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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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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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Quantum physics - measurement collapsing wave functions

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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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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Are there constraints on the density matrix during decoherence?

A privileged basis emerges during measurement. starting from a pure vector state $|V \rangle$ in a n dimensional hilbert space it gives after décoherence a density matrix $p_1 |e_1 \rangle \langle e_1|...
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Loss of relative phase through ignorance and what is measurement?

Two online lectures I found by Prof. Wojciech Hubert Zurek and Nima Arkani-Hamed made me try to understand the meaning of: "It is our ignorance of the environment that leads to the loss of information ...
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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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Coherence of light after it is coupled and decoupled int0/from surface plasmon

If I excite some SPP resonantly with a laser, and then the SPP is coupled radiatively back into air, is the coherence of this light preserved?
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For a pure state, how can we use reduced density matrix instead of the pure-state density matrix?

For reference: I was reading this paper and on page 9 the author goes through the concept of reduced density matrices. $\newcommand{\ket}[1]{|#1\rangle}$ How is $Tr(\rho\hat{O})=Tr_j(\rho_j\hat{O}_j)...
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Has quantum “solipsism” been addressed in the MWI literature?

There are similar-sounding questions in philosophy SE (see here and here), but they are rightly ignored for being too vague. I will try to be more precise. There is a particle in state $|\psi_0\...
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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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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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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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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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Can someone give an intuitive explanation of how information might be 'behind everything'?

I read on the Arxiv blog (and elsewhere) that 'there is the hint in C. Fields’ ideas that information provides the ghostly bedrock on which the laws of physics are based. That’s an idea that has ...
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How did people think about the Copenhagen Interpretation before decoherence was discovered?

It seems today a lot of people are happy to think about quantum mechanics in terms of collapse theories, without thinking about where in the process the collapse occurs or what triggers it etc. This ...
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Delocalized quantum systems and gravity

Briefly, for microscopic systems be they nano-particles or electrons, that are massive (i.e. rest mass $m_r \neq 0$), we know that their behaviour is described using Quantum Mechanics (QM). Such small ...
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Can we measure without collapsing (too much) the wave function, according to decoherence theory?

According to decoherence theory, the collapse of the wave function is a continuous process due to interaction with environment. In a measure, there are interactions with photons (for example). Can we ...
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Minimal decoherence for a 3 levels system

In the case of a two level system driven by a monochromatic excitation, a minimal amount of decoherence results from the finite lifetime of the excited state. In the optical bloch equations, the ...
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How small must an object be in order for it to be subject to the laws of quantum mechanics? [duplicate]

How small must an object be in order for it to be subject to the laws of quantum mechanics?
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Can dark matter be ordinary matter in a quantum coherent state?

The hypothetical dark matter halo envelopping a galaxy looks like to a gaussian distribution of position probability density of a particle in a quantum coherent state. How long should a wave function ...
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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 ...