I Exploring Measurements in Quantum Field Theory: From Light Cones to Bell Tests

[DrChinese]

When a detector clicks, the photon number is reduced by 1, and a single photon is left.

Thanks for your straightforward answer. Not trying to debate that answer (which is good), or to be clever or anything. Just wondering about these follow-up questions, if you care to consider.

a) In Bell tests, there are usually polarizing beam splitters before the detector. Is it still a biphoton after the PBS and before the detectors?

[Moderator's note: question b) and the responses it generated have been spun off into a separate thread here.]

(Actually simply looking for your take on this, and nothing more.)

 

[A. Neumaier]

Thanks for your straightforward answer. Not trying to debate that answer (which is good), or to be clever or anything. Just wondering about these follow-up questions, if you care to consider.

a) In Bell tests, there are usually polarizing beam splitters before the detector. Is it still a biphoton after the PBS and before the detectors?

If the state of the biphoton has a nonzero component in the polarizing direction, yes. If it is orthogonal to the polarizing direction, the particle number reduces by 1.

 

[DrChinese]

If the state of the biphoton has a nonzero component in the polarizing direction, yes. If it is orthogonal to the polarizing direction, the particle number reduces by 1.

Thanks, answers my question nicely.

 

[Lord Jestocost]

A so-called measurement problem exists only for those who cling with ferocity to the assumption that the "state vector" is a representation of some reality behind the phenomena.

For those who don't cling to this assumption, a much more severe problem is that of connecting in an objective way the subjective probabilities associated with the vague psychological concept of knowledge to physical reality.

Unless they regard physics as a subdiscipline of psychology, they need to define precisely how and under which objective conditions this subjective knowledge changes.

The entire formalism of QM is a computational recipe for predicting the probabilities of various observable macroscopic outcomes. Unlike classical probability, however, the quantum probability is not the probability of where - let's say for example - an electron is. It is the objective probability of where you (or anyone else) will find it in a particular experimental context. What the heck has this to do with pychology?

 

[A. Neumaier]

The entire formalism of QM is a computational recipe for predicting the probabilities of various observable macroscopic outcomes. Unlike classical probability, however, the quantum probability is not the probability of where - let's say for example - an electron is. It is the objective probability of where you (or anyone else) will find it in a particular experimental context. What the heck has this to do with pychology?

Psychology enters because the wave function is updated when the knowledge of the observer changes. Knowlege is a psychological property of an observer, not a physically well-defined state of the latter.

 

[PeterDonis]

Moderator's note: A subthread about temporal entanglement has been moved to its own thread:

https://www.physicsforums.com/threads/measurements-in-qft.1059303/post-6990834

I have also added a moderator's note in post #51 of this thread to show where the split begins.

 

[PeterDonis]

@DrChinese I have moved your latest post to the new thread on temporal entanglement. See the link in post #56.

 

[DrChinese]

@DrChinese I have moved your latest post to the new thread on temporal entanglement. See the link in post #56.

Thanks!