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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
Not my Work! - HEX
Horror & SciFi Erotic Nudes
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?
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.
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
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
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
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.
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.
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.
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.
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
That's mumbo jumbo and simply untrue. Both have a state, peeking at one just tells you what the other is it doesn't change any state.
Quantum "instant" communication is impossible and will therefore never happen.
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
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"
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.
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.
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.
We only managed a quick peek, but the cat is definitely dead. Or asleep. We think.
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...
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.
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
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
Is that a British torch or an American torch? The cat's fate may yet be undecided!
Dark Reflection
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
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.