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Now We Can See If That Cat Is Alive Or Dead: Peeking Inside Schrodinger's Box


Alan McDougall
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http://www.science20.com/news_articles/now_we_can_see_if_cat_alive_or_dead_peeking_inside_schrodingers_box-128037

 

Now We Can See If That Cat Is Alive Or Dead: Peeking Inside Schrodinger's Box

 

Direct measurements consists of two types of measurements performed one after the other, first a "weak" measurement followed by a "strong" measurement. In quantum mechanics the act of measuring a quantum state disturbs it irreversibly, a phenomenon referred to as collapse of the wave-function. The trick lies with the first measurement being so gentle that it only slightly disturbs the system and does not cause the wave-function to collapse.

 

"It is sort of like peeking into the box to see if Schrodinger's cat is alive, without fully opening the box," said lead author Dr. Mehul Malik, currently a post-doctoral research fellow at the University of Vienna and who was a PhD.D. in Boyd's group when the work was performed. "The weak measurement is essentially a bad measurement, which leaves you mostly uncertain about whether the cat is alive or dead. It does, however, give partial information on the health of the cat, which when repeated many times can lead to near certain information as to whether the cat is alive or dead."

 

Very interesting?

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It's a terrible over-exaggeration. Weak measurement is very exciting but it is not what numerous press releases (and articles c-n-p'd from press releases) claim. The bit about the cat seems particularly weird; there is no state for the cat till the wave function collapses - it is not just hidden but is the superposition of two states. The blog and press release seems to be saying that it is a hidden variable which through multiple readings we can gain insight into which of the states it will collapse into - but we cannot know what will happen because it hasn't yet happened (if it had a single state we could get hints about then it would hardly be interesting). The whole point of a superposition is that the both states "exist" (for a certain definition of "exist") at the same time - therefore there is no final outcome to take a weak sneak peek at.

 

we have had a fair few threads on weak measurement - probably here or in QM. Have a look around - I will see if I can drag out some links.

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It's a terrible over-exaggeration. Weak measurement is very exciting but it is not what numerous press releases (and articles c-n-p'd from press releases) claim. The bit about the cat seems particularly weird; there is no state for the cat till the wave function collapses - it is not just hidden but is the superposition of two states. The blog and press release seems to be saying that it is a hidden variable which through multiple readings we can gain insight into which of the states it will collapse into - but we cannot know what will happen because it hasn't yet happened (if it had a single state we could get hints about then it would hardly be interesting). The whole point of a superposition is that the both states "exist" (for a certain definition of "exist") at the same time - therefore there is no final outcome to take a weak sneak peek at.

 

we have had a fair few threads on weak measurement - probably here or in QM. Have a look around - I will see if I can drag out some links.

 

Thanks!

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