Sheila, Kiwamu, Evan, Stefan

Today we first recommissioned the QPD transmon to ITM loops.
- We set the transmon QPD offsets to zero at 10W input power and engaged all four loops. This brought the recycling gain up to about 40 consistently.
- The optimal QPD offset seems to slightly depend on input power, which is why we set them at 10W for now.
- We want to see whether this type of QPD loop is consistent from day to day before we physically center them.
- The loops are now engaged at low bandwidth in the script.
- We haven't designed propper plant inversion and roll-off filters for the loops..

Next we went to low noise and re-examined the SRCL coupling For some reason the SRCL coupling gave no subtraction at all - just some noise reshaping. (It could be due to our QPD-to-ITM loop.)
- We remeasured the coupling by i) first driving SRC_EXC, and measuring the TF from SRCL_OUT to DARM_IN1, and ii) SRCFF to DARM_IN1. iii) the ratio i/ii should be the desired FF path.
- We first hand-fitted the TF: 
    poles: 0,0, 800 (Q=2)     zeros: 32 (Q=7) , -180
    or
    zpk([2.28571+i*31.9183;2.28571-i*31.9183;-180],[0;0;200+i*774.597;200-i*774.597],1,"n")gain(5)

- Note the negative frequency zero - a clear indication that we have two coupling paths. We should just design two separate FF path - this would allow for easy individual tuning of low and high frequency feed-forward.

- Unfortunately an earthquake struck during the filter designing, so we couldn't test them.