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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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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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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Probabilities with the Density Matrix

The density matrix of the system is given by: $$ [\rho_{S}(t)]_{mn} = [\rho_{S}(0)]_{mn} e^{-i\omega_{0}(m - n)t} e^{-i \delta(t)(m^2 - n^2) - \gamma(t)(m - n)^2}, ...
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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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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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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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Decoherence Free Subspaces and how they stay this way, using the Zeno Effect

I am currently reading papers discussing the Zeno Effect, which discuss how measuring a system at high frequencies can almost freeze the state of a system, or keep the system in a specific subspace of ...
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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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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 ...
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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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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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What is the decoherence time scale for the most promising quantum computing implementations

I'm searching for some data about decoherence time scales for qubits in modern quantum computing implementations. The only reference I have is a table in "Quantum computation and quantum information"...
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Einselection locality in decoherence theory

Consider two polarity-wise entangled photons A and B in an EPR experiment. The process of measuring the polarization of photon A by Alice is described by the decoherence of the 2-photons system ...
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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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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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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 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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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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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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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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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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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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Simple question about decoherence

In simple terms, decoherence is the mechanism through which a quantum system in superposition that interacts with the environment undergoes a quick "apparent collapse" and is no longer found in ...
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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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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 gravity affect entanglement?

Hypothetically an entangled pair of atoms are placed inside two similar satellites orbiting at the same altitude, one of the satellite will then slow its speed and descend towards the surface of Earth....
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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?
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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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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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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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In light of quantum decoherence, are there still any “gaps” in our knowledge of quantum mechanics that need further interpretation?

With quantum decoherence, are there still any "gaps" in our knowledge of quantum mechanics that hint (either in terms of the physics, philosophy, or otherwise) at the need for further interpretation? ...
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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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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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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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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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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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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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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 ...