I am an electrical engineering by trade, working on the analogue part (Transmitter & Receiver) of a quantum optical communication channel. By this, I mean I have not much experience on things quantum.
There are, however, some notions or concepts that I would like to understand, but no matter how much I read articles I don't seem to be able to get a clear answer.
My question would be:
- What does it mean for a hetero- or homodyne receiver to be operating in the Quantum Shot Noise limit?
There are some notions that I have (I don't know if my assumptions are wrong).
- Shot noise is caused by the uneven production/arrival of photons. When the rate of arrival is high enough, we can model this noise as following a Gaussian distribution. If the rate is low (related to the power of the laser, I wager in relation to the Local Oscillator (LO)), we have to model it as a Poisson distribution.
- Dark current of photodetectors can also be modelled as such.
- It is important to operate near the Shot Noise Limit. I don't know exactly why, but some potential hypothesis:
- It limits/allows the elimination of electrical noise in post-processing
- Uncorrelates LO power with signal power, facilitating detection of states
- Simply improves detection by reducing overall noise floor (the more power, the more shot noise)
At the end of the end, what I would like to know is:
- Is the shot noise limit in such a configuration absolute or relative? That is, does it depend on the power level of the LO, or is it a fixed value (beyond physical parameters of the system) that one approaches as the power level of the LO is reduced?
- What would be a formula for determining what the power level of the LO should be for the system to be operating at the Shot Noise Limit?
Apologies if this is too long.
