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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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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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Correlation functions of quantum Ising models

I have a single technical question regarding a statement on page 7 of the paper "Dynamical quantum correlations of Ising models on an arbitrary lattice and their resilience to decoherence". The paper ...
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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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Measurement collapsing wave functions [duplicate]

I'm sure variations on this come up a lot, but I was specifically interested in a response to a claim made by a particular article: https://medium.com/@roblea_63049/the-double-slit-experiment-...
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Optical coherence versus quantum coherence

Optical coherence is usually defined to be the measure of statistical correlation (for example if the phase difference is constant) of a pair of waves. Recently I came across the notion of quantum ...
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1answer
131 views

Do all well-measured observables effectively commute?

Do all well-measured observables effectively commute with each other? The rest of this long post clarifies what I mean by that simple-looking question. Consider quantum field theory in Minkowski ...
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Can the many worlds interpretation use the Born rule for decoherence? [closed]

If the Many-Worlds Interpretation cannot derive the Born rule does it need mind body dualism to make sense of probabilities? I asked a different question here regarding MWI and circularity. But here'...
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Decoherence: faster than light?

The answer to this question suggest that one can solve the measurement problem by decoherence. If I understand it correctly the decoherence appears when the quantum state interacts with the ...
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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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Why do we need the third axiom of QM to explain the wave function collapse? Why don't we use the decoherence process as an axiom?

I've always seen the standard interpretation and axioms of QM as in some way tricky on a philosophical level. They state the collapse of the wave function is caused by the measurement. 3.b If $A$ ...
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Difference between decoherence and wave function collapse

What's the difference between The phenomenon of decoherence and the quantum wave function collapse ?
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Derivation of the master equation without using the Markov approximation

In this paper, pg 27, the master equation for reduced density matrix is derived using only two assumptions: 1) the initial total density matrix is unentangled, i.e. tensor product of system and ...
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Confusion about why deducing pointer observable from the structure of the Hamiltonians is not practical

I am trying to learn Zurek's theory of decoherence. Right now I am reading Decoherence, einselection and the existential interpretation (the rough guide) which seems like an easier read than his big ...
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Never ending quantum superposition? [closed]

So I am wondering over the Copenhagen Interpretation how can a decoherence or measurement ever happen. If in the beginning of the universe everything was in a state of coherence being in ...
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Equivalence of quantum state diffusion and heterodyne trajectory

According to Breuer-Petruccione, the SDE quantum trajectory evolution for heterodyne detection $$d\psi=-iH\psi dt-\frac{\gamma}{2}\left(C^\dagger C-\langle C^\dagger \rangle_{\psi} C+\frac{1}{2}\...
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1answer
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Using QED to calculate the the success probability of sending a pair of entangled electrons

Some procedures of quantum information technologies, such as quantum teleportation, require two parties to share a pair of entangled particles, i.e., each party has access to one of the particles, and ...
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How does a reflected photon keep its entanglement [duplicate]

I'm curious how a photon from an entangled pair, travelling through say a delayed choice quantum eraser experiment, can bounce around between mirrors but remain entangled with its partner photon, when ...
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Singularity and entanglement on surface of event horizon

An entangled pair of particles is created with one particle embedded onto the surface of a singularity. The other particle at some stated epsilon distance above the event horizon of the singularity. ...
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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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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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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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How do environment effects enhance quantum efficiency?

In a quantum system coupled with a wet environment, such as in photosynthesis (and here), how can one intuitively explain that the decoherence gives a positive effect to the efficiency? Is it ...
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Freshman-level presentation of quantum mechanics using decoherence?

Probably within the last year, I came across a recent textbook or textbook-style presentation of quantum mechanics, at the freshman level, that introduced the subject from scratch using decoherence. I ...
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A two-level system under Ito-calculus

I'm considering the evolution of a two-level quantum system given by $$i\begin{pmatrix}\dot{c}_1\\ \dot{c}_2\end{pmatrix}=\begin{pmatrix} \frac{1}{2}E & \Delta(t)\\\Delta(t) & -\frac{1}{2}E\...
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High temperature quantum effects using magnetic fields?

I have been reading some introductory material on quantum computation and am wondering about some of the underlying physics (My background is in mathematics). My biggest question is regarding the ...
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1answer
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Resource recommendation for interpretation of quantum mechanics?

The jumping of the quantum state to one of the eigenstates of $Q$ is the process referred to as state-vector reduction or collapse of the wave function (where $Q$ is an observable). I used to think ...
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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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Relating Temporal Coherence and Intensity of Interference Pattern

In trying to understand the phenomenon of coherence a bit deeper, I have come to face the following question. Suppose one uses an interferometer (Micheloson-Morley, Mach-Zehnder, etc) to measure the ...
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How do I plot the decoherence of an open system from its density matrix?

If I have a two qubit state interacting with an environment that will decohere it, how do I model the decoherence from the density matrix? For example, if I start with some state $\Psi(0)=|0>_1|1&...
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183 views

Why does MWI need decoherence theory and how can these models be combined?

As far as I understood decoherence theory, it explains, why we are not able to measure superposition of macroscopic objects in some specific basis, which turns out to be the position-basis in most ...
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What is the importance of a diagonal density matrix after measurement/decoherence?

Let $|\psi_{SA}\rangle$ be the state of a system and an apparatus, for example an electron spin and a Stern-Gerlach apparatus. If $|\psi_S\rangle=\alpha|\uparrow\rangle+\beta |\downarrow\rangle$ ...
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Question about quantum interaction [closed]

Here are some of my doubts: (there's quite a number which I couldn't find satisfying ans to, you can choose any qn to ans, thanks in advance) How close must two wave functions be to be considered an ...
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1answer
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Trying to understand decoherence… how would macroscopic objects behave without decoherence?

I've read it said that decoherence is the reason we don't observe macroscopic superpositions. I find this very confusing... what exactly does it mean to observe a macroscopic superposition? Doesn't ...