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.

Filter by
Sorted by
Tagged with
1 vote
0 answers
24 views

Interpreting a Density Matrix Resulting from Decoherence of a GHZ State

This questions extends on this question. What this question is about: Decoherence model. Consider a simple decoherence process modelled by $$\mathcal{E}\left(\rho\right)=p_0\rho+(1-p_0)\sigma_z\rho\...
  • 689
0 votes
0 answers
62 views
+50

Decoherence via environmental photons

I am reading the book "Decoherence and the Quantum-to-Classical Transition" by Maximilian A. Schlosshauer, and I have come to understand that for a two-level system with eigenstates $|a\...
2 votes
1 answer
94 views
+50

Dephasing noise as a decoherence model - Effect on a generalized GHZ state

Some input: Consider a decoherence process modelled by $$\mathcal{E}\left(\rho\right)=p_0\rho+(1-p_0)\sigma_z\rho\sigma_z$$ with $p_0=(1+e^{-\gamma t})/2$. One can readily find that this leads to $\...
  • 689
1 vote
1 answer
47 views

Lindblad equation from microscopic principles for free particles with momentum interactions

I'm rather familiar with the formalism of quantum master equations, but I'm struggling with deriving from microscopic principles the collapse operators for a particular case I need. I consider two ...
  • 865
-1 votes
2 answers
74 views

Why is there non-zero probability for a particle to "escape" completely from a solid? [closed]

Let's consider a particle (electron or proton) in a "macroscopic" solid. Outside of the solid, the state of the particle would have a higher energy. Because of the conservation of energy, ...
user avatar
2 votes
4 answers
158 views

Does quantum mechanics require classical mechanics for its own formulation?

Is true that quantum mechanics requires classical mechanics (as a limiting case) for its own formulation?
user avatar
2 votes
1 answer
82 views

Molecules are made up of numerous subatomic particles, so don't they constantly interact? How can we achieve quantum coherence? ($\rm C_{60}$)

Since $\rm C_{60}$ is a molecule made up of numerous subatomic particles, no matter how separated from the environment, the interaction between $\rm C_{60}$'s subatomic particles inevitably causes ...
  • 41
0 votes
1 answer
38 views

Does the inside of a solid object not interact with the outside environment? But how does quantum decoherence happen?

We have learned that quantum decoherence is caused by interaction with the environment. However, inside our body, there is no interaction with photons or air molecules in the environment, so how does ...
  • 41
0 votes
0 answers
21 views

What is decoherence important for?

Decoherence has several important applications or is important in not only one way. There is the theoretical (and now also practical) interest in the quantum-to-classical transition. There is it's ...
  • 689
1 vote
1 answer
28 views

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 ...
2 votes
0 answers
46 views

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. ...
  • 689
0 votes
1 answer
38 views

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 ...
  • 689
3 votes
1 answer
37 views

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|...
  • 689
1 vote
2 answers
85 views

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 ...
  • 1,864
0 votes
1 answer
92 views

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 ...
  • 5,665
0 votes
2 answers
135 views

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 ...
-2 votes
1 answer
70 views

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 ...
  • 41
2 votes
1 answer
62 views

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 ...
1 vote
3 answers
118 views

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 ...
  • 41
1 vote
4 answers
113 views

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 ...
  • 141
-1 votes
1 answer
60 views

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 ...
0 votes
0 answers
34 views

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?
-1 votes
1 answer
57 views

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 "...
-1 votes
2 answers
158 views

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 ...
1 vote
2 answers
171 views

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 ...
  • 11
1 vote
1 answer
164 views

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 ...
  • 41
0 votes
0 answers
39 views

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 ...
  • 41
5 votes
1 answer
136 views

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 ...
0 votes
0 answers
56 views

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\...
  • 689
0 votes
3 answers
135 views

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 ...
2 votes
1 answer
39 views

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\...
  • 689
1 vote
0 answers
50 views

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 ...
  • 689
2 votes
0 answers
53 views

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 ...
  • 41
2 votes
1 answer
140 views

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 "...
  • 689
1 vote
2 answers
263 views

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 ...
  • 689
1 vote
0 answers
84 views

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 (...
  • 689
1 vote
0 answers
65 views

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 ...
  • 420
1 vote
0 answers
26 views

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 "...
  • 689
1 vote
0 answers
38 views

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 ...
0 votes
0 answers
34 views

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 ...
  • 689
0 votes
1 answer
62 views

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 ...
6 votes
3 answers
409 views

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 ...
  • 1,177
0 votes
0 answers
52 views

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 ...
  • 11.6k
1 vote
1 answer
59 views

Is there a limit of size for superpositions?

Can objects be always in superposition if there were no environment for decoherence to occur.
1 vote
0 answers
52 views

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 ...
2 votes
1 answer
124 views

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 ...
2 votes
0 answers
61 views

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 ...
  • 425
7 votes
1 answer
276 views

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 ...
3 votes
0 answers
62 views

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 = ...
  • 689
0 votes
0 answers
77 views

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 ...
  • 1,034

1
2 3 4 5 6