question. I first consider an atom in a cat's superposition. It obeys the Schrödinger equation. The idea would be to make it weakly interfere with a thermal bath ...
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Is the universal wavefunction globally coherent?

In Wikipedia's article on quantum decoherence, it states that despite decoherence creating the appearance of wavefunction collapse, A total superposition of the global or universal wavefunction still ...
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Schrödinger's Cat: Are the different quantum states inside the box coherent before it's opened?

Assume that the walls of the box prevent any interaction between the inside and the outside. Are the different quantum states within the box (living cat, dead cat, and all permutations thereof) ...
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What is the connection between decoherence and phase relationships?

Every answer explaining decoherence brings up the concept of phase relationships, but I'm just not seeing the connection. In the double slit experiment, for example, it makes some intuitive sense to ...
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Talbot-Lau effect to investigate decoherence of fullerene

I am reading Decoherence and the Quantum-To-Classical Transition, which describes the experiment of investigating the dynamic of decoherence by making interference of fullerene molecules. Such ...
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Non-observance and the Schrödinger equation

I was thinking today about configurations where one measures that a certain observable is not in a certain state. I was getting confused about what this means for decoherence. If I observe a detector ...
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Predictability in decoherence theory to find the classical states: at which time must we evaluate?

I have read Decoherence, einselection, and the quantum origins of the classical, end a way to quantify the classicality of states is the following. We have the system $S$ and its environment $E$. The ...
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Is the Schrodinger's Cat experiment possible in principle?

There are already lots of questions (and great answers) regarding Schrodinger's Cat (and Wigner's Friend, which is the same concept) on here. For example, this post is a great explanation of how ...
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Decoherence: Does the environment must be a tensor product of two sub-systems to remove any ambiguity?

In decoherence theory, we describe the decoherence of a system $S$ by the mean of an interaction with an environment. In short, if I consider: $|\psi_S \rangle=a|0_S\rangle+b|1_S\rangle$, the system ...
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Does the spin measurement of entanglement need to be simultaneous?

We know that after measuring the spin direction of two entangle particles the entanglement breaks down due to decoherence and this measurement can only be done once. So if that's the case then it ...
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Quantum measurement limit of decoherence and scattering: why are position pointer said classical?

In decoherence theory, we explain the decoherence by hamiltonian evolutions between a system and its environment. Calling $H$ the total hamiltonian, I have: $$H=H_S + H_E + H_{SE} $$ A pointer state $|...
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Measurement outcomes of a “not totally decohered” system

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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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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Decoherence and einselection model: Contradiction with two different explanations?

I am a little puzzled by einselection models. I followed those two papers (Environment-induced superselection rules Decoherence, einselection, and the quantum origins of the classical) to understand ...
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Bounds on the locality of single-particle coherence

It's well known in the multi-partite setting that entanglement can't be generated by local operations and classical communication; indeed, this is often taken as one of the defining properties of ...
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Fermionic operators, bipartite systems and partial traces

Consider a composite system (e.g. a system $S$ and a bath $B$) and fermionic operators $s_i$ and $b_j$, where $s_i$ annihilate fermions in $S$ and $b_j$ annihilate fermions in $B$. Obviously, \begin{...
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How do crystals protect electronic spin qubits?

Defects in SiC crystals demonstrated entanglement between electronic spin qubits at room temperature. But do we need a crystal to protect the state? My understanding is that crystals, being uniform ...
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Decoherence and quantum to classical limit: good resources?

I am looking for good references for decoherence theory. I mainly worked with "Decoherence, einselection, and the quantum origins of the classical" from Zurek, but some parts are a little bit ...
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How does einselection fit into quantum decoherence?

My understanding of decoherence is the following: There is a system state vector $|\Psi\rangle_s$ and the environment state vector $|\Psi\rangle_\epsilon$ which are combined to form $|\Psi\rangle_s \...
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When does a collision become classical?

I was thinking (after misinterpreting and answering another question) about collisions on the atomic scale. I know it's impossible to visualize, but I did. For example the collision between an ...
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Quantum decoherence revisited

I asked a question about whether decoherence is dependent and received some helpful replies (thanks!). I tried to leave a comment detailing the article I was reading, but it was too long to be ...
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Is quantum decoherence basis-dependent?

Is quantum decoherence basis-dependent? I've seen claims for both 'yes' and 'no'. Could someone provide a nice simply explained example (geared to an amateur quantum mechanic) that demonstrates the ...
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Can decoherence provide a loophole for FTL communication in a system of multiple entangled particles?

I am a layperson when it comes to the study of quantum mechanics and do not quite have the expertise to properly evaluate the questions I am going to post here. But here it goes. Suppose three ...
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Can we tell if a particle has collapsed due to a measurement?

Suppose we have two electrons A and B. My friend measure the spin on electron B the value is +1/2, and he writes on a piece of a paper the value. Electron A has not been measured, so the spin is in ...
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Decoherence Tutorial on level of the Theoretical Minimum books

I'm trying to understand decoherence and other issues in QM related to the Everettian interpretation. I have a BS in physics, but that was 37 years ago. I've read Susskind and Friedman's book, The ...
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Can a macroscopic object decohere by itself (even when it would be somehow completely isolated) or does it need an environment?

Is there such a thing as self decoherence? What I Mean is, I’ve read that because macroscopic objects (like billiard bals) interact with their environment they decohere and can’t be found in a ...
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Do quantum effects of macroscopic objects dissapear because of decoherence or because large objects have small wavelenghts, or both?

I’ve read that the wavelength of macroscopic objects is so small that it’s effects are negligible so the object can be described with classical physics, and that decoherence causes quantum effects to ...
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Density operator diagonal terms during decoherence

On page 7 of this paper by Sebens and Carroll they discuss the diagonal terms of the reduced density matrix during decoherence. I am very confused. I thought the diagonal terms are the only ones that ...
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Why can’t macroscopic objects like apples be isolated but a photon can?

I read that the reason that macroscopic superpositions decohere is because it’s difficult/impossible to isolate macroscopic objects from the environment. Why is this so difficult/impossible and why ...
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Probing the relation between decoherence theory versus the arguments based on the smallness of $h$ in connection with the quantum classical transition

This question tries to relate the elementary account of quantum effects in the macroscopic domain in terms of the smallness of the quantum of action, which is usually presented in introductory quantum ...
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Are superpositions contagious?

Does quantum mechanics really predict that a particle prepared in a state of superposition of spin will result, after being measured by an appropriate instrument (Stern-Gerlach device), in a ...
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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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