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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How to understand the frequency picking in spin-boson model in the Born-Markov limit?

I have been reading the book Decoherence and the quantum-to-classical transition by Maximilian Schlosshauer, section 5.3.2 A classical example is the spin-boson model which has the following ...
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How do different $|\text{Alive}\rangle+|\text{Dead}\rangle$ kind of states behave under decoherence?

I am looking for literature that investigates said behaviour for spins. So far I found many papers on how to measure the macroscopicity of states and therefore a classification of macroscopic states. ...
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The quantum-measurement limit of decoherence

What this question is about: (Simple) models that show that decoherence is the reason for the non-observability of superpositions of macroscopic states use the simplification, that the Hamiltonian ...
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Vanishing off diagonals means non observability of quantumness - But aren't superposition always non observable (in pointer basis)?

Let's take a look at two states, described by $$\rho_{A1}=p_{c0}|0\rangle\langle0|+p_{c1}|1\rangle\langle1|$$ and $$\rho_{A2}=p_0|0\rangle\langle0|+p_1|1\rangle\langle1|+\sqrt{p_0p_1}|0\rangle\langle1|...
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Does quantum decoherence desctibe a deterministic universe?

QM describes a system, whose state evolve unitarily, which is deterministic. The apparent non-determinism comes from the measurement problem, where the state is projected to some subspace in a ...
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How to compute the exact universe branches in many worlds interpretation?

Many worlds interpretation says that, whenever a system's state gets decohered over time, such that no interference between the decohered states is possible anymore, the universe branches, with there ...
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Why doesn't environmental decoherence completely prevent from happening the quantum tunnelling of macroscopic objects? [duplicate]

A macroscopic object has the order of Avogadro’s number of particles. That’s over $10^{23}$. So the probability of all of them tunneling, at the same time, is on the order of that original small ...
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Isn't it inaccurate to use the Schrödinger equation to find the probability that a macroscopic object will undergo quantum tunneling?

Since Schrödinger's equation doesn't show wavefunction decay or quantum decoherence, isn't it inaccurate to calculate the probability that a person or macroscopic object will quantum tunneling? I ...
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Does pure state dephase or decohere?

I know that from the fundamental postulates of quantum mechanics, the norm of state must be preserved under time evolution. But today, I heard some mysterious comment that pure state, the state which ...
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Will quantum events ever occur on a macro-scale rather than a vacuum? Michio kaku says there's a chance we'll wake up on Mars tomorrow

https://www.theatlantic.com/science/archive/2018/10/beyond-weird-decoherence-quantum-weirdness-schrodingers-cat/573448/ In this post, it is shown that quantum decoherence in the macro world occurs ...
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Is measurement or interaction what collapses that wavefunction?

I'm very confused about what exactly causes the wavefunction collapse. I was under the impression that quantum objects propagate as waves and interact as particles. That is, upon interaction with ...
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Is there a quantum interpretation which holds that quantum mechanics completely cease to apply at a certain level?

An interpretation which holds that there is a sharp threshold between quantum objects and classical objects. If there is such an interpretation: how is the threshold itself explained in the framework ...
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At what "level" does the environmental decoherence completely surppress quantum tunnelling?

In this regard, is it possible for an extremely tiny (but still visible with the naked eye) object to perform spontaneous quantum tunnelling despite of the fact that decoherence is at work?
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Why extremely tiny (but still visible with the naked eyes) objects do not quantum tunnel? [duplicate]

What is the reason that we don't see such objects quantum tunnel? Decoherence? If YES, at what "level" does the decoherence completely suppress quantum tunnelling? Where is the "...
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Looking for proof/derivation for non-zero off-diagonal terms in density matrix as a characterization of interference

Is anyone capable of giving a rigorous derivation of why non-zero off-diagonal terms in the density matrix of a quantum system written in a spesific observable basis characterize the possibility of ...
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The collapse of Wave function isn't a physical process - but then why hasn't everything blurred into complete uncertainty?

Sabine Hossenfelder very coherently points out the "The real problem with quantum mechanics" in the following clip: https://www.youtube.com/watch?v=LJzKLTavk-w&t=583s Shortly after ...
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In real life, for a tennis ball to go through a wall, does it have to completely prevent the particles from interacting? (decoherence)

In real life, for a tennis ball to go through a wall, does it have to completely prevent the particles from interacting? What would happen if we tried infinitely in the real world, where the ...
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Do things and people in the macro world maintain a quantum decoherence? Or do you repeat quantum coherence and quantum decoherence every moment? [duplicate]

Does quantum decoherence remain uninterrupted for things and people in the macro world? Does the interaction of particles occur permanently without interruption in the macro world? Is that why our ...
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Why aren't macroscopic objects—or really the entire universe—coherent?

From what I understand, when quantum particles interact with the environment, they get entangled with it and the entanglement rapidly spreads until it's dispersed into the environment. So wouldn't ...
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2D-Random Walk or just Simple Math?

I'm looking into a problem that involves the following sum (which is commonly reffered to as the decoherence-factor): $$r(t)=\sum_{\substack{z_l=0,1\\1\leq l \leq N}}|b_{z_1z_2\dots z_N}|^2e^{-2i\...
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Is there a natural principle that forbids real wavefunction collapse?

The wavefunction evolves unitary. We can apply a unitary evolution operator containing the Hamiltonian (which shows the relation between time and energy). This evolution is smooth and continuous. And ...
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Is there a mistake in this paper when calculating the reduced density matrix (simple model)?

This question regards this paper by Zurek, Cucchietti and Paz from 2008 (DOI: https://doi.org/10.48550/arXiv.quant-ph/0611200). There the following calculation is made: $$|\psi_{SE}(t)\rangle=a|0\...
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Gaussian Decoherence - How to (mathematically) arrive at this statement?

This question regards this paper by Zurek, Cucchietti and Paz from 2008 (DOI: https://doi.org/10.48550/arXiv.quant-ph/0611200), in specific how to arrive at (12) from (10) and (11) (please see the ...
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Help me with decoherence

Recently I’ve been trying to make sense of decoherence, and my major concern is greatly formulated by a passage on the wikipedia page: “Decoherence can be viewed as the loss of information from a ...
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Coherence and superposition principle - equivalent properties?

I'd like to revisit a question I posted earlier. While I now know what coherence means (and how it can be defined) I still struggle to give an intuitive explanation that goes along with the word "...
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Quantum coherence - what is it's definition?

I stumbled across several definitions of "coherence(s)": Pade (Hyperlink) just calls the off-diagonal terms in the density-matrix "coherences" Schlosshauer (Hyperlink) says its a ...
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Von Neumann measurement - the only reasonable way to describe a measurement?

Introductory thoughts: In many books on quantum mechanics, the Von Neumann measurement process (where the measurement device is modeled quantum mechanically) is described. For example by Schlosshauer (...
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Decoherence from path integral perspective?

Suppose I computed a truly monstrous path integral of an entire double slit experiment - including the particle, the measurement apparatus, the environment, and the experimenter - in order to compute ...
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What do Paz and Zurek mean by "one-bit" measurement in Heiss' Fundamentals of Quantum Information?

In Heiss' Fundamentals of Quantum Information (2002, p. 90) Paz and Zurek look at a "One-Bit Environment for a Bit-by-Bit Measurement". At the end they say, that decoherence because of "...
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Quantum darwinism or just entropy?

Quantum darwinism is a hypothesis that some quantum states are more robust in that they are less likely to decohere under interactions with the environment. These states are "fittest" and ...
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On implications of Schrodingers Cat regarding macroscopic quantum states and decoherence

How exactly did Schrodingers Cat lead to development regarding macroscopic quantum states and decoherence? One often hears that the thought experiment was the initiator to the question, whether ...
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Evolution of a quantum system after decoherence

Decoherence leads to an almost diagonalization of the density matrix of a quantum system (in a certain basis) after an uncontrolled interaction with the environment. How does the quantum system evolve ...
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How can any quantum superposition get produced, given conservation of energy?

Imagine I have a two-level quantum system $Q$ (motivating example: a trapped-ion qubit) where there is some energy difference between the states $\vert 0\rangle_Q$ and $\vert 1\rangle_Q$. Suppose I ...
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What exactly happening in the decoherence?

I know coherence is when every wave functions in the system is in superposition, so when a measurement is made all of a sudden only 1 wave function is left. Does it means this wave function is already ...
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Is there a limit of size for superpositions?

Can objects be always in superposition if there were no environment for decoherence to occur.
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What is the "size" of a quantum particle after decoherence?

The volume of a region of space in which a quantum particle will be detected as a result of measurement depends on the laboratory measuring instrument. How does this happen in nature? After ...
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What is the relationship between "quantum coherence" and "coherent states"?

What is the relationship between Quantum coherence and Coherent States? I (almost) get the concept of Quantum Coherence when i think about it in the framework of density matrices. I also get the ...
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Relationship between Purity and Coherence of a quantum state

I know that there is an important relationship between purity and coherence. Loss of purity is often used as a basis-independent sign of decoherence. I'm not completely sold on this. I would have ...
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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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Macroscopic quantumness and decoherence

Can somebody suggest a "measure" that aims at mathematically defining a "macroscopic quantum state" which is compatible with decoherence or the thought "macroscopicity = ...
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Why do we need quantum decoherence to explain the quantum to classical transition?

Why is decoherence necessary to explain the transition from quantum to classical... If we left out decoherence, what does quantum mechanics predict about the behavior of classical objects? My point ...
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How does the interpretation of consistent histories fit with the path integral?

The interpretation of consistent histories states that different histories of a quantum particle have different probabilities, but in fact only one of them happens. If we take the trajectory of the ...
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How do Heisenberg Uncertainty and Quantum Decoherence coexist? [closed]

I have a question that's intrigued me for awhile. How do Heisenberg Uncertainty and Quantum Decoherence coexist? I know in the early days of QM, a common reaction to the measurement problem was to say ...
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Is there a classical quantum mechanics?

Some people always say that quantum mechanics can't be described by classical mechanics and that quantum mechanics works only in isolated and cold systems, but on the other hand, there are also lasers ...
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Is there a way to quantify decoherence in the Heisenberg picture?

In the usual picture of decoherence: $\bullet$ you start with a state $| \psi(0) \rangle = | \psi_{S}(0) \rangle \otimes | \psi_{E}(0) \rangle$ for the system and environment (assumed to be ...
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Relationships between elements in the density matrix

Say we have a density matrix for a spin-1 system given by: $$ \hat \rho = \left[\begin{array} A \hat \rho_{00}& \hat \rho_{01} & \hat \rho_{02} \\ \hat \rho_{10} & \hat \rho_{11} & \...
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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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