Question about Noise Floor

Hello… I have a question that is not specially hardware related, but more so about amplifier measurement… Please forgive if the question is inappropriate.
The question is about “Noise Floor”… Is a pre-amp noise floor of -140db to -150db theoretically and practically attainable.? Would it be measurable with any of the QA-40x analyzers…?

Thank You in advance

Hi @Vinylitic. Try reading this post, I think it will be helpful.

Hello Claudio… Thank you for your response and the lead to the post… I will review, and hope I will have a better understanding…