Talk:Quantum Zeno effect

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dima 11:27, 18 March 2006 (UTC)


I suggest the definition:

In general, the Zeno effect can be defined as
Class of phenomena when a transition is suppressed by some interaction which allows the interpretation of the final state in terms of ‘‘a transition has not yet occured’’ or ‘‘a transition already occurred’’. In quantum mechanics, such an interaction is called ‘‘measurement’’ because its result can be interpreted in terms of classical mechanics. Frequent measurement prohibits the transition.

If colleagues agree, let us put it a the main page.

my god! mnemonic 13:31, 2004 May 31 (UTC)

I think "This occurs because every measurement causes the wavefunction to "collapse" to a pure eigenstate of the measurement basis." this is not correct. It should be "This occurs because each monitoring of the particle or system causes it to reset to its initial wavefunction" In fact the effect of a measurement in quantum mechanics causes it to collapse. However, if a quantum mechanical system collapses to one of its eigenstates, the system then becomes classical, in other words other possibilities are lost. The quantum zeno effect does not tell us that a decaying, i.e. unstable, will collapse to one of its eigenstates, it tells us that the possibility of finding a particle decayed in an interval of a time scale will decrease with the frequency of monitoring it whether it decayed or not. A continuous observation will make this possibility zero.

Sounds like original research[edit]

 The reason we can't use the Zeno effect as a science-fiction-like stasis field 
 to freeze large objects is because there is no way to couple them so strongly to 
 the environment. Ordinary molecular forces are clearly insufficient. A much easier
 way to freeze a large object would be to cool it down to near absolute zero. At
 absolute zero the system is in its ground state and there is no macroscopic 
 evolution. This is known as the third law of thermodynamics. Note that the Zeno 
 effect allows a system to be frozen into an excited state, not just the ground
 state, so in some sense it is more versatile."

Can we get some references on this? 01:02, 9 February 2006 (UTC)

I just went ahead and removed that. Now I'm wondering upon this business:
 In reality, collapse of the wavefunction is not a discrete, instantaneous event...
Where "in reality" does anyone discourse on the process of wavefunction collapse? 00:24, 21 February 2006 (UTC)

Anyone looked at this?[edit]

Practical application of the QZE. I've checked around and it doesn't appear to be anything other than what it claims.

Connection with Turing?[edit]

Apparently Alan Turing had something to say about zeno-like paradoxes. …‘the Turing Paradox’; it is easy to show using standard theory that if a system start in an eigenstate of some observable, and measurements are made of that observable N times a second, then, even if the state is not a stationary one, the probability that the system will be in the same state after, say, 1 second, tends to one as N tends to infinity; i.e. that continual observation will prevent motion. Alan and I tackled one or two theoretical physicists with this, and they rather pooh-poohed it by saying that continual observation is not possible. But there is nothing in the standard books (eg Dirac's) to this effect, so that at least the paradox shows up an inadequacy of Quantum Theory as usually presented.

Has anyone explored this connection? 02:14, 5 May 2006 (UTC)

I believe Turing invented the "Turing paradox" which was what it was referred as in the first reference in the literature. Turing two years before his death spent allot of time working on the problem of whether the mind was computable; the essential question being that of bringing quantum mechanics into a form that can simulated on a Turing machine. I believe this is eventually the problem of developing the mathematical formalism of quantum mechanics into a form that does not reference an observer. I believe it was Turing who first noticed that a quantum mechanical system's transition into another state was delayed by repeated measurement by the reduction of the quantum mechanical system's state into an eigenstate upon measurement. Turing Paradox should redirect here. Agalmic (talk) 14:56, 4 July 2008 (UTC)


We need a short paragraph about application of Zeno effect. with reference Some enhancement of a chemical reaction, or some advanced detector based on the Zeno effect..


Does this explain why the rabbit never caught up with the tortoise?

No, but it would explain why a watched pot never boils. —Długosz


The cite Petrosky offers a refutation of this experiment in Physica A 170 (1991) 306-325 is in a style, different from other cites. Could you check it and sullpy the link? dima 14:21, 7 April 2007 (UTC)


Someone might want to mention or reference in the article. I'm the author, so I don't think i should include it myself. —Preceding unsigned comment added by (talk) 05:57, 11 October 2007 (UTC)

implications on quantum suicide/immortality[edit]

woudln't this zeno effect have implications on quantum suicide for those who wanted to prove the existence many-worlds?

I mean, the person performing the experiment would be doing a continuous observation when he/she pulls the trigger, such observation would prevent the particle from decaying, and thus his/her own death, and after a few attempts the person would falsely believe that the many-worlds interpretation is correct.

It should be noted then, that the correct way to perform quantum suicide requires you to not observe continuosly while you pull the trigger, otherwise you'd get misleading results -- Vladimir

HAHAHA! That's funny, you brainwashed un-scientific quantum physics molester! HRMPFH! >:(


Somebody removed the definition

In general, the Zeno effect can be defined as a class of phenomena wherein transition is suppressed by an interaction that produces a state that can be interpreted as indicating either "a transition has not yet occurred" or "a transition already occurred."

from section Definition. Was it an accident? (No crytics of the definition above appeared, and no alternative definition is suggested.) dima (talk) 03:02, 2 August 2008 (UTC)

I changed the name of this section to "Description" as a defintion appears in the first line of the article. In my mind, the present paragraph introducing the section "Description" is a clearer statement than the muddled version above. It also has the merit of being proposed by workers in the field. Brews ohare (talk) 17:51, 3 August 2008 (UTC)
Merits are indicated in the preamble. It is good. Now the title of the section corresponds to its content. It is also good. However, the Encyclopedic article should indicate not only merits, and not only describe the term, but also define it. The definition should be as general as possible and as short as possible. I would add section Definition. dima (talk) 01:50, 4 August 2008 (UTC)
The statement:
the situation in which an unstable particle, if observed continuously, will never decay
appears to me to be a definition. Apparently you do not agree. Why not? Brews ohare (talk) 06:03, 4 August 2008 (UTC)
The 30 year old definition is too narrow. Since 1977, various colleagues applied the same term to other transitons. One may work with a waweguide, which slowly mixes the modes (for ex., rotates the plane of polarization). One can set a series of polarisers, that "measure" the polarization, preventing the rotation; and claim, that this is manifestation of the Zeno effect. Past century, Bogdan Mielnik claimed that quantum mechanics is uncomplete, because the Zeno effect means, that frequent look for a body in some region should prevent the body from entering that region. His interpretation is wrong, but his reference to the Zeno effect is correct; and it refers to the moving arrow better than the decaying atom does. Now, the "Zeno effect" may refer to ANY transition. The historical case you mention (I recognise the merit of Sudarshan) is the subset of phenomena called as "Zeno effect". (First trains were moved with steam locomotives, but one should not specify "steam machine" in definition of word "train".) dima (talk) 08:04, 4 August 2008 (UTC)
It sounds like an historical section is needed. Maybe the intro line could read as is with a caveat that further developments are discussed below? That would need some references that I don't know about. Mine are from the literature already cited. They go up to 2006 so they are current, but maybe not broad enough in scope? Brews ohare (talk) 15:45, 4 August 2008 (UTC)
I took a stab at enlarging the definition by quoting another research paper. How're we doing? Brews ohare (talk) 16:03, 4 August 2008 (UTC)
The sentence This universal phenomenon has led to the prediction that frequent measurements during this nonexponential period could inhibit decay of the system, the so-called quantum Zeno effect looks like definiiton. Do you think that it covers all cases you would call with such term? dima (talk) 22:30, 4 August 2008 (UTC)

Quadradic Time Dependance of Decay Time[edit]

"However, its probability of collapsing into state B, after a very short amount of time t, is proportional to t², since probabilities are proportional to squared amplitudes, and amplitudes behave linearly,"

from the section "Periodic Measurment of a Quantum System seems to imply that since the wave function is a function of t, the probability is a function of t^2 since hermetian operators are linear... This makes absolutely no sense and should be removed. The reason the probability of transition becomes a function of t^2 (as far as my understanding goes) has to do more with the nature of how that decay time is approximated for very small time scales. Regardless, the statement "However, its probability of collapsing into state B, after a very short amount of time t, is proportional to t², since probabilities are proportional to squared amplitudes, and amplitudes behave linearly." Should be removed. DerwinUMD (talk) 18:58, 19 November 2008 (UTC)

It is both, actually. Embedded within the argument is the notion that the Hamiltonian is a linear operator, and for short times the time evolution operator exp(-iHt/hbar) can be expanded in a Taylor series truncated to first order: 1 - iHt/hbar. This can also be thought of as a small phase angle approximation . (talk) 04:11, 25 April 2009 (UTC)Nightvid

Stabilizing Radioactive Elements?[edit]

Would it be possible to use the quantum Zeno effect (or the watchdog effect) in some way to prevent nuclei of polonium, astatine, or other radioactive elements from ever decaying at all? This would greatly expand the possible applications of these elements if it could be done (since it would effectively "add new stable elements" to the periodic table)? Stonemason89 (talk) 23:08, 29 November 2009 (UTC)


The stuff about consciousness looks rather fringe to me. Can it be toned down? (talk) 05:05, 13 April 2010 (UTC)

Agree - as far as I'm aware, neurons are quite big, in a quantum sense - I've not heard that we expect them to decohere. (talk) 10:02, 21 September 2010 (UTC)

Significance to cognitive science[edit]

Does one really need a section for this topic. I mean, it could be a separate article, pointing out the argument and counter-argument between the groups considering various hypotheses related to the significance of the quantum zeno paradox in cognitive science. Such a short description tends to confuse more than help create exposure, and in this particular case, is not much relevant to the article either. —Preceding unsigned comment added by (talk) 07:42, 14 March 2011 (UTC)

Possible inconsistency in direct and inverse proportionalities[edit]

The time it takes for the wave function to "collapse" is related to the decoherence time of the system when coupled to the environment. The stronger the coupling is, and the shorter the decoherence time, the faster it will collapse. So in the decoherence picture, a perfect implementation of the quantum Zeno effect corresponds to the limit where a quantum system is continuously coupled to the environment, and where that coupling is infinitely strong, and where the "environment" is an infinitely large source of thermal randomness.

I like the fact that this is in plain language instead of mathematics, but it seems inconsistent to me. It is first stated that stronger coupling to the environment results in faster collapse. It is then stated that continuous coupling to the environment results in completely slow, or no collapse. Can someone who knows QM please fix this or else explain why it is consistent? Exactly when do obervations/measurements delay collapse and when do they speed it? Can the half-life of radium actually be increased and decreased experimentally, as is implied? David Spector (talk) 00:47, 28 November 2011 (UTC)

A few remarks, attempting to help with regard to the above question:

  1. Strictly speaking, collapse is used improperly here. Here, it is only about decoherence, which means that the system of interest, in a superposition of distinguishable states, interacting with the environment, unavoidably gets entangled with the environment, which prevents the states in the superposition from being able to interfere later with each other. This decoherence is enough to explain that we never observe superpositions of states at the macroscopic level and that the result of a measure gives a single number, in other words you will never see the arrow of a measuring device pointing in two different directions at the same time. (The release of a single photon into the environment or the interaction with a single photon from the environment is in principle enough to get a complete decoherence of the system of interest, because of entanglement between the system and this photon). Taking this fact into account, most physicists interprete that we don't need anymore to deal with collapse because, for all practical purposes, decoherence is enough to explain that we never observe superpositions of states at the macroscopic level, ...which is also a consequence of a collapse. But decoherence does not generate actual wave function collapse (quote from Quantum decoherence), for the simple reason that mathematically they are (very clearly) two different operations. This is just to explain how it is possible that, according to this interpretational shortcut, the word collapse is used (improperly) when dealing with decoherence. This was not your question but pointing out what we are talking about could help too. The time it takes for the wave function to "collapse" should be read as The time it takes for the system of interest to get entangled with its environment, from which it would then follow without ambiguity that it is related to the decoherence time of the system when coupled to the environment because indeed we are talking about decoherence.
  2. We then agree that stronger coupling to the environment results in faster decoherence. This means for instance that if we have more photons all around in the environment it will take less time for one of these (without regard to which one it could be) to interact with the system of interest. Or it means that the bigger the system of interest is, the more quickly it will emit a photon because of thermal radiation from the system itself, even if we took care to cool it as much as we could.
  3. And now I don't understand the origin of the issue because the second half of the sentence is not from the original text (in its current state of today, at least): It is then stated that continuous coupling to the environment results in completely slow, or no collapse. Again the word collapse is used instead of the word decoherence. And instead of slow decoherence, I would have said continuous decoherence, in the sense of repeaded. And to repeat it continuously, it has of course to be fast, not slow. I would further comment saying that, without the mathematics, we are further abused by the collapse/decoherence ambiguity, because in this sentence and/or in what the writer was thinking about, other features of these concepts may collide. I mean : collapse (now taken in its proper meaning) does mean a change in the quantum state, while the Quantum Zeno effet means preventing a change in the quantum state. So, to such a point, one may say something while thinking to the opposite making use of improper terms. May be...JPB (talk) 16:18, 25 August 2015 (UTC)

A summary of the situation is provided by Davies[edit]

I don't think that the provided quotation by Davies has anything to do with quantum Zeno effect. I think it does not bring anything useful to the discussion and may be deleted. Danko Georgiev (talk) 08:44, 21 September 2012 (UTC)

Simple Question[edit]

It would improve the article if it could answer a simple question. Imagine a large lump of uranium. If a given atom decays and fissions, then it will affect nearby atoms, both by its emitted particles, and by its change in radius and momentum. So aren't those nearby atoms "observing" it, simply by being there? Shouldn't this continuous observation prevent any lump from ever being radioactive?

An answer would greatly help the reader in understanding this subject. Or, if that answer is currently unknown or debated, then that fact should be mentioned. — Preceding unsigned comment added by 2600:100D:B028:6C24:45CB:CD82:838F:D412 (talk) 21:24, 19 August 2015 (UTC)

Interpretational stuff[edit]

I have removed this reference "Koshino" from the article and I have just replaced it by a "Citation needed" because the chapter at the end of which the reference was deals only with the interpretations of QM, while in this paper (PDF available online) there is no interpretational stuff. So this reference had nothing to do there. [1]

Assessment comment[edit]

The comment(s) below were originally left at Talk:Quantum Zeno effect/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

"zeno" is very important particle. The question was raised thousand years ago, and only at the epoca of Wiki, colleagues understand its meaning and the answer. I suggest the rate "key article". dima 06:31, 24 January 2007 (UTC)

Last edited at 06:34, 24 January 2007 (UTC).

Substituted at 03:37, 30 April 2016 (UTC)

  1. ^ Koshino, K.; Shimizu, A. (2005). "Quantum Zeno effect by general measurements". Physics Reports. 412 (4): 191. arXiv:quant-ph/0411145Freely accessible. Bibcode:2005PhR...412..191K. doi:10.1016/j.physrep.2005.03.001.