The preliminary message from today's squeezing measurements on the homodyne is that it seems like we do not have any large extra losses or phase noise when we are measuring using the homodyne, using the PSL as a local oscillator. I will continue and do these measurements for a few different nonlinear gains during tomorrow's maintenance window.
Earlier today I went to HAM6 while Jenne and Georgia were working on increasing the input power to make some squeezing measurements on the squeezer. I mostly followed Haocun's procedure on the git wiki: Measurement procedure
Since I used the PSL LO, there was only about 0.75mW of total LO power available, so that is what I used. The table below shows visibility measurements taken in both the positive and negative homodyne arms, the first set was after my first attempt, I then realized that I had messed up the balancing of the homodyne, and went to a couple of meetings. After I came back, I got the second set of measurements. In both cases the asymmetry between the two arms I think indicates that the balancing isn't that good, but since the shot noise spectrum looked flat I went ahead with the measurements anyway.
I noticed that when I looked at the intensity noise on the LO, in either arm of the homodyne, there is a large whistling line. It also shows up in the squeezing spectrum, although much smaller.
| dark offset = -1.3e-3V | ||||
| max | -3.56 | 3.3 | 2.93 | -3.15 |
| min | -80e-3 | 66e-3 | 24e-3 | -40e-3 |
| vis | 96% | 96% | 98% | 98% |
For the nonlinear gain I measured 79.5 counts on the OPO IR diode without green, and locked the maximum amplification gave 139 counts, de-amplification gave 56.5 counts, so that is a nonlinear gain of 1.75 or x=0.244
The data is saved on a floppy disk, so plots can be produced. I read off the display 3.5dB of squeezing and 4.7dB of anti squeezing. With the total efficiency of 0.9 (escape efficiency= 0.98, VIP transmission= 0.96, visibility^2 = 0.96, quantum efficiency=0.99), and no phase noise, we would expect 3.6dB of squeezing and 4dB of anti squeezing, so this is actually a little bit too much anti squeezing.
For the homodyne visibility measurements, I used the guardian state LOCKED_SEED_HIGH, but made some changes to thresholds, and added those thresholds to the sqzparams file. I had trouble using the LO guardian for the homdyne, and since it is difficult to debug guardian code on the imacs, I just closed and opened the LO loop manually.