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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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 does decoherence decide which semiclassical history should happen?

As a result of decoherence, open quantum systems become entangled with each other (that is, with the environment), which leads to almost zeroing of the off-diagonal terms of the density matrix. But in ...
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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 Wigner's friend performing a quantum experiment on the rest of the universe?

In the Wigner's friend thought experiment little/no information is being exchanged between the smaller system (Wigner and his lab) and the larger system (rest of the universe). This answer has a ...
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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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the measurement problem, what is it that drives the wave function to collapse?

I'm hearing a lot of different solutions to the measurement problem. But what is the right answer? Does consciousness play a role in the collapse of the wave function or is there a different factor at ...
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What does this quantum mechanics diagram about adaptive mutations mean? [closed]

I'm a current high school student and I’m aspiring to become a biochemist. I’m at the moment writing an article about adaptive mutations but there is a lot of tricky quantum mechanics in it which I ...
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Why is decoherence considered to be a 'trick' used for practical purposes?

As I understand, decoherence consists of making the observation that when we trace out the environment from the overall density matrix of the system, we get von Neumann's projection postulate state ...
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Is the Copenhagen interpretation still the most widely accepted position?

In my undergraduate Quantum Mechanics textbook (Griffiths), of the Copenhagen interpretation it says "Among physicists it has always been the most widely accepted position". I'm currently ...
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Why doesn't decoherence spoil the double slit experiment? [duplicate]

Imagine firing one electron at a time at a double slit. Clearly the wave function interacts with the atoms of the material, and presumably many electrons do not pass through. Why does decoherence from ...
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Regarding the quantum nature of floating gate transistor - tunneling, coherence, spectrum

In a floating gate transistor, the gate is electrically isolated. I have a few questions regarding the quantum nature of this device: It is sometimes mentioned that, to store or deduct charges from ...
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What causes quantum entanglement to end?

I seems strange to me that I could not easily find information on "when quantum entanglement ends?", "What causes quantum entanglement to end?". Google search finds explanations of ...
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What is 'coherence' of a quantum system (with examples)?

The term 'coherence' is frequently used in relation to certain quantum systems such as LASER, superconductors, etc. Please help me understand what we mean by the coherence of a quantum system. How do ...
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Can someone explain the measurement problem with little bit of mathematics?

Can someone mathematize the statement of the quantum measurement problem? I am only interested in the statement of the problem (and not its solutions). Thanks. Still confused. Stated in this way (as ...
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What are fundamental reasons for conservation laws in Quantum Mechanics?

Let me be a little silly and suppose that when "God" created our Universe - he had these 3 options: (Most classical): let the energy (contained in any particle = field excitation) spread ...
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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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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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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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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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