Kevin, Sheila, Daniel, Vicky

Here is the squeezing dB data from this time, which shows the quantum noise reduction with squeezing, relative to a model of quantum noise without squeezing. To sanity check IFO parameters, here is the no-sqz quantum noise model (dashed purple) is plotted alongside the full budget (solid red), plotting CTN (the -. and -- green lines), and the technical non-quantum noise estimate (grey), using the no-sqz times taken in this dataset. IFO & SQZ parameters used for modelling are shown in the title.

Note: this squeezing subtraction (estimated quantum noise w/sqz - quantum noise model w/o sqz) is model-dependent. We are still working to use a cross-correlation estimate of the technical noise, so we can calculate the quantum noise without squeezing w/o relying on a shot noise model (b/c the model depends on optical gain / ifo readout losses). In this analysis, the method this is reversed: we use the quantum noise model to get an estimate of technical noise, then subtract that technical noise estimate from squeezed darm, to see the quantum noise reduction with squeezing. Specifically, in PSD here we do the following:

     - tech noise = (meas darm no sqz) - (qn model no sqz)    --> this is better to get it from the dcpds correlated noise (but correlated noise includes QRPN, need to account for that accurately)
     - quantum noise w/sqz = (meas darm w/sqz - tech noise)
     - sqz dB = 10*log10( (quantum noise w/sqz) / (gwinc qn model no sqz) )

How I set the IFO modeling parameters:

1) Homodyne / readout angle = - 10.7 degrees. This is constrainted to < -10.7deg from sheila's recent contrast defect measurement 71913.
2) SRCL detuning =0.  It is likely small, though possibly non-zero; anyways, setting it to 0 for this analysis, while working with Louis to see the SRCL detuning from calibration measurements.
3) IFO readout efficiency - based on sqz wiki, expect ~13% broadband optical readout losses of the IFO signal, without squeezing. Based on no-sqz measured DARM, circulating arm powers in the 370-380kW range, homodyne angle < -10.7 deg, and negligible SRCL detuning -- here it is estimating 73% output efficiency (27% loss) to reconcile shot noise sensitivity with measured DARM at 1 kHz. With the no-sqz quantum noise model and 73% output efficiency, the estimated technical noise level is ~0.9e-20 m/rtHz at 1 kHz. This 1kHz technical noise estimate lands somewhere between Craig's correlated noise estimate 71333 (like 0.5-1e-20 m/rtHz @ 1kHz), Sheila's measurement of correlated dcpd noise 70891 (like 1.2e-20 m/rtHz @ 1kHz), recent noise budget projections, 72245, and a lil higher than Jenne's NonSENS noise budget 72578 (considering laser frequency noise ~0.3e-20m/rtHz at 1kHz). Given that subtracting the shot noise model suggests technical noise within a factor of 2-3 of other metrics, it lends at least some some confidence to the no-sqz quantum noise model w/excess output losses that impact optical gain.

Next question:  How well constrained is the breakdown between readout / injection losses? Not all the IFO readout losses that affect optical gain have to be SQZ readout losses (two beams could have different alignments/mode-matchings through the IFO / AS port). But to look for sqz losses, it'd be helpful to have a hint of where to look, if we can find whether losses are IFO side or else SQZ side. I don't see a clear sign in our measurements either way.
--> I considered 3 scenarios:
1) Equal IFO readout losses 20% + SQZ injection losses 20%,
2) Using same IFO readout losses (71%) for SQZ, then rest is SQZ injection losses (9%),
3) All SQZ injection losses (35%) and perfect readout efficiency (100%).
Noticeable features that could distinguish between the two scenarios (high readout losses vs. high injection losses) are mostly the low frequency QRPN SQZ rotation+gain from the arm cavities optomechanics. If more quantum noise is injected to the IFO (so injection losses * gen sqz dB are higher), then the arm cavities have more sqz to rotate, and so we see the squeezing efficiencies increase at low freqencies as a result. Kevin has nice plots that show this (squeezing efficiency within the arm cavity bandwidth decreases w/injection losses but not with readout losses; or like Kevin says, injection losses source QRPN and shot noise, while readout losses only source shot noise.

Some next steps to understand in the analysis/models:
1) How is the squeezing relatively flat given the known mode-mismatches of both IFO-OMC and SQZ-IFO/OMC? It seems that hot OM2 curvature leads to ~10% IFO-OMC mode mismatch, while the SQZ PSAMS are railed without yet optimizing SQZ-OMC mode-matching, so SQZ-OMC is clearly not perfectly mode-matched either. What is the scenario where we get flat squeezing given the known mode mismatch?
2) Use cross-correlation to calculate squeezing dBs. Is the squeezing definitely flat, or is that an artifact of how we compare to a quantum noise model?

Small notes about this analysis:
-- for 8/2 data: for calibration, I am using GDS-CALIB_STRAIN_CLEAN, with the text-file magnitude correction from Vlad's alog 71787.
-- for no-sqz noise budgeting, I am plotting both what gwinc has as CTN, and a trace that is 1.3e-20m/rtHz at 100 Hz. Reminder of this alog from Kevin K. and Evan H. regarding the CTN gwinc noise budget update 68499, which dropped the CTN estimate from ~1.3e-20 m/rtHz previously (green -. trace) to the ~1.13e-20 m/rtHz calculated in gwinc now (green, -- dashed line).