Decoherence Definition and 176 Threads

As I understand it, decoherence is when the quantum system becomes entangeld with the measuring quantum system. If most of the macroscopic systems we experience are all decohered, then why do we still see quantum effects like in a transistor? Is it position AND momentum that decohere?

Does anyone know or know of the general predictions of the speed at which of coherent system losses coherence to contact with a decoherence system? Is that speed limit faster than the cosmic speed limit?

This thread is to serve as both a compilation and ground of discussion of key experiments, both historical and planned, which attempt to probe possible macroscopic limits of QM, taking into account e.g. some particular gravitational/optical/mechanical/superconducting/etc aspect and/or...

Steven Weinberg has lately been critical of QM. He now also has a technical paper out called 'Lindblad Decoherence in Atomic Clocks', available on arxiv. Here is the abstract: It's a short paper (6 pgs of text), arguing for objective collapse (a la GRW/Diosi-Penrose/etc) instead of...

Can a marble ball be considered as a subsystem of an entangled system where it is entangled with the environment? Or is "subsystem" in entanglement/docoherence only reserved for small quantum thing like electrons or photons?

In the standard mathematical formalism, the environment were treated classically, this is because observers (being macroscopic recording mechanisms) are treated classically, so the system is isolated. Decoherence is about open system, so how is decoherence compatible with Copenhagen or the...

Let's say a memory qubit inside a quantum computer is in state ## α \left|1\right>+β\left|0\right> ## This computer is equipped with a device that emits photons that carry the same qubit as the aforementioned memory location. Alice and Bob, that are very far from each other, receive and...

This paper about Quantum Darwinism https://arxiv.org/pdf/0903.5082v1.pdf starts with statement: "The quantum principle of superposition implies that any combination of quantum states is also a legal state. This seems to be in conflict with everyday reality: States we encounter are localized...

Layman question(s), but I hope not too stoopid -- many thanks to anyone with the patience to read and attempt even part of an answer, or share a possibly relevant link! I've got time today to follow and read links... 1) Saw a recent 'popular' article discussing that darn Cat as if still a...

A question about page 6 of https://arxiv.org/pdf/quant-ph/0101077v1.pdf "The second unanswered question in the Everett picture was more subtle but equally important: what physical mechanism picks out the classical states — face up and face down for the card — as special? The problem was that...

After decoherence, is there something wrong if the branch chosen would be selected by consciousness? So there is ambient consciousness that select default branches and human consciousness can bias which branches chosen? Is there any experiment that has excluded this possibility?

This thread was posted and discussed on Physics Overflow, I am re-posting it here to hear other opinions. http://www.physicsoverflow.org/36063/given-decoherence-still-random-quantum-jumps-interpretations? Environmental decoherence explains how the wavefunction of a quantum system q, as a result...

Suppose we have a pair of entangled particles. Suppose the first particle of the pair interacts with a macro-object and decoheres. Does the macro object get entangled with the second particle?

So I whilst understanding basics of some quantum phenomena like superposition, tunnelling, fluctuations etc I happened to watch the movie "Coherence" where there's a scientifically unsatisfactory reference to quantum decoherence. What exactly is this concept?

I've seen a couple of lectures by Penrose where he describes an experiment to test superposition of physical location of a very small, but macroscopic object. I can't find a reference to it online, but the experiment involved sending a photon through a half-mirror, and depending on the route...

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Hi, In Decoherence all is quantum, is there a Counterfactual Definiteness in Decoherence?

Is this statement true? >>... over the past several decades we’ve come to understand that the classical and quantum worlds don’t exactly operate by “different” rules. Rather, the classical world emerges from the quantum in a comprehensible way: you might say that classical physics is simply...

I learned that the moment a wavefunction collapse takes place is a matter of interpretation. So, I suppose the phenomenon 'wavefuntion collapse' is something that has to be witnessed by observation at some point to be able to establish it at all! So my question is: if collapse doesn't actually...

Just taking an advance in what I want to learn someday: I understand that decoherence and entanglement are more or less equivalent. So, I take it decoherence is in principle a process of entanglement. Consider two particles A and B who are entangled. if A decoheres by interacting with particle...

Hi. The Poynting vector is a 3-tuple of real or complex numbers (depending on the respective formulation of electrodynamics) times a unit. It may be pictured as an arrow with some length and direction in IR^3 or IC^3. But is it a "vector" in the strict mathematical sense, i.e. an element of a...

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 states. This can be easily seen using the projection postulate. Often the topic of decoherence...

In this paper Caldeira gives a model for the Stern Gerlach device in the vacuum. the incoming particle is described by the tensor product of a space term and a spin term a |u> + b |d> the SG is in the vacuum (no air around). Under the effect of the spatial variation of the magnetic field, there...

In the never ending quest to understand a complicated idea for which I completely lack the academic requirements to do so, I'd like to ask a few basic questions that I hope will allow simple yes/no responses (to ease the frustration of the physicist/mathematician contributors). Sadly, the...

In another thread, stevendaryl and I were trying to understand whether MWI can be formulated in the Heisenberg picture. Since neither of us really understands MWI, I tried to retreat to safer ground by asking: Can decoherence be formulated in the Heisenberg picture?

Hi guys, just a quick question. This is an idea that came up to my mind while thinking about decoherence and stability of macroscopic objects in the world. As we know all superpositions and interference effects are destroyed in a enormously tiny timescale, and as Mfb mentioned it is...

Can anybody explain what is the difference between apparent collapse and collapse? I've read that decoherence leads to apparent collapse but what does that mean, is there an eigenstate after decoherence but its not known why did it occur. I don't understand it all.

Can anybody explain this quote from stanford encyclopedia: Indeed, while it is well-known that localised states of macroscopic objects spread very slowly with time under the free Schrödinger evolution (i.e., if there are no interactions), the situation turns out to be different if they are in...

The concept of environmental decoherence has been a perpetual thorn in my brain despite an embarrassing amount of time contemplating the idea. At this point, I'm not even sure if I understand what it is purported to resolve. In many ways, it seems to me to be primarily a theory about logical set...

I was wondering about decoherence: Suppose a measuring apparatus measures a single quantum property (say, spin). After the actual measurement of the property has taken place, the result 'decoheres' into the apparatus until the apparatus shows the measurement result, after which it decoheres...

For a state |\Psi(t)\rangle = \sum_{k}c_k e^{-iE_kt/\hbar}|E_k\rangle , the density matrix elements in the energy basis are \rho_{ab}(t) = c_a c^*_be^{-it(E_a -E_b)/\hbar} How is it that in the long time limit, this reduces to \rho_{ab}(t) \approx |c_a|^2 \delta_{ab} ? Is there some...

Hi, I am an amateur enthusiast and this is a direct question (not a proposal, I'm not nearly qualified to offer a proposal). I would like to throw to experts and people who are more qualified, because it's got me a bit stumped. Could I ask for an answer which is as simple as I am please, lols -...

How do you treat decoherence in purely electromagnetic field? In other words, can EM field also have decoherence? How?

If yes, then how is it any different from other facts of causality, and why is there a puzzle? Can one not simply view quantum particle changes as the causal interaction between subatomic and macroscopic objects, yielding certain processes of behavior under physical law, depending on the...

Despite the best efforts of some of PF's finest, I continue to struggle with the general concept of spontaneous quantum state reduction by means of environmentally induced decoherence. I think that much of my confusion lies in the confounding degree of ambiguity in the delineation between the...

2 basic questions from a non-physicist (sigh!). Is decoherence essentially a measurement? And if so is the system of quantum particles set into the classical world forever? Or is there a mechanism by which it will evolve again into a superimposed state? Secondly, if the particle (as in the 2...

Hi, I've been reading some (very) basic texts on decoherence and have some questions about it: 1. What is the difference between decoherence and dephasing? 2. Assuming decoherence, can we completely do away with collapse theories (i.e. theories in which wavefunction collapse must be...

Does anyone know of QM notes (or a review article) that covers entanglement, the measurement problem, Bell inequalities, decoherence, or the delayed choice experiment (or the more recent mesoscopic experiments). So to speak the more modern and the exciting aspects of QM. I think closest to that...

If I say that decoherence is an irreversible loss of information, then in the double-slit with erasure when initially decoherence has occurred with the measurement, and then after erasure of the information the state is again as it was at the beginning , how can this occur if the initial...

I keep hearing about things like "quantum decoherence" and the notion that measurement doesn't need a conscious observer. However, I haven't really seen these topics discussed in any of the textbooks I've used (mostly on the level of Griffiths and higher). I haven't even seen a reference to...

It says here that time dilation due to gravity can cause decoherence: http://www.newscientist.com/article/dn27735-Earth's-gravity-may-force-us-to-do-quantum-experiments-in-space.html But.. wouldn't the effect of time dilation be more like a modification of the expected unitary evolution, so...

Many discussions get around the subject of how / why does decoherence happen. Interaction with the environment, getting to macroscopic scale, irreversible change of information... Somehow they seem to imply that the natural state of things in the Universe is quantum coherence and then they ask...

When photons reflect from a mirror coated with, say, an aluminium film... the reflection is presumably down to their interactions with free electrons in the metal (and each electron is in an unknown state before and after). Yet the interference does not go away if a mirror is inserted in one...

Hi fellow PFers, long time reader here. I have a query that was motivated by a comment on another thread (“Decoherence question”). It is about the quantum properties of decohered macroscopic systems. In my (incomplete and perhaps misapprehended) understanding, a macroscopic object, say a chair...

I would like to understand why is decoherence needed in QM. As I understand decoherence models irreversibility. But if two quantum systems interact and resulting states are going in different directions they can't produce interference, right? Even if they do not interact with environment. So...

So I understand that as the number of entangled particles increases, observable quantum mechanical properties decrease to the extent that the mass of particles collectively loses its wave-particle character and behaves classically. In other words, the particles' collective position-space...

It is stated that classical states are robust against decoherence.. what would happen if classical states can decohere too? Or how do you imagine it for example occurring to a table.. How would the table look like if it suffers decoherence too? Would you fall down if you sit on one?

I read up on quantum decoherence however the math was not explained clearly can someone explain it to me

From time to time I hear that Quantum Decoherence can address the measurement problem only when accompanied by deBroglie-Bohm theory(dBB) (or any hidden variable theory? or MWI?). I want to know why is that? Also, I saw some papers recently(e.g. this) that prove dBB is incompatible with QM...

When a particle decoheres, or its component states get entangled with the ``environment``, surely this is not a final eigenstate. The particle is interacting ( becoming entangled etc) with other particles and systems constantly. Therefore, isn't decoherence a continuous process?