Quantum Bayesian Networks

September 30, 2012

Weak Measurements Remind me of…

Filed under: Uncategorized — rrtucci @ 11:22 pm

I hate to say it but weak measurements remind me of homeopathy. It would be nice if someone did an experiment that measured the “same” quantity with a non-weak and a weak measurement, and compared the two results. Or are we to believe that weak measurements allow us to access parameters which non-weak measurements cannot access? But that would be a hidden variables theory, or something that went beyond standard quantum mechanics, wouldn’t it. I don’t have time to think about this any further because I’m working on something else and my time is limited, but I hope others will.

My previous post on Weak Values:

Dull Measurements (aka Weak Measurements)

1. There is no doubt that standard quantum mechanics can be used to describe a weak interaction followed by a standard POVM measurement. Call that a weak measurement if you wish. Me personally, I think that is a bad name for it. Maybe weak-disturbance or weak-interaction measurement would be better.

I’ve only studied the subject of weak measurements superficially so I’m only speculating, but my hypothesis is that $\langle A \rangle_W$ doesn’t exist, but $|\langle A \rangle_W|^2 g$ does, just like when $x(t)$ is Brownian motion, the mean value of $\frac{dx}{dt}$ doesn’t exist but the mean value of $\frac{(dx)^2}{dt}$ does. This is a well-known (among laser physicists specially) generalization of Ito calculus to quantum mechanics (as described in the book by Gardiner, for example)

Comment by rrtucci — October 5, 2012 @ 2:44 am

2. Look, somebody did exactly what you proposed.

Surprise, surprise, there is really nothing to see! Precious to see how the article marvels at this surprising fact.

Science, ever marching progress …

Comment by Henning — October 25, 2013 @ 4:54 pm

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