M1L5g_CQ7.txt

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OK, next question is we have a beam splitter.
We have two photodiodes, i1 and i2.
And now we measure.
It's important for balanced homodyne detection.
We can now take the two currents, and we can add them
or we can subtract them.
So the question is, if we add the two
currents, what is now the variant in the two currents?
Remember each current had a variance of n over 2.
So now you are asked, when you sum the currents
of the two photodetectors, what happens to the two variances?