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Quantum Measurements Leave Schrödinger's Cat Alive
First time accepted submitter Walking The Walk writes "Your co-workers who keep using Schrödinger's cat metaphor may need to find a new one. New Scientist reports that 'by making constant but weak measurements of a quantum system, physicists have managed to probe a delicate quantum state without destroying it – the equivalent of taking a peek at Schrodinger's metaphorical cat without killing it. The result should make it easier to handle systems such as quantum computers that exploit the exotic properties of the quantum world.'"
The SchrÃdinger's Cat I bought from Think Geek keeps dying half the time.
and extremely pissed off about your experiment.
http://afternoonsnoozebutton.com/post/9395842065/breaking-news-schrodingers-cat-is-alive-and
Except for ending slavery, the Nazis, communism, & securing American independence, war has never solved anything.
Why is it equivalent of peeking without killing it ?!
The cat might already be dead when you peek. Now, apparantly you simply can peek at the cat's state.
I think you missed the whole point of the thought experiment. No, the cat is decidedly not already dead when you peeked. It is the moment of your peeking that picks a state for the cat.
Which, of course, means that the summary is meaningless. I'll go read TFA, and, more likely, then consult with a Physics Phd I know to try and make (relative) sense of this discovery.
Shachar
Does anyone here RTFA?
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So, in essence, the main thing they found out is how to do more stuff with qbits without triggering a collapse of the wavelength function.
Real summary:
Obscure need which is somehow quantum computing, but not in any way feline, related gets obscure advance.
Shachar
What? Isn't the proven destructiveness of measuring a quantum system the bedrock of quantum key distribution?
You're welcome.
This is the equivalent of weighing the box. By not opening the box you don't collapse the wave function. Instead you measure some other property that is independent of the wave function. It is nothing like peeking in the box, nor does it gain any information from the wave function.
I think perhaps you may be the one confused. The point of the thought experiment is that you cannot know whether the cat is alive or dead before opening the box. It's 50/50. In one interpretation of quantum mechanics that means that the cat exists in a combination of both states prior to observing it. Observing it causes one or the other of the states to prevail.
If the cat isn't dead now, it will be eventually. So you might as well assume it's dead and move on.
Can we PLEASE call it a Heisenberg Compensator?
I had a sucky sig.
Stargate SG-1 finally got some science right!
Every time they take a peek, God kills a kitten.
I always wondered why the cat didn't qualify as an observer to begin with.
Sheesh, evil *and* a jerk. -- Jade
just long enough to be eaten by Pavlov's Dog
Nobodies Prefect
Tidbits for Techs Technology Blog
Rather than using small fury creatures with no propensity for entangled behavior, why not use something of similar size, but a bit more gracious and flat? For this I propose the noble sock - an item exhibiting (when in certain steel chambers) extremely random tendencies of existence and non-existence. We all know damned well what to expect of a cat run through a permanent-press cycle. However, no one, not even Martha Stewart knows what to expect of the sock - that ambiguous textile for which any state even science cannot predict.
Forward! -- Emperor Norton, 2012
More chinks in the armor of the abominable Copenhagen Interpretation. Bohr, Heisenberg and Schreodinger were very smart people, but they couldn't be right about consciousness affecting physics. That's just stupid.
The New Scientist frequently makes quantum leaps in logic. Or was that logic leaps in quantum physics? I GET SO CONFUSED! At any rate, the real article is a bit less sensational.
http://www.nature.com/nature/journal/v490/n7418/full/nature11505.html
No, that is not the experiment's point. That is its premise.
It is the only interpretation that I am aware of (though its precise phrasing varies). In fact, it is the only reason that anyone hopes qbits will work. Hence me not being confused.
Unlike what the original poster said, the cat is not already dead when you open the box. That is the whole point of the experiment. The cat is neither alive nor dead until the point in time in which you look, at which point it has already been alive/dead all along.
This principle is the one that drives the quantum computing research. The idea is that you create 512 qbits signifying a number. Since they are in their base form, they each can be either 1 or zero, which means that they are, potentially, all 2^512 possible numbers. You then pass them through a series of filters that, essentially, force them to multiply with another set of 512 qbits and form a known result. Only then do you check what each of the qbits is. You have just factored a 1024 bit integer in zero time by letting quantum mechanics test all possible combination concurrently.
Shachar
AFAIK it does, which is why this experiment wouldn't *actually* work. From what I have gathered about the topic, an "observer" is any VERY-many-particle system (read: billions of billions of degrees of freedom) that interacts with the quantum system. Introdouce that many degrees of freedom and the superposition is gone.
Not exactly. A cat in such a situation would of course be dead or alive, regardless of whether you observe it or not. You may not know *whether* the cat is alive or dead, but you know *that* the cat is alive or dead. The measurement of the state to choose whether or not to kill the cat would in itself collapse the waveform.
Schroedinger developed the thought experiment to describe what he considered the absurdity of the Copenhagen interpretation of quantum mechanics. It's not meant to be taken as literally as it is tended to be.
No. You cannot measure whether the cat is alive without causing a determination of that very question. You can measure other things, though.
I should point out that the cat analogy is not a very good one, and TFA chose it only to make the article more appealing.
Shachar
But weighing the box won't tell you anything (no, a cat's soul does NOT weigh 21 grams). I think it's more the equivalent of smelling the box.
There are a lot of replies that seem to be missing it. If you measure quick enough after closing the box with the cat in it, the chances of it being dead versus alive are not 50-50. Since it was alive when you closed the box, there would be a really high chance it is still alive when you peak if you peak much quicker than the halflife of the decay process that is supposed to trigger the death (for the version that uses a decay particle as the source of chance). Since this peeking collapses the wave function back from a 99-1% split back to 100% alive state, you can keep doing this to keep collapsing it to the alive site with very high probability. In the right conditions, you can go from what was a 50% chance of it being dead after a certain amount of time, to a vanishingly small chance if you can keep measuring quick enough. The actual states of a cat are much more complex, but there are two state quantum systems that take a certain amount of time to evolve into a superposition of both states.
Not exactly. A cat in such a situation would of course be dead or alive, regardless of whether you observe it or not. You may not know *whether* the cat is alive or dead, but you know *that* the cat is alive or dead.
The experiment doesn't work, so you are right. But had the experiment worked, then that claim would be incorrect. The point in time in which the universe decides whether the cat died or not is when we test it, not before. If we never test the cat, it is neither alive nor dead.
The measurement of the state to choose whether or not to kill the cat would in itself collapse the waveform.
Exactly. It is uncollapsed before the measurement.
Schroedinger developed the thought experiment to describe what he considered the absurdity of the Copenhagen interpretation of quantum mechanics. It's not meant to be taken as literally as it is tended to be.
But that interpretation prevailed. That is the whole point of ESR. It is not possible to extend a wavelength function, uncollapsed, to the size of a cat, but when actual atoms are involved it really is the point of testing that determines the result. The result is not there all along, just waiting to be measured.
Shachar
From the abstract:
"The act of measurement bridges the quantum and classical worlds by projecting a superposition of possible states into a single (probabilistic) outcome. The timescale of this 'instantaneous'process can be stretched using weak measurements usuch that it takes the form of a gradual random walk towards a final state. Remarkably, the interim measurement record is sufficient to continuously track and steer the quantum state using feedback..."
The way I read this, they aren't claiming they prevented collapse, nor that they can predict which state it will collapse to; rather, they have (1) increased the time of the collapse of the wave function (via feedback) and (2) been able to "watch" the electron collapse to whichever state it goes to. [N.B.: I am totally open to correction. I haven't paid the $32 for a copy of the paper.]
So, no Heisenberg compensator here.
"Don't blame the log for the fire." --Andrew Ratshin
It's 50/50. In one interpretation of quantum mechanics that means that the cat exists in a combination of both states prior to observing it. Observing it causes one or the other of the states to prevail.
It is the only interpretation that I am aware of (though its precise phrasing varies).
There are many other interpretations. The one where it exists in a combination of the possible states is the Copenhagen interpretation.
Another popular one is the many words interpretation. Instead of the cat being in a combination of the possible states, there are multiple universes with each universe containing a different possible history (dies at T=1, dies at T=2, still alive, etc.) and there is a different version of the observer in each universe coming to a conclusion based on which universe he's in.
In the relational interpretation observer 1 could take a peek, and know the cat is dead, while for observer 2, who hasn't peeked, the cat is still in both states.
In the ensemble interpretation the cat is definitely either alive or dead, you just don't know which before making the observation. The probability distribution does not apply to a single cat, but rather to an ensemble of cats. Repeat the experiment 1000 times and you'll get about 500 alive and 500 dead.
Unlike what the original poster said, the cat is not already dead when you open the box. That is the whole point of the experiment. The cat is neither alive nor dead until the point in time in which you look, at which point it has already been alive/dead all along.
That interpretation is different from "the only interpretation [you] are aware of." As I said above the interpretation Schrodinger was discussing has the cat in a combination of both states. Not that it's not in "neither" state. It's in a combination of them. The AC above was pointing out that you might not be keeping the cat alive while peeking. You might be peeking while keeping the cat dead. Or as the article rather than the headline actually says, you get to peek and keep it in the superposition without collapsing it.
the p -value of their "weak measurements" was 0.5
Set your phasers on "funky"!
It is the only interpretation that I am aware of (though its precise phrasing varies).
That is the Copenhagen interpretation. There are several others: In the many-world interpretation, there are universe in which the cat is alive, and universes in which the cat is dead. Until you open the peek, you can interact with both. Ones you have peeked, the versions of you in the universe where the cat is dead and the versions of you in the universe where the cat is alive diverges, and cannot interact anymore (roughly). Then there is the de Borglie-Bohm interpretation, where the cat is either dead or alive (particles have a definite, deterministic position), but until you have observed it, you can only interact with the wavefunction, which is the same for dead and alive cats (I think, but I might have horribly misunderstood it). In fact, there a quite a lot different interpretations of quantum mechanics
In fact, it is the only reason that anyone hopes qbits will work.
Qubits works because of quantum mechanics, that is, because the equations are as they are. That have nothing to do with the interpretation, which is how we understand the equations. Interpretations are not scientific, as they make exactly the same predictions as the underlying model, but are more complex. They are not really needed, but the human mind doesn't like thinking in equations, it prefers to have something that behave like something physical, so we like having them.
I think you missed the whole point of the thought experiment. No, the cat is decidedly not already dead when you peeked. It is the moment of your peeking that picks a state for the cat.
The worst ever "thought experiment" by far is Schrodinger's cat. To say a living cat was ever in a superposition of alive or dead is wrong and stupid. These words only confuse people unecessarily.
No cat was never a participant in any coherent quantum system only the measuring device which **triggers** death of the cat had anything to do with the quantum system.
Asking if a tree still falls in the forest if nobody sees it is about as instructive as the cat in the box analogy.
Which, of course, means that the summary is meaningless. I'll go read TFA, and, more likely, then consult with a Physics Phd I know to try and make (relative) sense of this discovery.
Nothing at all has been "discovered". All they did was physically implement something for which the properties have been calculated and well understood for many many decades.
The point of the cat thought experiment was to show the absurdity of taking QM at macro level.
C. Sagan : A demon haunted world:
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visit randi.org
The point in time in which the universe decides whether the cat died or not is when we test it, not before. If we never test the cat, it is neither alive nor dead.
Uhm.. No? The point in time the cat died is exactly that point in time, whenever we test it? If we never test the cat, it's *either* alive or dead..
Excellent question...I have thought much about it, as it used to be my job. Two electrons entangled in a true quantum state would be a perfect communication device...any change to the state of one would instantly change the other in the same way regardless of distance
In that **truly quantum** scenario, we would indeed have quantum signal transmission at a rate of 1/1...faster than the speed of light...instant over any distance...
That's **kind of** a big deal...Einstein called it "Spooky Action at a Distance"...it's definitely theoretically possible...and it definitely would turn particle physics on its head...and it most likely won't happen b/c the energy required to do it is probably equal to all the energy in the universe according to known science. (if you balance out the equations)
That's why I cringe every time I see 'quantum' used in reference to computing...its just marketing terms for a faster processor at this point
Thank you Dave Raggett
Does anyone here RTFA?
Of course! It's about scientists no longer using sledgehammers to check for the existence of cats in a box. Instead they shine a torch inside. Quite obvious really!
Science advances one funeral at a time- Max Planck
In one interpretation of quantum mechanics that means that the cat exists in a combination of both states prior to observing it.
The only thing in any sort of superposition is the measuring device. The hammer which breaks the beaker of cat poison, the beaker breaking and the cat dieing are not part of the superposition. They are all separate events but whatever it all sounds much better if you make mystical claims.
Observing it causes one or the other of the states to prevail.
No it is "disturbing" not "observing" ... just more unecessary mysticism to make understanding basic ideas seem more difficult than they actually are.
Unlike what the original poster said, the cat is not already dead when you open the box. That is the whole point of the experiment. The cat is neither alive nor dead until the point in time in which you look, at which point it has already been alive/dead all along.
The Copenhagen interpretation of quantum mechanics is what made Schrödinger come up with that thought experiment to begin with. It is also what made Einstein say that God doesn't play dice with the world. (he was a firm believer of determinism.)
The cat thought experiment was Schrödingers way of being a bit of a sensationalist (I guess that is why the idea got so much publicity.) in that the claim is that if we follow the Copenhagen interpretation and say that the particles are in all possible states before measurement, even if we are just talking about a single particle, we can quickly get a situation where we can no longer differ between life and death. Obviously this is silly, the cat can't be both alive and dead, instead Schrödinger would have preferred an interpretation where the state just is unknown rather than all states at once.
If the state of an entangled set of quantum bits can be known in advance and their states observed without collapsing them, then it stands to reason that a remote communications station with a pre-delivered set of pre-entangled bits could receive a message by observing the collapse the instant the 'transmitter' causes it to happen.
I wonder if this research provides this possibility, or if there is something inherent to the entanglement/observation process that prevents this.
I very gently opened the link and found that
it kept changing. At best it seems to be a
suggestion that perhaps maybe the cat has
whiskers that wiggle. As long as I look gently
on a windy day the whiskers could be wiggling because
it was alive or the wind was blowing.
Even the Google ads kept changing.
I think Google could be a cat killer if the
quantum bits was a Google search engine.
Truth is stranger than fiction, but it is because Fiction is obliged to stick to possibilities; Truth isn't. Mark Twain.
Does anyone here RTFA?
Yes, I did. The summary quotes this part line by line: "physicists have managed to probe a delicate quantum state without destroying it – the equivalent of taking a peek at Schrodinger's metaphorical cat without killing it."
This shows a fundamental misunderstanding of the cat experiment, in that the author is assuming that by opening the box the cat gets killed. When in fact the cat can be considered both alive AND dead while the box is unopened, and if you open it it might very well be alive and not dead. Thus it would be equally accurate (or inaccurate, rather) to say "the equivalent of taking a peek at Schrodinger's metaphorical cat without making it LIVE."
And to be even more nitpicky, it does alter the quantum state- it changes the oscillation but does not destroy the superposition. They also have (simply put) found a way to return the oscillation to the pre-observation state within a relatively small timeframe.
So yes, the parent's "???" was justified as the use of the analogy was horrible incorrect.
Meh, it's already been done experimentally
Have a look at the Quantum Zeno Effect which is both one of the scariest and most awesome pieces of experimental quantum physics around. Just in case your Google is broken, the experiment stops the random decay of unstable particles by continually measuring their state. Since the cat is just an allegory for these sorts of particles, the experiment has already been done - yes you can prevent a random (quantum) event by taking continuous measurements.
You don't need this thought experiment any more - as *real* physics cruised past these mind games decades ago.
politicians are like babies' nappies: they should both be changed regularly and for the same reasons
Quantum Measurements Leave Schrödinger's Cat Alive
Shouldn't that be "Quantum Measurements Leave Schrödinger's Cat In A Superposition Of Alive And Dead"? If it's decidedly alive then the waveform has collapsed, and isn't that what they're avoiding? (did not read TFA)
systemd is Roko's Basilisk.
Schrödinger's cat has surely died of old age by now.
Guvf vf abg n EBG zrffntr
This shows a fundamental misunderstanding of the cat experiment, in that the author is assuming that by opening the box the cat gets killed. When in fact the cat can be considered both alive AND dead while the box is unopened, and if you open it it might very well be alive and not dead. Thus it would be equally accurate (or inaccurate, rather) to say "the equivalent of taking a peek at Schrodinger's metaphorical cat without making it LIVE.
I'm not a quantum physicist but If I understand Schrödinger's experiment correctly (feel free to reeducate me), the cat is both alive and dead until you open the box and 'fix' it's state. Until you observe the cat all you can say is that the closer you get to an hour (the radioctive matierial decays one atom per hour) the more likely it is that the cat is dead. So have these scientists managed to observe Schrödinger's cat in it's dual live/dead 'flux' state?
Only to idiots, are orders laws.
-- Henning von Tresckow
No, you're just wrong...and you actually agreed with me when you said, "...will never happen."
See, you really need to read up on 'Action at a Distance' because it is *exactly* the phenomenon you, I, and particle physics thinks will not and cannot happen...
Yet, Einstein himself identified it as predicted in his models....seriously look it up
Thank you Dave Raggett
These interpretations all are similar in their measurable outcomes. That's why we have these interpretations instead of focusing in on one of them.
The many worlds postulate, for instance, doesn't split the universe into many until the observation is made. So the cat is in a multi-state until that point in time. In all the interpretations, there is a multi-state until the measurement is made and then something happens, depending on the interpretation.
Geordi La Forge
If you think someone isn't free to have a different definition of "freedom" you may be a tyrant.
If the cat was just either dead or alive (according to whether or not the gun, or poison or whatever was triggered by some beta decay) and we would just be unaware of it until opening the box
What would be wrong about it ?
You put a coin in a box, shake the box. surely, it is either head or tails, you just know what it is when you open the box
So why do you think there is such a buzz around the Schrödinger’s cat ?
Precisely because, the experiment is setup so that the cat is not either alive or dead, but in a special state
Schrödinger put together this thought experiment to show how silly the Copenhagen interpretation was (to his eyes)
The experiment is there to say "according to you, the cat is both dead and alive (which we can all agree on is ridiculous)"
Except it's not that simple, and then, there is entanglement and there indeed are "weird mixed states"
According to Quantum_decoherence, there is no superposition of quantum states. As the radioactive element interacts with the cat and the box, its decoherence time becomes very short, so the wave function collapses almost instantly. The cat is either dead or alive, but there is no extended state of superposition.
The cat is alive or dead and not ever in a state of superposition.
The example was (I hope intentionally) chosen to illustrate how poorly our macro world and macro thinking fail at the quantum level.
If you have any doubt of this and are romantically tied to the "alive and dead" cat, consider this: The cat is capable of making an observation. It is a complex collection of moving parts. If the parts stop moving, that is an observation.
It may be the case that quantum states on small particles do not have any internal world. That is a large area of discussion in physics. Is quantum mechanics the result of a hidden (to us) world that follows reasonable laws, or is it just very weird all the way down.
Looks like knowledge of the quantum state does not lock it in place, then.
So have these scientists managed to observe Schrödinger's cat in it's dual live/dead 'flux' state?
They must work for the Umbrella Corporation.
Does this method of observing really change anything? To me, it doesn't unless they can actually measure it, find it dead, measure again, the find it alive. If the observation is still fixing the state, in what way does this help? I will add here that I an not a quantum physicist,I did not RTFA, and it's 06:00. (That sounds like the SlashDot equivalent of that line towards the end of the "Blues Brothers").
Someone enlighten me: Have we just cracked quantum cryptography?
Could be worse. Could be raining.
They are not really needed, but the human mind doesn't like thinking in equations, it prefers to have something that behave like something physical, so we like having them.
Exactly. A workable interpretation would be that since the equations work that the world is in fact just those equations. Values are simply undefined until you plug in the values for the other variables.
But we're evolved to our experience of the real world, so want the real world to be 'real' and equations only to describe how the real world worlds, not be it. So we reject that idea instinctively.
The headline was a bit misleading. You still can't measure a quantum state without having its superposition collapse to what was measured. If I understand what the article is saying properly, these scientists are not able to peak into the box to measure "Schrodinger's Cat's" state of aliveness, but they can still peak to see if the cat is a tabby or a calico. If fur pattern isn't a good quantum number, then that will cause the "cat" to change its spots, but later probes can be used to nudge it back to its original state. Meanwhile, you haven't disturbed the "cat's" aliveness or deadness. The important part seems to be being able to "nudge" certain states with probes to get some information out of the system without really changing it.
The Schrödinger's cat is just great marketing for a very straightforward statement. The cat is alive (cat = 1) in 50% of the worlds, the cat is dead (cat = 0) in 50% of the worlds, but you don't know in which world you are until you look at the cat (a.k.a. "collapsing the space of probabilities", big marketing words for a straightforward concept). Schrödinger's merely says that the cat's expected value is: 0.5 * 1 + 0.5 * 0 = 0.5 (but this is a statistics mean, doesn't imply that the cat is both alive and death, just like families never have 1 kid and a half)
The correct way to say it, is that schrödinger's cat is a projection in 3D space of a 4D space problem, where the 4th dimension is the set of "alternate scenarios", and the cat's value at a certain position, is its expected value in that position (a "fuzzy variable").
While you can't get worthwhile info from studying a single cat system without "opening the box", you can discover a lot from a system with many cats; for examples, take a look at nonograms.
My dog suggests that this should be tested with a very large number of cats, and a big lump of polonium in each box.
From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
Until the Manhattan project politicians didn't see the need for fundamental physics research. (Winston Churchill being a notable exception). As the nuclear industry becomes, basically, about as exciting as the coal mining industry, the perception of the need recedes. We are back to trying to invent military uses for pure research. But if the monkeys hold the keys to the banana plantation, I think we are justified in pulling wool over the eyes of the monkeys.
From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
""The probability distribution does not apply to a single cat, but rather to an ensemble of cats. Repeat the experiment 1000 times and you'll get about 500 alive and 500 dead.""
The whole point of these experiments is to front the whimsical idea of someone, somewhere performing them 1000 times. "What did you do today, honey?" "Number 782." "Alive or dead?" "I'd rather not discuss it." "Oh really--does that mean this cat is in an undetermined state?" "Yeah--for you, now shut up and pass the peas."
Or you go to your doctor and she says, you have a 50 per cent chance of survival for the coming year. Oh shucks, you say, does this mean I'm going to have to crawl into a stupid box and wait? Who is going to open the box? What if no one opens the box? What if someone buries the box? Does this mean that in the last minute I am slightly more statistically dead already? Can I pay you in a year? "I rather you paid now." Oh, that means zero chance for survival.
According to statistics, one 30-millionth of 'you' will perish in a commercial airline accident over the course of your lifetime. Just a few cells here and there, yet something to brush off lightly.
If you've had a brush with death, do not use it on your cat.
95% of lawyers give the other 5% a bad name.
A casino is the box experiment in our reality. So long as you have money are playing you could yet still be someone and not some compulsive irresponsible bum. Here sir, have an hors'd'oeuvre. Take this chit to the bar for a free undetermined-state drink. As the evening wears on and your money is gone and you're just roaming the aisles trying to look like you lost something and the men in suits are following you discreetly and whispering into their armpits, the world outside can only observe you in an undetermined state. Then the box opens itself and you are chucked out and the experiment concludes.
50% of this message is bullshit. The other half is hors'd'hooey.
It follows from the formulation of Quantum Theory. The state of any system can be described by a superposition of, one of more, state vectors. The cat's initial state can be described as a superposition of the vectors associated with its final states: Alive and Dead.
Who ordered that?
Qubits works because of quantum mechanics, that is, because the equations are as they are. That have nothing to do with the interpretation, which is how we understand the equations. Interpretations are not scientific, as they make exactly the same predictions as the underlying model, but are more complex. They are not really needed, but the human mind doesn't like thinking in equations, it prefers to have something that behave like something physical, so we like having them.
The equations are derived through observation of physical reality. The equations are a construct of our minds that allow recognized patterns to provide predictions of physical reality. The interpretations are arguably more accurate than the equation, as they can possibly identify conditions the math has yet to be 'adjusted' to account for. To discount the source of these equations - our perceptions of the universe - is foolish.
Aren't you confounding interpretations with observations? Interpretations are interpretations of what the equations say, so they can't be more accurate than the equations. I am not discounting the interpretations, they are extremely helpful in making us understand what the equations say, and wondering about them might give rise to new hypothesis, which can be tested, but that doesn't make the interpretations themselves scientific.
I believe that the idea is that by peeking, they can see one reality, but, since they didn't technically cause one reality to collapse, they can peek again and then the outcome has a 50% chance to have a different outcome.
The cat can be in three states: alive, dead and bloody furious.
No, you don't get to peek at the cat's state. You can peek at some other property, like how fast it's transitioning between (quantum) states, but you can't see the cat's state.
To use the analogy of the thought experiment, maybe you could peek in the box and determine whether there is a cat in the box at all, or what colour it is, but if you look long enough to determine whether the cat is alive or dead then you'll destroy the superposition.
When I read the summary I also immediately thought of the quantum Zeno effect, but it's a different phenomenon.
In the quantum Zeno effect, you're preventing particles from decaying by constant measurement (and therefore causing the wavefunction to collapse).
Here, you're observing particles without destroying the wavefunction.
I, for one, think the entirety of the above conversation should be modded "Score:5, Fucking Bewildering;" who's with me? :)
That doesn't make sense. The equations of quantum mechanics describe the world, they don't create it (otherwise the world would only be a century old). We've found equations that work, but just like any equations they only tell us what's happening, not why. Newton's or Einstein's equations or the ideal gas law are no different.
If it remains in a quantum state, then it's remaining in a "random" state. If you peek and see "dead", you have a 50% chance to peek and see "alive" next time. If you peek and see dead, then keep seeing dead, then you know you have collapsed the state.
My understanding anyway.
We only managed a quick peek, but the cat is definitely dead. Or asleep. We think.
> the equivalent of taking a peek at Schrodinger's metaphorical cat without killing it.
I'll believe it when I see it.
Oh, wait.
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
No, this is not the quantum zeno effect. The experiment in the article is about quantum weak measurement. The idea is the measurement does not return the maximum possible (or as I will call it "full") information about the system, and since full information is not extracted, the state is only partially disturbed by the measurement. The quantum zeno effect, on the other hand, involves full measurement and complete state projection to keep the state from evolving. These two topic are rather different.
Of course, quantum weak measurement has also been done. Irfan Siddiqi at Berkeley recently used it to perform a quantum feedback circuit. And it has been done in different forms for the last 10 years around the world. The difference in this article is that the state being measured is what is known as a "cat state". A cat state is a state that has many particles with strong mutual entanglement. The entanglement makes the state very fragile to measurement, as measurement of any one particle will destroy the state.
So it is more like they are checking the cat's box tor signs that the cat is still alive?
No brain, no pain.
... isn't that determining the state? The purpose of the cat experiment was to state that it is both alive and dead until observed to be one or the other.
And for that matter, opening the box does not kill the cat, it just allows you to observe its state. We know that when you open the box there is a set probability of the cat being dead.
Damn_registrars has no butt-hole. Damn_registrars has no use for a butt-hole.
Your scenario presumes the cat is alive *or* dead.
I thought this too for a long time, it's only since I recently started reading more on quantum mechanics and the truly baffling experiments that have been done, that I started to understand (or is that, started to confuse) more. In fact, the metaphorical cat is both dead and alive at the same time. It is not in an unknow-but-determined state already. Observing it does not show that it was already dead or already alive. Observing it makes it fall into one of those states.
"But that makes no sense"
Yep, and it's still hurting my head too...
Of course, this might change all that...
Jeeze, I'm really starting to think that most people just shouldn't ever talk about Quantum, there's so many misconceptions and misunderstandings that trying to give people a little bit of information, since its so wildly out of context, even in the wrong context (misconceptions), that it only drives them further away from the truth, from reality. People latch onto the wrong points.
I barely understand Quantum Physics myself and I can tell that TFA makes all kinds of wild leaps in logic. Most of these things aren't true, and the way they explain the Schrodinger's Cat experiment makes the classic misunderstandings.
The reality is far less sensational: http://www.nature.com/nature/journal/v490/n7418/full/nature11505.html
GCS/MU/P d- s:- a-- C++++$ UL++ P+ L++ E+ W++ N o K- w--- O M+ V- PS+++ PE Y+ PGP t+ 5- X R++ tv+ b++ DI++ D++ G+ e++ h-
The true state of the cat is that it is not dead yet.
It is not alive in any functional way since like a good cubicle minion it is not interacting with anything outside of its box. And sooner or later it will be dead, for that is the eventual fate of all cats and minions. But since it is possible that the box may be opened somehow before the inevitable death, even though it is not functionally living at the moment we cannot say it is truly dead yet.
There is an equivalent situation in USA Presidential politics right now. At this moment whether Obama or Romney wins the election depends on whether a small number of undecided registered voters come out of their 'don't give a damn' boxen and participate one way or the other. An interesting thing is that this small number of Schrödinger's voters are influencing millions of dollars of campaign expenses. Enough to fund the teacher's salaries for a small city for several years. Enough to pay for the implementation of meaningful election reform on a nationwide basis. Enough to pay the salaries and perks that the USA Congress critters have given themselves for a day or two. Truly a great deal of money.
The implications for quantum engineering are great, but unfortunately this slashdot comment is not large enough to contain the explanation.
Will
because then you wouldn't get zombie cats.
Many worlds does not get you away from quantum superposition, because the different histories still have to be able to interfere to be consistent with the equations. My understanding of the many worlds interpretation is that when we open the box, our state becomes correlated with the state of the cat, so that the system goes from outside scientist observing a closed box containing a superposition of live cat and dead cat, to a superposition of sad scientist observing a dead cat and relieved scientist observing a live cat. In a sense, the superposition appears to go away because we become part of it. So this is a method of obtaining information about the nature of the superposition inside the box without ourselves becoming correlated with the individual states.
it is more like they are measuring the color of the cat's fur, but don't know if it is alive or dead.
and there seems to be a another consequence of this experiment, if the superposition state is collapsing, they are able to nudge it back into a superposition.
I think it makes sense. You have something oscillating between states 0 and 1 like a teeter totter with evenly weighted people on either side. The act of measuring the state is like introducing a weighted ball to the fulcrum point. Which ever side of the teeter totter is closest to the ground will have the weighted ball roll towards it thus fixing the teeter totter in that state.
Two of my imaginary friends reproduced once
But weakly observing it can have value. It would be possible, for instance, to determine whether there is a cat in the box at the moment (perhaps by weighing the box and comparing the finding with a predetermined minimum-weight-of-cat value). This is important because a cat that is not observed in any way may or may not be in any particular place. Anyone who has ever lived with a cat knows this. People who have never been owned by a cat may be incapable of understanding this, and probably should not look for a career as a quantum mechanic.
But that explanation might be too subtle for classical physicists (who likely do not much like cats, ever since Schrödinger soured them on the cute little beasties). So for them the dilemma can be stated in a more gross fashion: how can you even know whether a cat in the box is a part of the device you are trying to build unless you at least look at whether a box is or is not present? It would seem that some degree of weak observation is indeed necessary if anything is to be done.
The underlying problem is of course that quantum mechanics sits in the intersection of physics and semantics. It is not only the case that classical physics is unable to handle what is happening at the quantum level. It is also the case that as a product of this Universe, the human brain is basically incapable of understanding quantum level events. There's something happening here, but what it is ain't exactly clear... and never will be. So sayeth the Copenhagen convention.
I don't expect anyone on Slashdot to accept this on face value. But I do have a citation: check this out. One of the more obvious implications is that if you do not have a sense of humor, then becoming a quantum mechanic is not a good career choice for you.
Will
but we are certain it has fleas!
Untrue, and in fact the WHOLE POINT OF THIS ARTICLE is actually to describe why the 'classic' interpretation of the Uncertainty Principle doesn't work, because it doesn't explain how you can perform certain types of measurements on a set of entangled quantum states. This would not be possible if the "changing the state" interpretation was correct. In fact what is being established here is a more exact and in some sense looser type of Uncertainty Principle. Much like Newtonian Mechanics at the limit are indistinguishable from GR, so Heisenberg's UP is at the limit virtually indistinguishable from this new version they ARE different. The whole cat thing is just an illustration of ways in which they are different. Schoedinger's Cat is a lot like in classical physics accelerating something to relativistic velocities, the old-fashioned UP breaks down, we CAN observe some properties of the cat without deciding if it is alive or dead. In the end though once we DO know that, there's no going back, you'll never observe the dead cat and then the alive cat. That is still forbidden (technically just fantastically unlikely).
"Malo periculosam, libertatem quam quietam servitutem." -- Jefferson
That misses the point too though.
The original point of the Schrodinger's cat thought experiment was to highlight an absurdity of quantum mechanics: that if we chained enough causality to a quantum state, the mathematics showed that we ended up with conclusions like a living organism being both alive and dead at the same time (and then as time goes on, both alive and hungry, and dead and decaying, at the same time).
The obvious problem of this becomes more apparent when you consider the proposition that the cat has agency, or could be a physicist instead. If the experiment is collapsed by observation, what is observation, given as if we also locked a physicist in the box with the cat he too would be alive and dead at the same time.
"50/50" is probability, you need more than one experiment to decide the ratios of the two different states. The problem is, once you have made, say 1000 experiments you have really just moved 1000 steps along a path; there are other paths you could have ended up on. So maybe you come to exactly 50/50 as the ratio, but somewhere out there in the multiverse there is a world where the 1000 experiments led to a 70/30 ratio instead. You just cannot observe it because you diverged at some point: You are not there, you are here.
Is that a British torch or an American torch? The cat's fate may yet be undecided!
Dark Reflection
And if you wait for, say, three weeks until you open the box, the cat will almost definitely be dead.
Dark Reflection
The inside of the box is a system, it is isolated from the outside of the box. It is irrelevant that parts of the system inside the box can measure other parts. Quantum superposition is a relative state, as far as the insides of the box are concerned there is no superposition, but to the observers OUTSIDE, until they exchange information with the inside, the superposition exists. Moreover these superpositions are NOT just artifacts of insufficient knowledge. Bell effectively proved this back in the 60's, though it seems to have taken a few decades for the full implications to dawn on the physics community.
Actually there is again no discussion of an "internal world". That would be a type of 'hidden variable' which is again excluded by Bell and this has been experimentally demonstrated, ther eare no hidden variables. Thus there is no "hidden [...] world that follows reasonable laws". It is indeed "weird all the way down" and we have experimentally verified this.
Of course the REAL thing you guys are all debating here is that it is (supposedly) impossible to create the degree of decoupling of the inside and outside of the box that would be necessary to remain the cat in the superposition for any finite length of time. Of course this is proving to be a rather shaky proposition, as we have now demonstrated superpositions of assemblies of billions of atoms. Albeit these things are much smaller than a cat, but they are nevertheless large enough to (barely) discern with the human eye. How unlikely is it that we will perfect techniques to create cat sized superpositions? I would bet heavily on it being feasible, if difficult.
"Malo periculosam, libertatem quam quietam servitutem." -- Jefferson
RightSaidFred chose his words carelessly. You are all correct but talking about different things.
Yes, there is "communication" in the sense of "spooky action at a distance". No, you cannot transmit classical information that way.
Except what we do know is that currently you're simply forbidden from transmitting information faster then light this way. There's nothing that would forbid "spooky action at a distance" from transmitting information at or below light speed, provided some means could be found to allow it to do that.
This would still be a huge discovery in a world where electromagnetic spectrum is highly limited and interceptible, and it's why I find these weak measurement experiments so interesting. You could imagine for example, that you have a big collection of spin-entangled electrons in a device, that you push around weakly, and then transmit a synchronization signal at light speed to indicate to a receiver that it's safe to read off the state of their entangled electrons. You wouldn't be able to talk faster then light, but you'd have wireless communications with effectively infinite bandwidth.
That was good, you should post from an account! ;)
"Malo periculosam, libertatem quam quietam servitutem." -- Jefferson
That was always the biggest piece of unnecessary technobabble. There's nothing "quantum" about the demands of the reassembling ordinary matter.
What bothered Einstein wasn't the superposition of dead and alive cats, it was the random nature of the collapse of the wave function in the first place. Einstein couldn't abide the existence of quantum statistics. He was opposed to the existence of the ENSEMBLE of cats. He would say that "God does not play dice" means that the universe is totally deterministic. He was in fact advocating for the existence of hidden variables which would restore causality to QM. Unfortunately for the good doctor Bell removed that possibility from the table decisively. There are no hidden variables, God does indeed figuratively 'roll the dice' and there is no way EVEN IN PRINCIPLE to know if the cat will live or die, even if you had the entire state of the quantum waveform of the whole universe and enough computing power to solve it for the cat's state, that state is still 50% dead and 50% alive, not one or the other.
"Malo periculosam, libertatem quam quietam servitutem." -- Jefferson
interpretation. In that interpretation there is no need to consider the question of 'observers'. Quantum states are relative, and to say that a waveform has 'collapsed' is just a statement about its relationship with certain other parts of the system. Thus it is irrelevant that the cat could 'observe itself', this is surely true, but then it is only alive or dead in relationship to itself (and the rest of the inside of the box). To observers outside the box it is in a superposition because that is how they are relating to the part of the system inside the box. Eventually probability dictates that information will leak out and the outside observers relationship to the state inside the box will evolve, they will see the waveform collapse and the cat will become definitely alive or dead to them as well. Note that again this is not just a way of saying that the people outside the box "don't know yet", there are ACTUAL experiments they can perform who's results differ between "don't know" and "waveform hasn't collapsed" (again, Bell Inequalities).
"Malo periculosam, libertatem quam quietam servitutem." -- Jefferson
Honestly, I have tried to understand the thought experiment but what I know of reality keeps getting in the way. Who cares if you KNOW whether the cat is alive or dead before you open the box? If the cat is alive, it does not matter. If the cat is dead, you can check the decomposition of the cat and know when it died. I just HAVE to be missing something here. How can the cat REALLY be both alive and dead when you can check on the exact time of death?
"Someone needs to talk to the tree of liberty about its ghoulish drinking problem." by ohnocitizen
Laplace is still correct, and Prof. Taleb, in his book, The Black Swan, cleverly destroyed this entire uncertainty stuff. At the quantum level, it averages out.
When I try to explain this thought experiment to non-techies (or laymen in general), I use the following:
Imagine a box where you throw in a coin. Close the box and rattle it around. Schrodinger's theory is that the coin is both face up and face down (as seen from the top of the box).
Is this an accurate analogy? Schrodinger's cat had too many pieces and explaining it tended to be too complicated.
We don't live in Shouldland.
Getting away from the whole "undead felines" thing, what are the implications for what was supposed to be the next big thing for secure communications, Quantum Encryption?
My understanding of quantum encryption was that what theoretically made it secure was that any attempt to read the data by a man in the middle would necessarily corrupt the data, making the tap obvious. But if the man in the middle is able to read the qbits without changing them, doesn't the whole concept of quantum encryption fail?
I've been saying for YEARS that the reason we even have this Quantum Uncertainty that some cat likes to pretend is a law of physics, is because the "probing" of quantum states is equivalent to "measuring car movements by launching bowling balls at them".
So "subtler measurements" means you don't disturb the "quantum state"? How obvious is this that it's taken us 20 years?
Quantum theory, while strong on the applied math, seems to be riddled with absolute nonsense as a logical model. They proposed particles being "aware".
I'll also make another prediction; that the very nature of "quantum" or better stated "we can't find an electron halfway between orbital shells" -- is that waves interact with other waves on their peaks, or when in opposite phase. So this entire paradigm of "particles for every force" would also exactly fit "everything is a wave function on some type of medium -- whether you call it Pixels or the Aether."
Anyway, that's my 2 cents on the matter -- but I'm only making sense of it based upon the theory -- not the math. So I'm not going after the "proofs" but the "visualization" of the concepts involved.
"Uncertainty" has always been a problem with measurement -- not with physics itself.
>>"ad space available -- low rates!!!"
Observation doesn't mean that an intelligent agent sees or gains knowledge of the state of the system. A photon is enough of an observer to determine the cat's state. The fact that you could do it with a physicist is mind-bending to consider, but has no importance to the question of what counts as observation.
A cat in a box is always bloody furious, that's what quantum physicists failed to account for.
First of all you probably HAVE measured a lot of it. QM is about 'interactions', not some sort of conscious observation. Secondly there's nothing at all odd or wrong with saying that "everything is in superposition with everything else". The ENTIRE UNIVERSE can be described by a single quantum wave form. There is ultimately in QM no such thing as "this thing" and "that thing". You can't even assert that any given electron or proton is a 'certain one' because they are all indistinguishable. Notionally there are many electrons in the universe, but you can as easily assume there is exactly one electron, so what exactly is it that is or isn't in 'superposition' with everything else, or not?
Truly, 99.99% of the way we think about the world is simply not fundamentally applicable to the quantum world. So what is or isn't sophistry when the very concepts of locality, causality, identity, and existence don't apply to the regime we're talking about? This why Feynman said "nobody understands quantum mechanics". He wasn't kidding.
"Malo periculosam, libertatem quam quietam servitutem." -- Jefferson
Except that said photon could also be part of the system. Or more importantly - the alive and dead physicist could do other things like unlock the box and get out of it, becoming a very much alive physicist who has just successfully collapsed their own quantum state.
Yes, but if that happens in a locked and windowless room, to observers outside of the room the entire room plus physicist is still in a super-position of alive and dead until they (or the physicist!) open the door to check. For someone outside the building the system of observers outside and the room are in a superposition until they check. See Wigner's friend.
The cat does know. The superposition is of a live cat (that knows it is alive) with a dead cat (that presumably doesn't know anything).
yes but cats do have 9 lives.
Star Trek transporters are just 3d printers.
thnx anon and others...
I agree you cannot transmit classical 'information' that way...also agree getting close is worth investigating
I theorize that yes, it is possible to have true 'quantum communication'...I conjecture that what we know of as 'wormholes' may or may not exist, but I do know that, **if** some kind of 'action at a distance' of two quantum entangled systems can communicate in 1/1 instantaneous Bergsonian time...that thing would probably be like what we classically think of as a 'wormhole' between the two quantum systems...
so basically, my theory would predict a 'quantum communication wormhole' which would behave similar to the theorized space/time wormhole ;)
Thank you Dave Raggett
No. An interaction with the photon just entangled it with the system. It's described fully with the Schrodinger equation.
If the authors are actually measuring a quantum state, i.e. not simply a probability, then this implies the cat really Is alive and dead. It's almost a proof of many worlds...