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Science

Quantum Measurements Leave Schrödinger's Cat Alive 210

Posted by samzenpus
from the looking-in-the-box dept.
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.'"
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Quantum Measurements Leave Schrödinger's Cat Alive

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  • by Sun (104778) <shachar@shemesh.biz> on Thursday October 04, 2012 @12:36AM (#41545801) Homepage

    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

  • by Intropy (2009018) on Thursday October 04, 2012 @12:47AM (#41545843)

    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.

  • by Anonymous Coward on Thursday October 04, 2012 @01:37AM (#41546031)

    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.

  • by Intropy (2009018) on Thursday October 04, 2012 @01:58AM (#41546101)

    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.

  • by WaffleMonster (969671) on Thursday October 04, 2012 @02:55AM (#41546271)

    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.

  • by expatriot (903070) on Thursday October 04, 2012 @05:55AM (#41546881)

    1. Stop being a jerk

    2. Look up the work on collapse of interference in the double slit experiment.

    3. If you can determine conclusively what constitutes an observation of a quantum system, you will be in line for a big prize.

    4. Ignore any discussion of cats. It is a joke that everyone has fallen for.

  • by jsternbe (703721) on Thursday October 04, 2012 @06:54AM (#41547127)
    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.

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