What is Decoherence: Definition and 174 Discussions
Quantum decoherence is the loss of quantum coherence. In quantum mechanics, particles such as electrons are described by a wave function, a mathematical representation of the quantum state of a system; a probabilistic interpretation of the wave function is used to explain various quantum effects. As long as there exists a definite phase relation between different states, the system is said to be coherent. A definite phase relationship is necessary to perform quantum computing on quantum information encoded in quantum states. Coherence is preserved under the laws of quantum physics.
If a quantum system were perfectly isolated, it would maintain coherence indefinitely, but it would be impossible to manipulate or investigate it. If it is not perfectly isolated, for example during a measurement, coherence is shared with the environment and appears to be lost with time; a process called quantum decoherence. As a result of this process, quantum behavior is apparently lost, just as energy appears to be lost by friction in classical mechanics.
Decoherence was first introduced in 1970 by the German physicist H. Dieter Zeh and has been a subject of active research since the 1980s. Decoherence has been developed into a complete framework, but there is controversy as to whether it solves the measurement problem, as the founders of decoherence theory admit in their seminal papers.Decoherence can be viewed as the loss of information from a system into the environment (often modeled as a heat bath), since every system is loosely coupled with the energetic state of its surroundings. Viewed in isolation, the system's dynamics are non-unitary (although the combined system plus environment evolves in a unitary fashion). Thus the dynamics of the system alone are irreversible. As with any coupling, entanglements are generated between the system and environment. These have the effect of sharing quantum information with—or transferring it to—the surroundings.
Decoherence has been used to understand the possibility of the collapse of the wave function in quantum mechanics. Decoherence does not generate actual wave-function collapse. It only provides a framework for apparent wave-function collapse, as the quantum nature of the system "leaks" into the environment. That is, components of the wave function are decoupled from a coherent system and acquire phases from their immediate surroundings. A total superposition of the global or universal wavefunction still exists (and remains coherent at the global level), but its ultimate fate remains an interpretational issue. With respect to the measurement problem, decoherence provides an explanation for the transition of the system to a mixture of states that seem to correspond to those states observers perceive. Moreover, our observation tells us that this mixture looks like a proper quantum ensemble in a measurement situation, as we observe that measurements lead to the "realization" of precisely one state in the "ensemble".
Decoherence represents a challenge for the practical realization of quantum computers, since such machines are expected to rely heavily on the undisturbed evolution of quantum coherences. Simply put, they require that the coherence of states be preserved and that decoherence is managed, in order to actually perform quantum computation. The preservation of coherence, and mitigation of decoherence effects, are thus related to the concept of quantum error correction.
1. What (property) makes a photon less likely to decohere/(entangle with the environment) relative to other "fundamental" particles (non leptons?) such as an electron?...say during single particle interference experiment
Photon single particle interference can done without the need for a...
It seems that many systems currently studied, are very fragile to dechorence. Great care is taken to isolate them from even the smallest amount of interatction with the outside environment.
Yet, the most well known quantum mechanics experiment, the double slit experiment, seems incredibly...
While reading Zurek paper Decoherence and the transition from quantum to classical -- REVISITED, he makes the statement:
What exactly is a "robust enough" correlation (from a interaction with the environment)?
I found an interesting paper
here a two level system is measured by a harmonic oscillator(the apparatus). the apparatus is coupled to its environment, a bath of oscillators.
The article shows how the reduced matrix of S+ A decoheres (the off diagonal elements tend to zero).
I am looking for a...
Books of quantum mechanics are very ambigous in this aspect. A classical apparatus that collapse wavefunction of a quantum system must "quasieliminate" the non-diagonal elements of density matrix, or have a quasiclassical wavefunction of the form
ae^{iS\hbar^{-1}} where a is a real slowly...
Yeah, the beta movement from pshycology for example, it impose that a perceptions matter in a 0,1 s (+ or -), but this need a physical explanation. The decoherence times for examle cat alive cat dead is very low than this. But we are there while decoherence. Why we don´t perceive it. The...
¿Can´t matter that decoherence matters for 2 distinct observables simultaneously ¿ Maybe the measurement apparatus must been defined clasically in this case
I know that the theoretical decoherence mechanism makes the density mattrix diagonal, but my question is if that happens in real life. I mean, let's take the hidrogen atom (lets work in the QM framework And not in the QFT framework in order to have multiple stationary states) And suppose that...
I was recently told virtual particles don't cause decoherence. Why not? Do they just never interact with their environment (apart from transferring energy/force) so they can never collapse a wavefunction?
As the Title describes, Is the measuremet problem completely solved by the decoherence Program?
In specific I would like the following question addressed.
Is there is clear explanation as to what it means to Record Infromation?
Can it explain the behaviour of a photographic plate?
What happens...
From what I have read online, decoherence is an irreversible process that gives the appearance of wave function collapse. For example, a macroscopic measuring device will always interact with the particle it is trying to measure, and the particle becomes entangled to this environment, and...
"The characteristic feature of the first (often called ‘dynamical’ or ‘environmental’ decoherence) is the study of concrete models of (spontaneous) interactions between a system and its environment that lead to suppression of interference effects"...
In principle, what is the absolute simplest arrangement to cause decoherence? In other words what constitutes a measurement? Clearly gravitational interaction is not sufficient.
Hi everybody,
which are the physical laws that make photons free from decoherence? I only read about the fact that photons have no charge, but why this implies no decoherence?
Thanks you all,
gioia
Hi everybody,
I've searched all the internet but I can't find the answer to my question. Which are times of decoherence for different physical realization of a qubit? Like, if I use photons, or spin electron, or nuclei, or ion trap, to encode a qubit, which are times of decoherence for each...
Hi all,
I've been reading the seminal Zurek papers on decoherence but there is one (crucial) point on which I am confused. I understand the mathematical demonstrations that over very short timescales the superpositions of states represented as off-diagonal terms in the density matrix can be...
Hi all,
My limited knowledge of quantum decoherence leads me to believe that it can be demonstrated experimentally via rather humble apparatus involving low power lightbulbs, a few sensors, & some plywood with holes in & some switches etc.
I was just wondering what kind of pattern you get if...
By 'Genuine Decoherence' - I mean collapse of the wave function by a theory and its mathematical equations.
If a micro system encounters a macroscopic apparatus - in collapse theories a definite state appears for both the apparatus and system, but after a tiny time since the system entangled...
Two questions regarding decoherence
1) preferred pointer basis:
Decoherence explains why a quantum object interacting with a measurement device plus environemt results in a "classical state" of the measurement device. What is the explanation for a "preferred pointer basis"and why does the...
I've read the Quantum Zeno (QZ) Effect is caused by Quantum Decoherence (QD), and that QD is, in general, a representation of the wave-function collapse of a quantum system (the Wikipedia explanation on this is confusing to me, to say the least).
If I understand the QZ Effect correctly...
I'm trying to at least understand what decoherence can and cannot explain about how quantum mechanics works, the more I read, the less clear I am about what is known and what is merely speculative.
So I finally decided the only way to get any further was to try and clarify what I think is...
Why doesn't it occur constantly and only when 'interacting" with another larger scale phase space? Why does an electron for example require a large scale human readable detector in the way to interact that way with the environment when the environment is there anyway? Air, Dust, etc.
--
Also...
I'm a physicist, but I'm not a specialist in the foundations of quantum mechanics. This month's Scientific American has an article by Vlatko Vedral about entanglement and decoherence.
Paywalled article, with a brief summary...
Hi, I'm confused by subtle differences between the concept. Let's take the example of a Schrodinger Cat. Supposed you could make a box that can isolate anything inside from say gravity, microwave radiation, is in 0 kelvin, etc. or let's just accept (for sake of discussion) that a box can totally...
I've been reading a bit about quantum decoherence today. But I'm stuck on the following contradictions:
I think I've read somewhere that after the wave function collapses, it will resume its normal superpositioned state soon after measurement. But according to quantum decoherence a...
Von Neumann wrote in a major physics book decades ago that consciousness was what collapse the wave function.. how could he stated this bizaare statement and the facts remain up to this day?
Is the interpretation been refuted already by the latest discovery of Decoherence? I can't find...
Just read a bit about decoherence from wiki, it seems to me that according to this interpretation, the probabilistic nature of QM is no different from statistical mechanics, and the irreversibility of measurement is just thermodynamic, so does this mean decoherence is indeed a deterministic...
Suppose 10,000 years from now, we perform the ultimate macroscopic superposition experiment: We're somehow able to prepare an entire star, complete with a large orbiting planet, as a pure quantum state. It is surrounded by a black shell, of radius 1 light-day, which is maintained at a...
"Decoherence does not generate actual wave function collapse. It only provides an explanation for the appearance of wavefunction collapse. The quantum nature of the system is simply "leaked" into the environment"
http://en.wikipedia.org/wiki/Quantum_decoherence
I have taken a full year of...
Hello, I would like to ask if there is a standard explanation of decoherence in the universe as a whole.
I can see how decoherence is responsible for the classical behavior of a measured macroscopic object in its environment. But what about the big picture? Is it thought that the entire...
From my understanding decoherence occurs whenever a quantum object interacts with a macroscopic sized object. So for instance a measurement involving a photographic plate registering a particle will cause decoherence of the wavefunction, which appears to us as the wavefunction collapsing...
It seems decoherence can not explain the measurement problem, but I wonder why I rarely read about the interaction between a quantum system and the environment being causal as an interpretation. What about a causal interpretation for the process of decoherence? This avoids a true collapse...
Why does decoherence not fully solve the measurement problem? I know that must have been discussed here before a lot, maybe someone can me direct to a earlier thread or post that explains it well?
I read some QM texts, but they mostly do not discuss decoherence. I know something with...
Hi, I keep confusing myself between decoherence and the transition from pure to mixed, both of which, as far as I know, come about due to the interaction of a system with the environment.
I like to think about things in terms of the density matrix to get it solid in my head.
Can someone...
In statistical physics, we have a system interacting with a (random) medium.
This is what shifts and broadens the system states and this is well understood.
Clearly the random interaction is responsible for the shift and broadening(because
if it were nonrandom, it would simply cause a...
Can the Quantum Zeno Effect be solely attributed to decoherence? In every single case?
Is the consensus on this matter opinion, or rigorously tested fact in which every case can be attributed to decoherence?
On a more well known note, can the supposed wavefunction collapse (which gives...
While I understand that the a single quantum can indeed exist in a superposition, does the interaction of various quanta exist in superpositions as well? If so, is the idea of a limit on the number of these interactions before a definite state is reached what is referred to as decoherence, and...
I am currently trying to resolve a question in my head that I am sure is covered in basic quantum mechanics but have been unable to find a clear definitive answer. Hope the forum can provide insight or direct me to a reference that would help?
Recently mechanical vibration of entangled atomic...
Hello
I am reading this book: "[URL and the appearance of a classical word&f=false"]decoherence[/URL]
I hope someone could help me.
Please go to Appendix A1
Joos introduces the notation f(q,q'). What is the dimension of f from his notation?
Next page he writes that \int f^2 d\Omega...
Here are the Pirsa video talks by Robin Blume-Kohout:
http://pirsa.org/index.php?p=speaker&name=Robin_Blume-Kohout
I've just seen one talk, that he gave October 1, just a couple of weeks back.
The topic is Quantum Knowledge.
http://pirsa.org/09100089/
What is it. What is quantum data...
So if you remember, Loschmidt's paradox is about "Loschmidt's paradox, also known as the reversibility paradox, is the objection that it should not be possible to deduce an irreversible process from time-symmetric dynamics" ( http://en.wikipedia.org/wiki/Loschmidt's_paradox )
My question is...
Decoherence may involve the minimization or constancy of states. (Physics of the Impossible, by Michio Kaku, page 248.)
Entropy involves the maximization of states. (Any statistical mechanics textbook.)
1. Does one eventually overcome the other as time approaches infinity?
2. Could there be...