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 “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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How does gravity-spacetime interaction modulate the Casimir force? [closed]
Suppose there is a point source of strong gravity. Far away from this point source in terms of the speed of light, there exists a vacuum in space where no dust is. This vacuum nonetheless can ...
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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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What is algebraic structure, operation or relation explains relationship between the 2 diagonal terms of the 2 density matrices?
Quantum decoherence therefore prescinds from the observer and from the measurement process in a certain way preceding it and simulating the collapse of the wave function.
In particular, "...
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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 and measurement in simple terms?
I don't know about physics. Say there are only two electrons in the universe, so there is a probability distribution of their position, speed etc. They are in each other's observable universe so they ...
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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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Can decoherence account for suppression of interference in all basis?
Let the system formed by particle(microscopic or macroscopic)- environment coupling be described by $|\phi><\phi| $ . In decoherence approach, to retrieve the classical properties, one focuses ...
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Does this thought experiment proves that Standard Quantum Mechanics and Pilot Wave Theory make different predictions?
Here is a thought experiment that is supposed to show that standard quantum mechanics and pilot wave theory do not make the same prediction :
Take the double slit experiment, and add a detector in ...
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Signal coherence/correlation vs quantum coherence
In general, I understand a signal $s(t) \in \mathbb{C}$ is called "coherent" when it has a large autocorrelation function. A pair of different signals $s(t)$, $r(t)$ can also be "coherent" if their ...
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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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Mathematical aspects of decoherence
I am trying to understand the maths behind decoherence. I first state the framework I am working with, and then I ask my questions.
Let $H_A$, $H_B$ be finite dimensional Hilbert spaces ("the system" ...
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How do we know which states are decohered by the environment?
If I take an atom in a momentum eigenstate, or just a very narrow gaussian in momentum space (with a very large spread in position space), and then I throw it into a gas, it will quickly decohere into ...
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Why does the interaction with environment remove the basis ambiguity : decoherence theory
In decoherence theory, we try to remove the measurement postulate from Q.M to replace it by unitary evolutions.
Consider a two level system $S$, an apparatus $A$ and the environment $E$.
A first ...
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What was exactly the preferred basis problem in decoherence?
I am reading some papers of Zurek, for example this one :
Pointer basis of quantum apparatus: Into what mixture does the wave packet collapse?
He starts to introduce a way to define a measurement ...
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How often do particles regain quantum coherence after decoherence?
Quantum decoherence is "well known" process. It is simply defined as a loss of quantum coherence. It is often used as a partial explanation for "collapse of the wave funtion" (wave funtion is ...
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Quantum Coherence in a Two-level System in the Density Matrix Formalism
Dealing with semiclassical light-matter interaction, in particular the interaction between an electromagnetic field and a two level system using the density matrix formalism, I learned that the system ...
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Is this decoherence?
I have a very basic understanting of decoherence (i.e. I,ve read the Wikipedia page), but I was recently reading Heisenberg's The Physical Principles of the Quantum Theory and I came across a thought ...
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How does thermalisation make incoherent waves into coherent ones?
Thermalisation is the process by which out-of-equilibrium systems reach equilibrium. Coherence refers to the phases of waves being a constant difference apart.
While reading a paper on axion stars, I ...
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What is meant by collapse of wave function? [closed]
Collapse of wave function ,does it really happens?why?
