What is Quantum decoherence: Definition and 23 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.

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  1. S

    I Electrons keeping dynamical quantum fluctuations?

    I was thinking about this paper (https://arxiv.org/abs/1405.0298) where the authors argue that there wouldn't be dynamical quantum fluctuations in a De Sitter space as fluctuations would be static once all perturbative radiation escapes the horizon (in the case that the Universe has a finite...
  2. shunyadragonvv

    I Quantum decoherence and the emergence of space/time and gravity

    Quantum decoherence. and the emergence of continuous space/time and gravity In another forum I have experienced a lot of combative dialogue asserting that continuous time/space is a property of the smallest Quantum scale. My present knowledge indicates this not true, and that the goal of the...
  3. B

    B Entangled particle decoherence question

    Suppose there are two entangled particles A and B, separated by a few miles or light years. If the spin for particle A is observed, then from my understanding, A will experience quantum decoherence. And now we can be sure that B will have the opposite spin since B is entangled with A. Assuming...
  4. Question69

    The Emergence of Classicality -- Is Decoherence accepted among physicists?

    I have tried to study decoherence theory for a while now, and it does seem to answer why classical distributions arise, instead of quantum ones.Is this fully accepted as an explanation for a classical world out of a quantum one?
  5. Question69

    B Quantum Decoherence: What Happens to Other Outcomes?

    What happens to the other possible outcomes after decoherence has been finalized? Where do they go?
  6. Auto-Didact

    A Decoherence-free phononic BEC quantum devices?

    Howl et al. 2016, Quantum Decoherence of Phonons in Bose-Einstein Condensates Anyone in the field of quantum information/quantum computation wish to comment on such an approach for building a quantum computer?
  7. Katyan Anshuman

    I What is Quantum Decoherence and How Does it Affect Quantum Systems?

    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?
  8. Quantum of Solace

    I Quantum decoherence superposition of macroscopic object

    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...
  9. Petr Matas

    What if there are no Schrödinger's cats?

    Experiment description: Let us have a slight modification of the famous thought experiment, in which the cat is killed only if a particle decay is detected in a fixed time interval, say from 0 to 1 s. Let the box with the cat, the deadly device, and the radioactive sample with the detector be an...
  10. P

    Can quantum decoherence be described as a causal interplay?

    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...
  11. T

    Quantum Quantum decoherence and measurement

    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...
  12. T

    Quantum Anti-Gravity: Exploring Coherence & Its Effects

    Am I reading some more recent articles on quantum gravity correctly that seem to be implying that a coherent particle is not subject to gravity? If you have a coherent C70 buckyball molecule (see Zeilinger - Update: "Matter-wave interferometer for large molecules", Jan. 2002), the force of...
  13. B

    Quantum Coherence - Decoherence Question

    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...
  14. Z

    Can Quantum Decoherence Math Explain Color Charge States of Quarks?

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

    Quantum Decoherence and deBroglie-Bohm theory

    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...
  16. I

    Understanding Quantum Decoherence: Exploring Its Impact on Superposition States

    does quantum decoherence mean object is leaking into the environment and actually exists permentely as a superstion of states?
  17. V

    Q regarding Quantum decoherence, r.e. double slit experiment

    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...
  18. C

    Layman's question on Quantum decoherence

    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...
  19. F

    Quantum Decoherence: Understanding Contradictions

    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...
  20. D

    Loschmidt's paradox-II: Quantum Decoherence

    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...
  21. D

    Quantum Decoherence - how fast does it propagate?

    Here, in Saint Petersburg, Russia I open a box with a Schroedinger cat I get immediately decoherenced so I see only one cat - dead or alive How soon that decoherence 'hits' you in the US? Photons can not travel directly to another part of the globe, they get absorbed/reemitted, losing the...
  22. D

    Bird's and Frog's view, Quantum decoherence and consciousness

    Hi, All As I know quantum reality (bird’s view) is transformed into the world we observe (frog’s view) via the process called quantum decoherence. Based on wiki, http://en.wikipedia.org/wiki/Decoherence (as I understand it) this is just mathematical result of mapping a quantum reality into a...